WO2019098330A1

WO2019098330A1 - Laser peening method, method for producing reformate, laser peening device, and metal material

Info

Publication number: WO2019098330A1
Application number: PCT/JP2018/042490
Authority: WO
Inventors: 陽一郎弘中; 啓介重森; 健之松岡; 宏併宮西; 典雅尾崎; 兒玉　了祐; 永祐三浦; 隆之助黒田
Original assignee: 国立大学法人大阪大学; 国立研究開発法人産業技術総合研究所
Priority date: 2017-11-17
Filing date: 2018-11-16
Publication date: 2019-05-23
Also published as: JPWO2019098330A1

Abstract

This laser peening method involves a step (S21) for generating pulsed light PLD, and a step (S23) for irradiating the surface (5a) of a target (5) with the pulsed light (PLD) so as to form an irradiation region (W2) surrounding a non-irradiation region (W1) on the surface (5a) of the target (5). The peak value (PV) of the compression residue stress applied to the target (5) on the basis of the pulsed light (PLD) is positioned deeper with respect to the non-irradiation region (W1) the greater the diameter (DM1) of the non-irradiation region (W1).

Description

Laser peening method, reformate production method, laser peening apparatus, and metal material

The present invention relates to a laser peening method, a modified product production method, a laser peening apparatus, and a metal material.

In the laser peening method described in Patent Document 1, a laser beam is irradiated from the pulse laser device to the surface of a workpiece through a reflecting mirror and a moving reflecting mirror. Specifically, the workpiece is placed in the transparent liquid, and the movable reflecting mirror irradiates the laser light while changing the irradiation position on the surface of the workpiece. As a result, compressive stress remains on the surface of the workpiece. That is, a residual stress field of compression (hereinafter, referred to as "compression residual stress field") is formed on the surface of the workpiece.

Unexamined-Japanese-Patent No. 7-246843

However, in the laser peening method described in Patent Document 1, only a relatively thin compressive residual stress field is formed in the workpiece.

The present invention has been made in view of the above problems, and an object thereof is to provide a laser peening method capable of forming a relatively thick compressive residual stress field, a modified product production method, a laser peening apparatus, and a metal material. It is to do.

According to one aspect of the present invention, a laser peening method includes the steps of: generating pulsed light; and applying the pulsed light to the surface of the object so as to form an irradiated area surrounding a non-irradiated area of the surface of the object. And irradiating.

In the laser peening method of the present invention, the peak value of the compressive residual stress applied to the object based on the pulse light is positioned deeper with respect to the non-irradiated area as the diameter of the non-irradiated area is larger. It is preferable to do.

In the laser peening method of the present invention, the step of generating the pulse light includes the step of adjusting the diameter of the non-irradiation area to control the position of the peak value of the compressive residual stress in the depth direction. Is preferred. It is preferable that the depth direction indicates a direction in which the depth is larger than the non-irradiated area.

In the laser peening method of the present invention, the radius of the non-irradiated area is substantially equal to the depth relative to the non-irradiated area of the peak value of the compressive residual stress applied to the object by the shock wave based on the pulsed light. Is preferred.

According to another aspect of the present invention, a laser peening method includes the steps of: generating a first pulse light and a second pulse light; and forming the first irradiation region on a surface of an object. And irradiating the surface of the object with the second pulse light so as to form a second irradiation region on the surface of the object. The second irradiation area surrounds the first irradiation area. The intensity of the first pulse light in the first irradiation area is different from the intensity of the second pulse light in the second irradiation area. The intensity of the first pulse light indicates the energy of the first pulse light per unit time and per unit area. The intensity of the second pulse light indicates the energy of the second pulse light per unit time and per unit area.

In the laser peening method of the present invention, it is preferable that the intensity of the first pulse light in the first irradiation area is smaller than the intensity of the second pulse light in the second irradiation area.

In the laser peening method of the present invention, it is preferable that the intensity of the first pulse light in the first irradiation area is larger than the intensity of the second pulse light in the second irradiation area.

In the laser peening method according to the present invention, the peak value of the compressive residual stress applied to the object based on the first pulse light and the second pulse light may be higher as the diameter of the first irradiation region is larger. It is preferable to be located at a deep position with respect to one irradiation area.

In the laser peening method according to the present invention, the step of generating the first pulse light and the second pulse light adjusts the diameter of the first irradiation region to measure the depth direction of the peak value of the compressive residual stress. Preferably, the step of controlling the position of The depth direction preferably indicates a direction in which the depth is larger than the first irradiation area.

According to still another aspect of the present invention, in the method of producing a reformate, the target is reformed by the above-described laser peening method to produce a reformate.

According to still another aspect of the present invention, a laser peening apparatus includes a pulse generation unit and a pulse irradiation unit. The pulse generation unit generates pulsed light. The pulse irradiation unit irradiates the surface of the object with the pulse light so as to form an irradiation area surrounding the non-irradiation area of the surface of the object.

According to still another aspect of the present invention, a laser peening apparatus includes a pulse generation unit and a pulse irradiation unit. The pulse generation unit generates a first pulse light and a second pulse light. The pulse irradiation unit irradiates the surface of the object with the first pulse light so as to form a first irradiation area on the surface of the object, and forms a second irradiation area on the surface of the object. The second pulsed light is irradiated to the surface of the object. The second irradiation area surrounds the first irradiation area. The intensity of the first pulse light in the first irradiation area is different from the intensity of the second pulse light in the second irradiation area. The intensity of the first pulse light indicates the energy of the first pulse light per unit time and per unit area. The intensity of the second pulse light indicates the energy of the second pulse light per unit time and per unit area.

According to yet another aspect of the invention, a metallic material comprises a body having a surface and a portion. The portion is located at a position distant from the surface in the depth direction. In said part, the compressive residual stress has a peak value. The compressive residual stress is attenuated from the portion toward the depth direction while being repeatedly reduced and increased.

In the metal material of the present invention, it is preferable that the surface has an irradiation area of pulse light and a non-irradiation area of the pulse light. The non-irradiation area is preferably surrounded by the irradiation area. Preferably, the depth of the portion with respect to the non-irradiated area is substantially equal to the radius of the non-irradiated area.

According to the invention it is possible to create relatively thick compressive residual stress fields.

BRIEF DESCRIPTION OF THE DRAWINGS (a) is a figure which shows the laser peening apparatus which concerns on Embodiment 1 of this invention. (B) is a flowchart which shows the laser peening method performed by the laser peening apparatus which concerns on Embodiment 1. FIG. (C) is a figure which shows the 1st irradiation area | region and 2nd irradiation area | region by the laser peening apparatus which concern on Embodiment 1. FIG. (A) is a schematic diagram which shows the 1st shock wave and 2nd shock wave by the laser peening apparatus which concern on Embodiment 1. FIG. (B) is a schematic diagram which shows the wave face of the 1st shock wave by the laser peening apparatus which concerns on Embodiment 1, and a 2nd shock wave. (A) is a figure which shows the 1st pulsed light by the laser peening apparatus which concerns on Embodiment 1. FIG. (B) is a schematic diagram which shows the 1st shock wave by the laser peening apparatus which concerns on Embodiment 1, and the shock wave which concerns on a comparative example. (A) is a graph which shows the residual-stress field formed in the target object by the laser peening apparatus concerning Embodiment 1. FIG. (B) is typical sectional drawing which shows the target object modify | reformed by the laser peening apparatus which concerns on Embodiment 1. FIG. (A) And (b) is a figure which shows an example of the formation principle of the compressive residual stress field by the laser peening apparatus which concerns on Embodiment 1. FIG. It is a figure which shows the laser peening apparatus which concerns on Embodiment 2 of this invention. FIG. 7 is a schematic cross-sectional view showing an optical unit of a laser peening apparatus according to a second embodiment. It is a graph which shows the relationship between the ablation pressure by the laser peening apparatus which concerns on Embodiment 2, and the intensity | strength of 1st pulse light and 2nd pulse light. (A) is a figure which shows the laser peening apparatus which concerns on Embodiment 3 of this invention. (B) is a flowchart which shows the laser peening method performed by the laser peening apparatus which concerns on Embodiment 3. FIG. (C) is a figure which shows the non-irradiation area | region and irradiation area | region by the laser peening apparatus which concern on Embodiment 3. FIG. (A) is a graph which shows the residual-stress field formed in the target object by the laser peening apparatus which concerns on Embodiment 3. FIG. (B) is typical sectional drawing which shows the target object modify | reformed by the laser peening apparatus which concerns on Embodiment 3. FIG. (A) And (b) is a figure which shows the formation principle of the compressive residual stress field by the laser peening apparatus which concerns on Embodiment 3. FIG. FIG. 8 is a view showing details of a laser peening apparatus according to a third embodiment. It is a figure which shows the residual stress field which concerns on 1st Example of this invention. (A) is a figure which shows the 1st irradiation area | region and 2nd irradiation area | region which concern on 1st Example. (B) is a figure which expands and shows a part of 1st irradiation area | region which concerns on 1st Example. (C) is a figure which expands and shows a part of 2nd irradiation area | region which concerns on 1st Example. (A) is a figure showing the depth of the 1st irradiation field concerning the 1st example, and the 2nd irradiation field. (B) is a perspective view which shows the 1st irradiation area | region and 2nd irradiation area | region which concern on 1st Example. (A) is a figure which shows the 1st pulsed light which concerns on 1st Example. (B) is a figure which shows the 2nd pulsed light which concerns on 1st Example. It is a graph which shows the relationship of the particle velocity and time which concern on 1st Example. (A)-(d) is a figure which shows the shock wave which concerns on 2nd Example of this invention in a time series. FIGS. 18 (a) to 18 (d) are shockwaves according to the second embodiment, showing shockwaves after the shockwaves shown in FIG. 18 (d) in time series. It is a figure which shows the residual stress field which concerns on 3rd Example of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference characters and description thereof will not be repeated. Further, in order to simplify the drawing, hatching indicating a cross section is appropriately omitted.

(Embodiment 1)
A laser peening apparatus 100 according to a first embodiment of the present invention will be described with reference to FIGS. 1 (a) to 3 (b). First, the configuration and operation of the laser peening apparatus 100 will be described with reference to FIGS. 1 (a) to 1 (c).

FIG. 1A shows a laser peening apparatus 100. FIG. FIG. 1 (b) is a flowchart showing a laser peening method performed by the laser peening apparatus 100. FIG.1 (c) is a figure which shows 1st irradiation area | region A1 and 2nd irradiation area | region A2 by the laser peening apparatus 100. As shown in FIG.

As shown to Fig.1 (a), the laser peening apparatus 100 performs laser peening with respect to the target object 5. As shown in FIG. The laser peening is a technique of forming a residual stress field of compression (hereinafter referred to as “compression residual stress field”) inside the object 5 by irradiating the surface of the object 5 with pulsed laser light. It is. Specifically, when the surface of the object 5 is irradiated with pulse laser light, the surface of the object 5 is ablated and plasma is generated on the surface of the object 5. Furthermore, due to the action of plasma, that is, the ablation pressure by the plasma, a shock wave is generated and the shock wave propagates inside the object 5. Then, a compressive residual stress field is formed inside the object 5 by the shock wave. As a result, the strength of the object 5 increases and the object 5 becomes tough.

In the first embodiment, the object 5 is a target TA that forms a compressive residual stress field. The object 5 is, for example, a metal. The material of the object 5 is not particularly limited. In the first embodiment, the object 5 is placed in air or in a vacuum.

The laser peening apparatus 100 includes a pulse generation unit 1 and a pulse irradiation unit 3. And as shown in FIG.1 (b), the laser peening apparatus 100 performs the laser peening method. The laser peening method includes steps S1 and S3.

In step S1, the pulse generation unit 1 generates a first pulse light PL1 and a second pulse light PL2. Each of the first pulse light PL1 and the second pulse light PL2 is a laser light.

Next, as shown in FIG. 1 (b) and FIG. 1 (c), in step S3, the pulse irradiation unit 3 forms the first pulse so that the first irradiation area A1 is formed on the surface 5a of the object 5. The surface 5 a of the object 5 is irradiated with the second pulse light PL 2 so that the surface 5 a of the object 5 is irradiated with the light PL 1 and the second irradiation area A 2 is formed on the surface 5 a of the object 5. In the first embodiment, the surface 5 a of the object 5 is irradiated with the single first pulsed light PL 1 and the single second pulsed light PL 2.

The first irradiation area A1 has a substantially circular shape. Specifically, the first pulse light PL 1 forms a substantially circular irradiation region on the surface 5 a of the object 5. The substantially circular irradiation area by the first pulse light PL1 is a first irradiation area A1.

The second irradiation area A2 surrounds the first irradiation area A1. The second irradiation area A2 has a substantially annular shape surrounding the first irradiation area A1. Specifically, the second pulse light PL 2 forms a substantially circular irradiation region on the surface 5 a of the object 5. Among the substantially circular shaped irradiation areas by the second pulse light PL2, the “generally annular area” excluding the “central substantially circular area” is the second irradiation area A2. The “central substantially circular area” overlaps the first irradiation area A1. The diameter DM2 of the second irradiation area A2 is larger than the diameter DM1 of the first irradiation area A1. The diameter DM1 of the first irradiation area A1 corresponds to an example of the “diameter of the first irradiation area”.

The intensity of the first pulse light PL1 in the first irradiation area A1 is different from the intensity of the second pulse light PL2 in the second irradiation area A2. Hereinafter, the intensity of the first pulse light PL1 in the first irradiation area A1 will be referred to as “intensity K1”, and the intensity of the second pulse light PL2 in the second irradiation area A2 will be referred to as “intensity K2”. In the substantially circular irradiation area by the second pulse light PL2, “the substantially circular area at the center” overlaps the first irradiation area A1, so the first pulse PL1 and the second pulse PL2 cause the first irradiation. The intensity in the irradiation area A1 is “K1 + K2”.

The intensity K1 of the first pulse light PL1 indicates the energy of the first pulse light PL1 per unit time and per unit area. Specifically, the intensity K1 of the first pulse light PL1 is calculated by the following equation.
K1 = E1 / (PT1 × AR1)

“E1” indicates the energy of the first pulse light PL1 (for example, the unit is Joule: J). “PT1” indicates the time width (for example, the unit is seconds: s) of the first pulse light PL1. "AR1" shows the area (for example, a unit is square centimeter: cm < ² >) of 1st irradiation area | region A1. “E1 / PT1” indicates the power (for example, unit: watt: W).

The intensity K2 of the second pulse light PL2 indicates the energy of the second pulse light PL2 per unit time and per unit area. Specifically, the intensity K2 of the second pulse light PL2 is calculated by the following equation.
K2 = E2 / (PT2 × AR2)

“E2” indicates the energy (for example, J) of the second pulse light PL2. “PT2” indicates the time width (for example, s) of the second pulse light PL2. “AR2” indicates the sum (for example, cm ² ) of the area of the first irradiation area A1 and the area of the second irradiation area A2. That is, “AR2” indicates the area of the irradiation region of the second pulse light PL2. “E2 / PT2” indicates the power (eg, W).

Each of the time width PT1 and the time width PT2 is, for example, several femtoseconds to several hundreds nanoseconds.

As described above with reference to FIGS. 1A to 1C, the first pulse light PL1 is applied to the first irradiation area A1. Accordingly, a shock wave (hereinafter, referred to as “first shock wave SW1”) traveling from the first irradiation area A1 to the inside of the object 5 is generated. In addition, the second pulse light PL2 is applied to the second irradiation area A2. Accordingly, a shock wave (hereinafter, referred to as “second shock wave SW2”) directed from the second irradiation area A2 to the inside of the object 5 is generated.

Then, since the intensity K1 of the first pulse light PL1 and the intensity K2 of the second pulse light PL2 are different, the velocity of the first shock wave SW1 is different from the velocity of the second shock wave SW2. Therefore, the case where the second shock wave SW2 is not generated due to the interaction between the first shock wave SW1 and the second shock wave SW2 or the interaction between the pressure waves facing each other across the first shock wave SW1 in the second shock wave SW2 In comparison, the shock wave propagates to the deep position of the object 5 below the first irradiation area A1. As a result, a compressive residual stress field can be formed to a relatively deep position of the object 5. In other words, it is possible to form a relatively thick compressive residual stress field inside the object 5. “Depth” indicates the depth of the object 5 with respect to the surface 5 a.

In other words, in the first embodiment, the object 5 is modified by forming a compressive residual stress field in the object 5 by the laser peening method described with reference to FIG. Therefore, in the first embodiment, the object 5 is reformed by the laser peening method described with reference to FIG. 1 (b) to produce a modified product (hereinafter referred to as “reformed product 51”). A method of producing a material is provided. In addition, the reformed product 51 in the case where the object 5 is a metal may be described as “metal material 51A”.

When the compressive residual stress field can be formed to a relatively deep position of the object 5, the fatigue strength of the object 5 (for example, metal) can be improved, and the occurrence of stress corrosion cracking in the object 5 can be suppressed. As a result, the durability of the object 5 can be improved. For example, the present invention is effective in forming a compressive residual stress field in materials (object 5) used in industries requiring high safety (for example, the aircraft industry and the nuclear industry).

Further, according to the first embodiment, by using the second shock wave SW2 in addition to the first shock wave SW1, the object 5 is compared without forming the target in which the specific layer LY is disposed on the surface of the target TA. The compressive residual stress field is formed to the deepest position. Therefore, the operation of arranging the specific layer LY on the surface of the target TA can be omitted. As a result, the cost at the time of forming a compressive residual stress field can be suppressed. The specific layer LY is a layer that assists in forming a compressive residual stress field in the target TA. The specific layer LY will be described later.

Furthermore, in the first embodiment, it is preferable that the wavelength λ1 of the first pulse light PL1 be different from the wavelength λ2 of the second pulse light PL2. This is because the intensity K1 of the first pulse light PL1 and the intensity K2 of the second pulse light PL2 can be easily made different by making the wavelengths different.

In the first embodiment, the ablation pressure P generated on the surface 5 a of the object 5 is expressed by the following equation.
P = 0.86 × (K / λ) ^2/3

The unit of "P" is "terapascal: TPa". “K” indicates energy per unit time and unit area of pulsed light on the surface 5 a of the object 5, and the unit of “K” is “10 ¹⁴ W / cm ² ”. “Λ” indicates the wavelength of pulsed light, and the unit of “λ” is “μm”.

Therefore, the ablation pressure P1 based on the first pulse light PL1 is expressed as 0.86 × (K1 / λ1) ^2/3, and the ablation pressure P2 based on the second pulse light PL2 is 0.86 × (K2 / λ2). It is expressed as ^2/3 .

Therefore, by making the wavelength λ1 of the first pulse light PL1 different from the wavelength λ2 of the second pulse light PL2, the ablation pressure P1 and the ablation pressure P2 can be easily made different. As a result, it is possible to easily generate the first shock wave SW1 and the second shock wave SW2 having different speeds.

Furthermore, according to the first embodiment, the object 5 is irradiated with the first pulse light PL1 and the second pulse light PL2 to form a compressive residual stress field. As compared with the shot peening which is caused to collide with the surface 5a of the above, "large number of particles" to be discarded does not occur. Therefore, the pollution of the global environment by "a large number of particles" can be prevented. Moreover, compared with shot peening, a local compressive residual stress field can be easily formed on the object 5, and the operability of the apparatus can also be improved.

In the following description of Embodiment 1, unless otherwise specified, the intensity K1 of the first pulse light PL1 in the first irradiation area A1 is larger than the intensity K2 of the second pulse light PL2 in the second irradiation area A2. . Therefore, the ablation pressure P1 generated in the first irradiation area A1 is larger than the ablation pressure P2 generated in the second irradiation area A2. As a result, the peak pressure of the first shock wave SW1 becomes larger than the peak pressure of the second shock wave SW2, and the velocity of the first shock wave SW1 is faster than the velocity of the second shock wave SW2.

Next, the first shock wave SW1 and the second shock wave SW2 will be described with reference to FIGS. 2 (a) and 2 (b). FIG. 2A is a schematic view showing the first shock wave SW1 and the second shock wave SW2. In FIG. 2A, the vertical axis indicates pressure, and the horizontal axis indicates the position from the surface 5 a of the object 5. FIG. 2B is a schematic view showing wavefronts of the first shock wave SW1 and the second shock wave SW2. 2A and 2B show the first shock wave SW1 and the second shock wave SW2 inside the object 5 at a certain point in time.

As shown in FIGS. 2A and 2B, the first shock wave SW1 and the second shock wave SW2 propagate in the propagation direction D. The propagation direction D is substantially orthogonal to the surface 5 a of the object 5 and indicates the direction from the surface 5 a of the object 5 toward the inside of the object 5.

The peak value of the pressure of the first shock wave SW1 is larger than the peak value of the pressure of the second shock wave SW2. This is because the intensity K1 of the first pulse light PL1 in the first irradiation area A1 is larger than the intensity K2 of the second pulse light PL2 in the second irradiation area A2. Then, the velocity of the first shock wave SW1 is faster than the velocity of the second shock wave SW2.

As a result, according to the first embodiment, the interference between the first shock wave SW1 and the second shock wave SW2 suppresses the attenuation of the first shock wave SW1 due to the rarefaction wave (Rarefaction). In addition, the second shock wave SW2 suppresses the penetration of the lean wave from the side of the first shock wave SW1. Therefore, the first shock wave SW1 propagates to a deep position of the object 5, as compared to the case where the second shock wave SW2 is not generated. As a result, a compressive residual stress field can be formed to a relatively deep position of the object 5.

In general, a lean wave is generated in response to the end of irradiation of pulsed light. And the speed of the rarefied wave is faster than the speed of the shockwave. Thus, the lean wave catches up with the shockwave and attenuates it. However, in the first embodiment, since the second shock wave SW2 suppresses the attenuation of the first shock wave SW1 due to the lean wave, the compressive residual stress field can be formed to a relatively deep position of the object 5.

Further, according to the first embodiment, the first shock wave SW1 is propagated to the deep position of the object 5 by the interference between the first shock wave SW1 and the second shock wave SW2. Therefore, even when the object 5 does not have the specific layer LY, it is possible to form a relatively thick compressive residual stress field inside the object 5.

Furthermore, in Embodiment 1, it is also possible to form a compressive residual stress field to a depth on the order of millimeters (mm). For example, generally, depending on the product incorporating the object 5, the abrasion and / or mechanical impact of the object 5 may cause the compressive residual stress field to a depth of about several hundreds of μm of the object 5. As a result, the reliability and durability of the object 5 may not be sufficient. However, in the first embodiment, the reliability and durability of the object 5 can be further improved by forming the compressive residual stress field to a depth on the order of millimeters.

Next, with reference to FIGS. 3A and 3B, the first shock wave SW1 will be described in relation to the first pulsed light PL1. FIG. 3A shows the first pulse light PL1. In FIG. 3A, the vertical axis represents the intensity (arbitrary unit) of the first pulse light PL1, and the horizontal axis represents time (nanosecond: ns). FIG. 3B is a schematic view showing the first shock wave SW1 and the shock wave SWa according to the comparative example. In FIG. 3 (b), the vertical axis represents pressure, and the horizontal axis represents the position from the surface 5 a of the object 5. FIG. 3B shows the first shock wave SW1 and the shock wave SWa at a certain point in time.

As shown in FIG. 3A, preferably, the first pulse light PL1 is a tailored pulse, and the shape on the time axis of the first pulse light PL1 is asymmetric with respect to the peak of the first pulse light PL1. . Specifically, the first pulse light PL1 has a first slope SL1 and a second slope SL2 which are inclined in different directions. On the time axis, the first slope SL1 is located forward of the second slope SL2. The first slope SL1 is a gentler slope than the second slope SL2.

As a result, as shown in FIG. 3B, the slope of the edge EG1 of the first shock wave SW1 generated by the first pulse light PL1 is gentle compared to the slope of the edge EGa of the shock wave SWa according to the comparative example. is there.

The reason why the inclination of the edge EG1 of the first shock wave SW1 is gentle is that the first pulse light PL1 has a gentle first slope SL1. The reason why the slope of the edge EGa of the shock wave SWa is steep is because the shock wave SWa is generated by symmetrical pulse light having a Gaussian distribution (hereinafter referred to as “comparison pulse light PLC”).

Since the slope of the edge EG1 of the first shock wave SW1 is gentle, compared with the case where the sharp shock wave SWa of the edge EGa propagates, shear stress is effectively transmitted inside the object 5 by the propagation of the first shock wave SW1. It can be induced. In addition, the interaction between the first shock wave SW1 and the second shock wave SW2 different in speed from each other can more effectively induce a shear stress in the object 5. By effectively inducing shear stress, dislocations can be generated inside the object 5 with a relatively high dislocation density. In addition, the higher the dislocation density, the easier it is to retain the residual stress. As a result, according to the first embodiment, a compressive residual stress field can be effectively formed inside the object 5.

The gentle slope of the edge EG1 of the first shock wave SW1 indicates, in other words, that the strain speed due to the first shock wave SW1 is slow compared to the strain speed due to the shock wave SWa. The strain rate indicates the amount of change in strain per unit time inside the object 5. By slowing the strain rate, ie by relaxing the pressure gradient, the formation and growth of dislocations are promoted. As a result, according to the first embodiment, a compressive residual stress field can be effectively formed inside the object 5. For example, the strain rate by the first shock wave SW1 is three to four orders of magnitude smaller than the strain rate by the shock wave SWa.

Further, according to the first embodiment, since the shape on the time axis of the first pulse light PL1 is asymmetrical, the temperature rise of the object 5 is increased as compared with the case where the comparison pulse light PLC is irradiated to the object 5. It can be suppressed. Therefore, the dislocations can be suppressed from being annealed. As a result, the compressive residual stress field can be effectively maintained inside the object 5.

The second pulse light PL2 is preferably a tailored pulse, and the shape of the second pulse light PL2 is preferably similar to the shape of the first pulse light PL1. That is, the time width of the second pulse light PL2 is substantially the same as the time width of the first pulse light PL1. Further, similarly to the first pulse light PL1, the shape on the time axis of the second pulse light PL2 is asymmetric with respect to the peak of the second pulse light PL2.

Specifically, the second pulse light PL2 has a first slope SL12 and a second slope SL22 which are inclined in different directions. On the time axis, the first slope SL12 is located forward of the second slope SL22. And 1st slope SL12 is a gentle slope rather than 2nd slope SL22. Therefore, the inclination of the edge of the second shock wave SW2 generated by the second pulse light PL2 is gentle as compared to the inclination of the edge EGa of the shock wave SWa according to the comparative example. Since the slope of the edge of the second shock wave SW2 is gentle, a compressive residual stress field can be effectively formed inside the object 5, as in the case of the first shock wave SW1.

Further, since the shape on the time axis of the second pulse light PL2 is asymmetric, it is possible to suppress the temperature rise of the object 5 as in the first pulse light PL1. As a result, the compressive residual stress field can be effectively maintained inside the object 5.

The shape on the time axis of the comparison pulse light PLC is substantially symmetrical with respect to the peak of the comparison pulse light PLC. Further, the time width of the comparison pulse light PLC is, for example, substantially the same as the time width of the first pulse light PL1. In addition, the comparison pulse light PLC has a first slope and a second slope which are inclined in different directions. The first slope is located forward of the second slope on the time axis. The first slope of the comparison pulse light PLC is steeper than each of the first slope SL1 of the first pulse light PL1 and the first slope of the second pulse light PL2.

The time width of the pulsed light (the first pulsed light PL1, the second pulsed light PL2, and the comparative pulsed light PLC) is defined by the open time of the window for passing the pulsed light. For example, the time width of each of the first pulse light PL1, the second pulse light PL2, and the comparison pulse light PLC is 10 ns. The time width of the pulsed light may be defined by the full width at half maximum of the pulsed light, or may be defined by the width of the pulsed light when the intensity of the pulsed light is 1 / e ² of the maximum intensity.

Next, the object 5 in which the compressive residual stress field is formed will be described with reference to FIGS. 4 (a) and 4 (b). FIG. 4A is a graph showing the residual stress field formed on the object 5 by the laser peening apparatus 100. In FIG. 4A, the vertical axis indicates residual stress (megapascals: MPa), and the horizontal axis indicates depths (micrometers: μm) from the surface 5 a of the object 5. FIG. 4 (b) is a schematic cross-sectional view showing the object 5 modified by the laser peening apparatus 100.

As shown to Fig.4 (a), residual stress CT generate | occur | produces in the inside of the target object 5 to which 1st pulse light PL1 and 2nd pulse light PL2 were irradiated. FIG. 4A shows the residual stress CT below the center C of the first irradiation area A1. Positive values of residual stress CT indicate tensile residual stresses CTA, and negative values of residual stress CT indicate compressive residual stresses CTB.

Hereinafter, in the present specification, the tensile residual stress CTA may be described as “tensile residual stress CTA”, and the compressive residual stress CTB may be described as “compression residual stress CTB”.

Further, as shown in FIG. 4B, the object 5 (specifically, the reformed product 51 or the metal material 51A) includes a main body 53. The main body 53 has a surface 53a and a portion 53b. The surface 53a corresponds to the surface 5a. The surface 53a has a first irradiation area A1 and a second irradiation area A2. The portion 53 b is located at a position distant from the surface 53 a in the depth direction DP. Specifically, the portion 53b is located at a position substantially perpendicular to the depth direction DP with respect to the center C of the first irradiation area A1. That is, the portion 53b is located at the depth DTP with respect to the center C of the first irradiation area A1.

In the first embodiment, the depth direction DP is substantially perpendicular to the surface 53a and indicates a direction away from the surface 53a. Specifically, the depth direction DP indicates the direction in which the depth becomes larger than the first irradiation area A1. In the present specification, the lower side of the first irradiation area A1 indicates the depth direction DP side with respect to the first irradiation area A1, and the lower side of the center C of the first irradiation area A1 is the first irradiation area A1. The depth direction DP side with respect to the center C is shown.

As shown in FIGS. 4A and 4B, in the portion 53b, the compressive residual stress CTB has a peak value PV. The peak value PV indicates the maximum value of the absolute value of the compressive residual stress CTB. The compressive residual stress CTB is attenuated while repeatedly decreasing and increasing from the peak value PV in the depth direction DP. That is, the compressive residual stress CTB is attenuated while being repeatedly decreased and increased from the portion 53 b in the depth direction DP. Therefore, according to the first embodiment, compared with the case where the compressive residual stress monotonously decreases, the compressive residual stress CTB can be generated over a deep range in the depth direction DP. That is, it is possible to form a relatively thick compressive residual stress field. The reason that the compressive residual stress CTB is attenuated while being repeatedly decreased and increased is that the compressive residual stress CTB is generated due to the interference between the first shock wave SW1 and the second shock wave SW2.

Here, in the present specification and claims, “damping” of compressive residual stress indicates that the absolute value of compressive residual stress decreases, and “increase” of compressive residual stress indicates the absolute value of compressive residual stress. Indicates that the

Next, the relationship between the diameter DM1 of the first irradiation area A1 and the peak value PV of the compressive residual stress CTB will be described with reference to FIGS. 4 (a) and 4 (b). The peak value PV of the compressive residual stress CTB applied to the object 5 based on the first pulse light PL1 and the second pulse light PL2 is greater than the diameter DM1 of the first irradiation area A1 with respect to the first irradiation area A1. Located in a deep position. Therefore, according to the first embodiment, it is possible to control the position in the depth direction DP of the peak value PV of the compressive residual stress CTB by adjusting the diameter DM1 of the first irradiation area A1. The position in the depth direction DP of the peak value PV indicates the depth DTP.

Specifically, as shown in FIG. 1 (a) and FIG. 1 (b), the step S1 includes a step S11. Then, in step S11, the pulse generation unit 1 adjusts the diameter DM1 of the first irradiation area A1 to control the position in the depth direction DP (depth DTP) of the peak value PV of the compressive residual stress CTB. Specifically, by adjusting the optical system of the pulse generation unit 1, the diameter DM1 of the first irradiation area A1 is set. Accordingly, in step S3, the pulse irradiation unit 3 irradiates the surface 5a of the object 5 with the first pulse light PL1 so as to form the first irradiation area A1 having the diameter DM1 set in step S21. According to the first embodiment, as the laser peening method includes the step S11, the position in the depth direction DP of the peak value PV of the compressive residual stress CTB can be controlled.

As described above, in FIGS. 2A to 4B, the case where the intensity K1 of the first pulse light PL1 in the first irradiation area A1 is larger than the intensity K2 of the second pulse light PL2 in the second irradiation area A2 Explained. However, the intensity K1 of the first pulse light PL1 in the first irradiation area A1 may be smaller than the intensity K2 of the second pulse light PL2 in the second irradiation area A2. In this case, the velocity of the second shock wave SW2 is faster than the velocity of the first shock wave SW1. Therefore, compared with the case where the second shock wave SW2 is not generated due to the interaction between the pressure waves facing each other across the first shock wave SW1 in the second shock wave SW2, the shock wave is an object under the first irradiation area A1. It propagates to the deep position of 5. As a result, a compressive residual stress field can be formed to a relatively deep position of the object 5.

Next, with reference to FIG. 5A, in the case where the strength K1 in the first irradiation area A1 is smaller than the strength K2 in the second irradiation area A2, the formation principle of the compressive residual stress field will be described in detail. . FIG. 5A is a diagram showing the formation principle of the compressive residual stress field.

As shown in FIG. 5A, in the vicinity of the boundary between the first irradiation area A1 and the second irradiation area A2, an oblique shock wave (pressure wave) WA1 and an oblique shock wave (pressure wave) WA2 are generated. Hereinafter, the oblique shock wave WA1 is described as a shock wave WA1, and the oblique shock wave WA2 is described as a shock wave WA2. The shock wave WA1 and the shock wave WA2 are parts of a second shock wave SW2 generated by the second pulse light PL2. In the vicinity of the boundary between the first irradiation area A1 and the second irradiation area A2, the shock wave WA1 and the shock wave WA2 face each other across the first irradiation area A1.

The shock wave WA1 has a velocity vector component Vh10 and a velocity vector component Vv1 in the vicinity of the boundary between the first irradiation region A1 and the second irradiation region A2. The velocity vector component Vh10 is substantially parallel to the surface 5a and faces the center C of the first irradiation area A1. The velocity vector component Vv1 is substantially perpendicular to the surface 5a and faces in the depth direction DP. The magnitude of the velocity vector component Vh10 is smaller than the magnitude of the velocity vector component Vv1. This is because the magnitude of the velocity vector component Vh10 is reduced by the first shock wave SW1 based on the first pulse light PL1.

On the other hand, the shock wave WA2 has a velocity vector component Vh20 and a velocity vector component Vv2 in the vicinity of the boundary between the first irradiation region A1 and the second irradiation region A2. The velocity vector component Vh20 is substantially parallel to the surface 5a and faces the center C of the first irradiation area A1. The velocity vector component Vv2 is substantially perpendicular to the surface 5a and is directed in the depth direction DP. The magnitude of the velocity vector component Vh20 is smaller than the magnitude of the velocity vector component Vv2. This is because the magnitude of the velocity vector component Vh20 is reduced by the first shock wave SW1 based on the first pulse light PL1.

The direction of the velocity vector component Vh20 is opposite to the direction of the velocity vector component Vh10. The magnitude of the velocity vector component Vh20 is substantially the same as the magnitude of the velocity vector component Vh10. The direction and the magnitude of the velocity vector component Vv2 are substantially the same as the direction and the magnitude of the velocity vector component Vv1, respectively.

The shock wave WA1 travels in the direction of a composite vector VR1 of the velocity vector component Vh10 and the velocity vector component Vv1. An angle θ10 between the composite vector VR1 and the surface 5a is an acute angle. On the other hand, shock wave WA2 proceeds in the direction of composite vector VR2 of velocity vector component Vh20 and velocity vector component Vv2. An angle θ20 between the composite vector VR2 and the surface 5a is an acute angle. The angle θ20 and the angle θ10 are substantially the same.

The composite vector VR1 and the composite vector VR2 are inclined with respect to the surface 5a so as to approach each other in the depth direction DP. Accordingly, the shock wave WA1 and the shock wave WA2 interfere with each other at a position substantially perpendicular to the depth direction DP with respect to the center C of the first irradiation area A1, so that a synthetic shock wave WAS is formed. That is, the shock wave WA1 and the shock wave WA2 cause the Mach reflection at the position of the depth DTP with respect to the center C of the first irradiation area A1, and the combined shock wave WAS is formed. Then, the synthetic shock wave WAS propagates in the depth direction DP. As a result, it is possible to form a compressive residual stress field to a relatively deep position of the object 5 by the synthetic shock wave WAS.

In particular, at a depth DTP where interference occurs, the pressure of the synthetic shockwave WAS is at a maximum. Therefore, as shown in FIGS. 4A and 4B, the compressive residual stress CTB has the peak value PV in the portion 53b located at the depth DTP.

Further, when the intensity K1 in the first irradiation area A1 is smaller than the intensity K2 in the second irradiation area A2, the combined shock wave WAS is formed, so the intensity K1 in the first irradiation area A1 is the second irradiation area. A compressive residual stress field can be formed to a deeper position as compared with the case where the strength K2 at A2 is larger.

Since the strength K1 in the first irradiation area A1 is smaller than the strength K2 in the second irradiation area A2, the ablation pressure P1 generated in the first irradiation area A1 is the ablation pressure P2 generated in the second irradiation area A2. Less than. Therefore, the peak pressure of the first shock wave SW1 becomes smaller than the peak pressure of the second shock wave SW2, and the velocity of the first shock wave SW1 is slower than the velocity of the second shock wave SW2. That is, the velocity of the second shock wave SW2 is faster than the velocity of the first shock wave SW1.

Here, even when the intensity K1 in the first irradiation region A1 is smaller than the intensity K2 in the second irradiation region A2, the intensity K1 in the first irradiation region A1 is larger than the intensity K2 in the second irradiation region A2. As in the case described above, the peak value PV of the compressive residual stress CTB applied to the object 5 based on the first pulse light PL1 and the second pulse light PL2 increases as the diameter DM1 of the first irradiation area A1 increases. It is located at a deep position with respect to the irradiation area A1.

The reason why the peak value PV of the compressive residual stress CTB is positioned deeper as the diameter DM1 is larger will be described by comparing FIG. 5A with FIG. 5B. FIG. 5 (b) is a diagram showing the formation principle of the compressive residual stress field.

As shown in FIGS. 5A and 5B, the value M2 of the diameter DM1 of the first irradiation area A1 shown in FIG. 5B is the diameter of the first irradiation area A1 shown in FIG. 5A. It is larger than the value M1 of DM1. Further, the intensity K1 in the first irradiation area A1 and the intensity K2 in the second irradiation area A2 are the same in the case of FIG. 5 (a) and the case of FIG. 5 (b). Therefore, in the case of FIG. 5A and the case of FIG. 5B, the directions and the sizes of the combined vector VR1 and the combined vector VR2 are the same.

As a result, when the diameter DM1 (= M2 in FIG. 5B) is large, the depth DTP (= T20 in FIG. 5B) at which the shock wave WA1 interferes with the shock wave WA2 is the diameter DM1 (= FIG. When M1) in a) is small, the depth is deeper than the depth DTP where the shock wave WA1 and the shock wave WA2 interfere with each other (= T10 in FIG. 5A). Therefore, when the diameter DM1 (= M2 in FIG. 5B) is large, the depth DTP at which the peak value PV of the compressive residual stress CTB is located is when the diameter DM1 (= M1 in FIG. 5A) is small. It is deeper than the depth DTP where the peak value PV of the compressive residual stress CTB is located. In other words, the peak value PV of the compressive residual stress CTB is located deeper as the diameter DM1 of the first irradiation area A1 is larger.

The absolute value of the peak value PV of the compressive residual stress CTB when the diameter DM1 is large is smaller than the absolute value of the peak value PV of the compressive residual stress CTB when the diameter DM1 is small. This is because the shock wave WA1 and the shock wave WA2 attenuate as the depth direction DP gets deeper, so the pressure of the synthetic shock wave WAS becomes smaller as the depth DTP where the shock wave WA1 and the shock wave WA2 interfere with each other becomes deeper.

Second Embodiment
A laser peening apparatus 100 according to Embodiment 2 of the present invention will be described with reference to FIGS. 6 to 8. The second embodiment is mainly different from the first embodiment in that the second embodiment generates the second pulsed light PL2 using a non-linear optical crystal. The differences between the second embodiment and the first embodiment will be mainly described below.

First, the configuration of a laser peening apparatus 100 according to the second embodiment will be described with reference to FIG. FIG. 6 is a view showing the laser peening apparatus 100. As shown in FIG. As shown in FIG. 6, the laser peening apparatus 100 includes a laser oscillator 11, an optical unit 13, a moving unit 15, and a control unit 17. The optical unit 13 includes a harmonic generation unit 21 and a pulse irradiation unit 3. The harmonic generation unit 21 includes an energy adjustment unit 23 and a non-linear optical crystal 25. The harmonic generation unit 21 and the laser oscillator 11 constitute a pulse generation unit 1. The pulse irradiation unit 3 includes a condensing lens 31.

The laser oscillator 11 generates pulse light PL and makes the pulse light PL incident on the harmonic generation unit 21. The pulsed light PL is a laser light. The laser oscillator 11 is, for example, a neodymium glass laser. Then, for example, the wavelength of the pulsed light PL is 1053 nm, the energy of the pulsed light PL is 300 J to 400 J, and the time width of the pulsed light PL is 10 ns.

The control unit 17 is, for example, a computer. The controller 17 controls the laser oscillator 11 so that the pulsed light PL has an asymmetrical shape. As a result, the laser oscillator 11 generates pulsed light PL whose shape on the time axis is asymmetric with respect to the peak. Specifically, the pulsed light PL has a first slope and a second slope which are inclined in different directions. On the time axis, the first slope is located forward of the second slope. The first slope is a gentler slope than the second slope.

The harmonic generation unit 21 generates the first pulse light PL1 and the second pulse light PL2 based on the pulse light PL. The shape of each of the first pulse light PL1 and the second pulse light PL2 is similar to the shape of the pulse light PL. The wavelength λ1 of the first pulse light PL1 is different from the wavelength λ2 of the second pulse light PL2.

Specifically, the pulsed light PL is incident on the nonlinear optical crystal 25 (executed in step S1 of FIG. 1B). Then, the nonlinear optical crystal 25 generates a second harmonic of the pulsed light PL (executed in step S1 of FIG. 1B). The second harmonic is the first pulse light PL1. The fundamental wave of the pulsed light PL is the second pulsed light PL2. For example, the wavelength λ1 of the fundamental wave is 1054 nm, and the wavelength λ2 of the second harmonic is 527 nm. Therefore, the wavelength λ1 of the first pulse light PL1 is shorter than the wavelength λ2 of the second pulse light PL2. The nonlinear optical crystal 25 is a type of second harmonic generation (SHG) crystal, and is, for example, a KDP (potassium dihydrogen phosphate) crystal.

The energy adjusting unit 23 adjusts the position of the nonlinear optical crystal 25 to adjust the ratio of the energy E1 of the first pulse light PL1 to the energy E2 of the second pulse light PL2. Specifically, the energy adjusting unit 23 adjusts the attitude of the nonlinear optical crystal 25 such that the energy E1 is smaller than the energy E2. For example, the energy adjusting unit 23 adjusts the attitude of the nonlinear optical crystal 25 such that the ratio (E1: E2) of the energy E1 to the energy E2 is 1: 9. As a result, the energy ratio of the first pulse light PL1 and the second pulse light PL2 is adjusted, and the light enters from the nonlinear optical crystal 25 to the condensing lens 31.

The condensing lens 31 irradiates the first pulse light PL1 to the surface 5a of the object 5 so as to form the first irradiation area A1 on the surface 5a of the object 5, and the second to the surface 5a of the object 5 The second pulse light PL2 is applied to the surface 5a of the object 5 so as to form an irradiation area A2 (executed in step S3 of FIG. 1B).

The control unit 17 controls the moving unit 15 so that the optical unit 13 moves along a direction substantially parallel to the optical axis AX of the laser oscillator 11. As a result, the moving unit 15 moves the optical unit 13 along a direction substantially parallel to the optical axis AX.

As described above with reference to FIG. 6, according to the second embodiment, as in the first embodiment, the intensity K1 of the first pulse light PL1 is larger than the intensity K2 of the second pulse light PL2. Therefore, the velocity of the first shock wave SW1 is larger than the velocity of the second shock wave SW2. As a result, due to the interference between the first shock wave SW1 and the second shock wave SW2, the first shock wave SW1 propagates to a deep position of the object 5, as compared to the case where the second shock wave SW2 is not generated. As a result, as in the first embodiment, it is possible to form a relatively thick compressive residual stress field inside the object 5. In addition, the second embodiment has the same effects as the first embodiment.

Further, according to the second embodiment, for example, the laser peening device 100 according to the second embodiment can be easily configured by introducing the nonlinear optical crystal 25 into a general laser peening device. As a result, a general laser peening apparatus can be easily functioned as the laser peening apparatus 100 capable of forming a relatively thick compressive residual stress field inside the object 5.

Furthermore, according to the second embodiment, by setting the wavelength λ1 of the first pulse light PL1 shorter than the wavelength λ2 of the second pulse light PL2, the intensity K1 of the first pulse light PL1 is greater than the intensity K2 of the second pulse light PL2. Can easily be enlarged. Further, by making the wavelength λ1 shorter than the wavelength λ2, the ablation pressure P1 based on the first pulse light PL1 can be easily made larger than the ablation pressure P2 based on the second pulse light PL2. As a result, it is possible to easily generate the first shock wave SW1 having a velocity larger than the velocity of the second shock wave SW2.

Next, the details of the optical unit 13 will be described with reference to FIG. FIG. 7 is a schematic cross-sectional view showing the optical unit 13.

As shown in FIG. 7, the harmonic wave generator 21 further includes a crystal holder 27 and a support 29. The crystal holder 27 holds the nonlinear optical crystal 25. The support portion 29 supports the non-linear optical crystal 25 via the crystal holder 27 so that the non-linear optical crystal 25 can swing.

The energy adjusting unit 23 of the harmonic generating unit 21 includes a first micrometer 23 a and a second micrometer 23 b. The posture of the nonlinear optical crystal 25 is set to a specific posture by the first micrometer 23 a and the second micrometer 23 b, and phase matching is performed on the nonlinear optical crystal 25. Then, the posture of the nonlinear optical crystal 25 is changed to a specific posture by the first micrometer 23a, and the ratio of the energy E1 of the first pulse light PL1 to the energy E2 of the second pulse light PL2 is adjusted.

The pulse irradiation unit 3 further includes a lens holder 33. The lens holder 33 holds the condenser lens 31. The lens holder 33 is fixed to the support 29. The condensing lens 31 is, for example, a convex lens.

The condensing lens 31 condenses the first pulse light PL 1 and the second pulse light PL 2 on the surface 5 a of the object 5. Specifically, the wavelength of the first pulse light PL1 is shorter than the wavelength of the second pulse light PL2. Therefore, the condensing lens 31 refracts the first pulse light PL1 toward the optical axis AX at an angle larger than that of the second pulse light PL2. As a result, the first pulsed light PL1 is irradiated from the condenser lens 31 to the surface 5a of the object 5 so that the first irradiation area A1 is formed, and the second irradiation area A2 is formed. Two-pulse light PL2 is emitted. According to the second embodiment, by making the first pulsed light PL1 and the second pulsed light PL2 incident on the condenser lens 31, the first irradiation area A1 and the second irradiation area A2 can be easily formed on the surface 5a of the object 5 It can be formed into

By adjusting the focal length of the condenser lens 31, the intensity K1 of the first pulse light PL1 and the intensity K2 of the second pulse light PL2, and the area of the first irradiation area A1 (for example, the diameter DM1) and the second irradiation area The area of A2 (for example, the diameter DM2) can be easily controlled. For example, the diameter DM1 of the first irradiation area A1 is about 1 mm, and the diameter DM2 of the second irradiation area A2 is about 10 mm. For example, the intensity K1 of the first pulse light PL1 is 10 ¹¹ W / cm ² , and the intensity K2 of the second pulse light PL2 is 10 ¹⁰ W / cm ² .

The moving unit 15 includes a linear stage 41 and a motor 43. The optical unit 13 is installed on the linear stage 41. Then, the linear stage 41 is driven by the motor 43 and moves along a direction substantially parallel to the optical axis AX. Therefore, the optical unit 13 can be moved along a direction substantially parallel to the optical axis AX to change the distance between the condenser lens 31 and the object 5. As a result, the intensity K1 of the first pulse light PL1 and the intensity K2 of the second pulse light PL2 and the area of the first irradiation area A1 (for example, diameter DM1) and the area of the second irradiation area A2 (for example, diameter DM2) can be easily Can be controlled.

In the second embodiment, the moving unit 15 sets the position of the optical unit 13 such that the surface 5 a of the object 5 is closer to the focusing lens 31 than the focal length of the focusing lens 31. As a result, the intensity K1 of the first pulse light PL1 becomes larger than the intensity K2 of the second pulse light PL2.

When the compressive residual stress field is formed over a wide range of the object 5, the object 5 is directed along the direction DA crossing the optical axis AX (specifically, the direction DA substantially orthogonal to the optical axis AX) While moving, the first pulsed light PL1 and the second pulsed light PL2 are applied to the surface 5a of the object 5. Alternatively, while moving the optical unit 13 along the direction DA, the surface of the object 5 is irradiated with the first pulse light PL1 and the second pulse light PL2.

Next, with reference to FIG. 8, the intensity K1 of the first pulse light PL1 and the intensity K2 of the second pulse light will be described. FIG. 8 is a graph showing the relationship between the ablation pressure and the intensity K1 of the first pulse light PL1 and the intensity K2 of the second pulse light. In FIG. 8, the vertical axis represents ablation pressure (Gigapascal: GPa), and the horizontal axis represents intensity (W / cm ² ) of pulsed light at the surface 5 a of the object 5.

As shown in FIG. 8, for example, the intensity K1 of the first pulse light PL1 is on the order of 10 ¹¹ (W / cm ² ) (corresponding to the area B1). On the other hand, for example, the intensity K2 of the second pulse light PL2 is on the order (corresponding to the area B2) of about 10 ¹⁰ (W / cm ² ).

Then, in the first irradiation area A1, an ablation pressure P1 corresponding to the intensity K1 of about 10 ¹¹ (W / cm ² ) is generated. On the other hand, in the second irradiation area A2, an ablation pressure P2 corresponding to the intensity K2 on the order of approximately 10 ¹⁰ (W / cm ² ) is generated. Therefore, the peak pressure of the first shock wave SW1 generated in the first irradiation area A1 is larger than the peak pressure of the second shock wave SW2 generated in the second irradiation area A2. As a result, the velocity of the first shock wave SW1 becomes larger than the velocity of the second shock wave SW2.

In addition, since the ablation pressures P1 and P2 of 10 ⁰ (GPa) or more are generated by each of the first pulse light PL1 and the second pulse light PL2, a compressive residual stress field can be easily formed inside the object 5. In particular, since the ablation pressure P1 of 10 ¹ (GPa) or more is generated by the first pulse light PL1, a compressive residual stress field can be more easily formed inside the object 5.

The intensity K1 of the first pulse light PL1 and the intensity K2 of the second pulse light PL2 are merely examples, and the intensities K1 and K2 are not particularly limited as long as the ablation pressure is generated.

As described above, in the description of FIGS. 6 to 8, the intensity K1 of the first pulse light PL1 in the first irradiation area A1 is larger than the intensity K2 of the second pulse light PL2 in the second irradiation area A2. However, the intensity K1 of the first pulse light PL1 in the first irradiation area A1 may be smaller than the intensity K2 of the second pulse light PL2 in the second irradiation area A2.

(Embodiment 3)
A laser peening apparatus 100A according to a third embodiment of the present invention will be described with reference to FIGS. 9 (a) to 12. The third embodiment mainly differs from the first embodiment in that the third embodiment does not irradiate the first irradiation region A1 with the first pulse light PL1. The differences between the third embodiment and the first embodiment will be mainly described below.

First, the configuration and operation of the laser peening apparatus 100A according to the third embodiment will be described with reference to FIGS. 9A to 9C.

Fig.9 (a) is a figure which shows 100 A of laser peening apparatuses. FIG. 9B is a flowchart showing a laser peening method performed by the laser peening apparatus 100A. FIG.9 (c) is a figure which shows non-irradiation area | region W1 and irradiation area W2 by laser peening apparatus 100A.

As shown in FIG. 9A, the laser peening apparatus 100A performs laser peening on the object 5. The laser peening apparatus 100A includes a pulse generation unit 1A and a pulse irradiation unit 3A. Then, as shown in FIG. 9B, the laser peening apparatus 100A executes the laser peening method. The laser peening method includes steps S21 and S23.

In step S21, the pulse generation unit 1 generates pulsed light PLD. The pulsed light PLD is a laser light. The pulsed light PLD has a substantially annular cross section.

Next, as shown in FIGS. 9 (b) and 9 (c), in step S23, the pulse irradiation unit 3A covers the irradiation area W2 surrounding the non-irradiation area W1 (predetermined area) of the surface 5a of the object 5. The pulsed light PLD is applied to the surface 5 a of the object 5 so as to form the surface 5 a of the object 5.

The non-irradiation area W1 has a substantially circular shape. The shape of the non-irradiation area W1 is, for example, the same as the shape of the first irradiation area A1 shown in FIG. 1 (c). However, the pulse light PLD is not irradiated to the non-irradiation area W1.

The irradiation area W2 surrounds the non-irradiation area W1. That is, the non-irradiation area W1 is surrounded by the irradiation area W2. The irradiation area W2 has a substantially annular shape surrounding the non-irradiation area W1. The shape of the irradiation area W2 is, for example, the same as the shape of the second irradiation area A2 shown in FIG. 1 (c). The diameter DM2 of the irradiation area W2 is larger than the diameter DM1 of the non-irradiation area W1. The diameter DM1 of the non-irradiated area W1 corresponds to an example of the “diameter of the non-irradiated area”.

As described above with reference to FIGS. 9A to 9C, according to the third embodiment, the pulsed light PLD is irradiated to the irradiation area W2. Therefore, a shock wave (hereinafter, sometimes referred to as “shock wave SW”) from the irradiation area W2 to the inside of the object 5 is generated. On the other hand, the pulsed light PLD is not irradiated to the non-irradiation area W1. Therefore, among the shock waves SW generated by the pulsed light PLD, a compressive residual stress field can be formed to a relatively deep position of the object 5 by the interaction of the pressure waves facing each other across the lower area of the non-irradiation area W1. . In other words, it is possible to form a relatively thick compressive residual stress field inside the object 5. In addition, the third embodiment has the same effects as the first embodiment.

In other words, in the third embodiment, the object 5 is modified by forming a compressive residual stress field in the object 5 by the laser peening method described with reference to FIG. 9B. Therefore, in the third embodiment, there is provided a modified product manufacturing method in which the target 5 is modified by the laser peening method described with reference to FIG. Further, the reformed product 51 in the case where the object 5 is a metal is the metal material 51A.

Next, the object 5 in which the compressive residual stress field is formed will be described with reference to FIGS. 10 (a) and 10 (b). FIG. 10A is a graph showing the residual stress field formed on the object 5 by the laser peening apparatus 100A. In FIG. 10 (a), the vertical axis indicates residual stress (megapascals: MPa), and the horizontal axis indicates depths (micrometers: mm) from the surface 5a of the object 5. FIG. 10 (b) is a schematic cross-sectional view showing the object 5 modified by the laser peening apparatus 100A.

As shown to Fig.10 (a), residual stress CT generate | occur | produces the inside of the target object 5 to which pulsed light PLD of cross-sectional view substantially annular shape was irradiated. FIG. 10A shows the residual stress CT below the center C of the non-irradiation area W1. A positive value residual stress CT indicates a tensile residual stress CTA, and a negative value residual stress CT indicates a compressive residual stress CTB.

Further, as shown in FIG. 10B, the object 5 (specifically, the reformed product 51 or the metal material 51A) includes the main body 53. The main body 53 has a surface 53a and a portion 53b. The surface 53a corresponds to the surface 5a. The surface 53a has a non-irradiation area W1 of the pulsed light PLD and an irradiation area W2 of the pulsed light PLD. The portion 53 b is located at a position distant from the surface 53 a in the depth direction DP. Specifically, the portion 53b is located at a position substantially perpendicular to the depth direction DP with respect to the center C of the non-irradiation area W1. That is, the portion 53b is located at the depth DTP with respect to the center C of the non-irradiation area W1.

In the third embodiment, the depth direction DP is substantially perpendicular to the surface 53a and indicates a direction away from the surface 53a. Specifically, the depth direction DP indicates the direction in which the depth increases with respect to the non-irradiation area W1. In the present specification, the lower side of the non-irradiation area W1 indicates the depth direction DP side with respect to the non-irradiation area W1, and the lower side of the center C of the non-irradiation area W1 is the center C of the non-irradiation area W1. The depth direction DP side is shown.

As shown in FIGS. 10A and 10B, in the portion 53b, the compressive residual stress CTB has a peak value PV. The peak value PV indicates the maximum value of the absolute value of the compressive residual stress CTB. The compressive residual stress CTB is attenuated while repeatedly decreasing and increasing from the peak value PV in the depth direction DP. That is, the compressive residual stress CTB is attenuated while being repeatedly decreased and increased from the portion 53 b in the depth direction DP. Therefore, according to the third embodiment, compared with the case where the compressive residual stress monotonously decreases, the compressive residual stress CTB can be generated over a deep range in the depth direction DP. That is, it is possible to form a relatively thick compressive residual stress field. The reason that the compressive residual stress CTB is attenuated while being repeatedly decreased and increased is that the compressive residual stress CTB is generated due to the interference between mutually opposing pressure waves in the shock wave SW.

Next, with reference to FIGS. 10A and 10B, the relationship between the diameter DM1 of the non-irradiated area W1 and the peak value PV of the compressive residual stress CTB will be described. The peak value PV of the compressive residual stress CTB applied to the object 5 based on the pulsed light PLD having a substantially annular shape in a sectional view is deeper than the non-irradiation area W1 as the diameter DM1 of the non-irradiation area W1 is larger. Located in Therefore, according to the third embodiment, by adjusting the diameter DM1 of the non-irradiation area W1, the position in the depth direction DP of the peak value PV of the compressive residual stress CTB can be controlled. The position in the depth direction DP of the peak value PV indicates the depth DTP.

Specifically, as shown in FIGS. 9A and 9B, step S21 includes step S211. Then, in step S211, the pulse generation unit 1A controls the position (depth DTP) in the depth direction DP of the peak value PV of the compressive residual stress CTB by adjusting the diameter DM1 of the non-irradiation area W1. Specifically, the diameter DM1 of the non-irradiation area W1 is set by adjusting the optical system of the pulse generation unit 1A. Therefore, in step S23, the pulse irradiation unit 3A irradiates the surface 5a of the object 5 with the pulsed light PLD so as to form an irradiation region W2 surrounding the non-irradiation region W1 having the diameter DM1 set in step S211. . According to the third embodiment, as the laser peening method includes step S211, the position in the depth direction DP of the peak value PV of the compressive residual stress CTB can be controlled.

Next, with reference to FIG. 11 (a), the formation principle of the compressive residual stress field will be described in detail. FIG. 11A is a diagram showing the formation principle of the compressive residual stress field. As shown in FIG. 11A, an oblique shock wave (pressure wave) WA1 and an oblique shock wave (pressure wave) WA2 are generated in the vicinity of the boundary between the non-irradiation area W1 and the irradiation area W2. Hereinafter, the oblique shock wave WA1 is described as a shock wave WA1, and the oblique shock wave WA2 is described as a shock wave WA2. The shock wave WA1 and the shock wave WA2 are parts of the shock wave SW generated by the pulsed light PLD. In the vicinity of the boundary between the non-irradiation area W1 and the irradiation area W2, the shock wave WA1 and the shock wave WA2 face each other across the non-irradiation area W1.

The shock wave WA1 has a velocity vector component Vh1 and a velocity vector component Vv1 in the vicinity of the boundary between the non-irradiation area W1 and the irradiation area W2. The velocity vector component Vh1 is substantially parallel to the surface 5a and faces the center C of the non-irradiation area W1. The velocity vector component Vv1 is substantially perpendicular to the surface 5a and faces in the depth direction DP. The magnitude of the velocity vector component Vh1 is substantially the same as the magnitude of the velocity vector component Vv1. Since the pulse light PLD is not irradiated to the non-irradiation area W1, no shock wave is generated from the non-irradiation area W1 to reduce the velocity vector component Vh1.

On the other hand, shock wave WA2 has velocity vector component Vh2 and velocity vector component Vv2 in the vicinity of the boundary between non-irradiation area W1 and irradiation area W2. The velocity vector component Vh2 is substantially parallel to the surface 5a and faces the center C of the non-irradiation area W1. The velocity vector component Vv2 is substantially perpendicular to the surface 5a and is directed in the depth direction DP. The magnitude of the velocity vector component Vh2 is substantially the same as the magnitude of the velocity vector component Vv2. Since the pulse light PLD is not irradiated to the non-irradiation area W1, no shock wave for reducing the velocity vector component Vh2 is generated from the non-irradiation area W1.

The direction of the velocity vector component Vh2 is opposite to the direction of the velocity vector component Vh1. The magnitude of the velocity vector component Vh2 is substantially the same as the magnitude of the velocity vector component Vh1. The direction and the magnitude of the velocity vector component Vv2 are substantially the same as the direction and the magnitude of the velocity vector component Vv1, respectively.

The shock wave WA1 travels in the direction of a composite vector VR1 of the velocity vector component Vh1 and the velocity vector component Vv1. An angle θ1 between the combined vector VR1 and the surface 5a is an acute angle. Specifically, the angle θ1 is approximately 45 degrees. On the other hand, shock wave WA2 proceeds in the direction of composite vector VR2 of velocity vector component Vh2 and velocity vector component Vv2. An angle θ2 between the combined vector VR2 and the surface 5a is an acute angle. Specifically, the angle θ2 is approximately 45 degrees. The angle θ2 and the angle θ1 are substantially the same.

The composite vector VR1 and the composite vector VR2 are inclined with respect to the surface 5a so as to approach each other in the depth direction DP. Therefore, the shock wave WA1 and the shock wave WA2 interfere with each other at a position substantially perpendicular to the depth direction DP with respect to the center C of the non-irradiation area W1, and a synthetic shock wave WAS is formed. That is, the shock wave WA1 and the shock wave WA2 cause the Mach reflection at the position of the depth DTP with respect to the center C of the non-irradiation area W1, and the combined shock wave WAS is formed. Then, the synthetic shock wave WAS propagates in the depth direction DP. As a result, it is possible to form a compressive residual stress field to a relatively deep position of the object 5 by the synthetic shock wave WAS.

In particular, at a depth DTP where interference occurs, the pressure of the synthetic shockwave WAS is at a maximum. Therefore, in the portion 53b located at the depth DTP, the compressive residual stress CTB has the peak value PV.

Further, in the third embodiment, since the non-irradiation area W1 is present, the depth DTP at which the synthetic shock wave WAS is generated is shallower compared to the case where the first irradiation area A1 is present (FIG. 5A). That is, the angle θ1 is smaller than the angle θ10 (FIG. 5A), and the angle θ2 is smaller than the angle θ20 (FIG. 5A). Therefore, in the third embodiment, the pressures of the shock wave WA1 and the shock wave WA2 at the time of interference are larger than those in the case where the first irradiation area A1 is present. That is, since the shock wave WA1 and the shock wave WA2 are attenuated as they get deeper in the depth direction DP, the pressure of the synthetic shock wave WAS increases as the depth DTP at which the shock wave WA1 interferes with the shock wave WA2 decreases. Therefore, in the third embodiment, compared with the case where the first irradiation area A1 is present, the synthetic shock wave WAS can be advanced to a further deep position, and a compressive residual stress field can be formed to a further deep position.

Furthermore, in the third embodiment, the angle θ1 is approximately 45 degrees, and the angle θ2 is approximately 45 degrees. Therefore, the depth DTP of the portion 53b with respect to the non-irradiated area W1 is substantially equal to the radius R of the non-irradiated area W1. As a result, by adjusting the radius R of the non-irradiation area W1, the depth DTP of the portion 53b having the peak value PV of the compressive residual stress CTB can be accurately controlled.

In other words, the radius R of the non-irradiation area W1 is substantially equal to the depth DTP for the non-irradiation area W1 of the peak value PV of the compressive residual stress CTB applied to the object 5 by the shock wave SW based on the pulsed light PLD. . Therefore, according to the third embodiment, the depth DTP of the peak value PV of the compressive residual stress CTB can be easily estimated from the radius R of the non-irradiation area W1.

Next, the reason why the peak value PV of the compressive residual stress CTB is positioned deeper as the diameter DM1 is larger will be described by comparing FIG. 11 (a) with FIG. 11 (b). FIG. 11 (b) is a view showing the formation principle of the compressive residual stress field.

As shown in FIGS. 11 (a) and 11 (b), the value M2 of the diameter DM1 of the non-irradiated area W1 shown in FIG. 11 (b) is the value DM2 of the non-irradiated area W1 shown in FIG. Greater than the value M1. Further, the intensity of the pulsed light PLD in the irradiation area W2 is the same in the case of FIG. 11 (a) and in the case of FIG. 11 (b). Therefore, in the case of FIG. 11A and the case of FIG. 11B, the directions and the sizes of the combined vector VR1 and the combined vector VR2 are the same.

As a result, when the diameter DM1 (= M2 in FIG. 11B) is large, the depth DTP (= T20 in FIG. 11B) at which the shock wave WA1 interferes with the shock wave WA2 is the diameter DM1 (= FIG. When M1) in a) is small, the depth is deeper than the depth DTP where the shock wave WA1 and the shock wave WA2 interfere with each other (= T10 in FIG. 11A). Therefore, when the diameter DM1 (= M2 in FIG. 11B) is large, the depth DTP at which the peak value PV of the compressive residual stress CTB is located is when the diameter DM1 (= M1 in FIG. 11A) is small. It is deeper than the depth DTP where the peak value PV of the compressive residual stress CTB is located. In other words, the peak value PV of the compressive residual stress CTB is positioned deeper as the diameter DM1 of the non-irradiation area W1 is larger.

For the same reason as in the first embodiment described with reference to FIGS. 5A and 5B, the absolute value of the peak value PV of the compressive residual stress CTB when the diameter DM1 is large is equal to the diameter DM1. It is smaller than the absolute value of the peak value PV of the compressive residual stress CTB in the small case.

Next, the details of the laser peening apparatus 100A will be described with reference to FIG. FIG. 12 is a view showing the details of the laser peening apparatus 100A. As shown in FIG. 12, in the laser peening apparatus 100A, the pulse generation unit 1A includes a laser oscillator 71 and a diameter setting unit 73. The pulse irradiation unit 3A includes a condensing lens 61.

The configuration of the laser oscillator 71 is the same as the configuration of the laser oscillator 11 shown in FIG. The laser oscillator 71 generates pulse light PL having a substantially circular cross-sectional view, and causes the pulse light PL to enter the diameter setting unit 73. Specifically, the laser oscillator 71 causes the pulse light PL to be incident on the diameter setting unit 73 through an optical system (not shown) including a lens, a mirror and the like.

The diameter setting unit 73 sets the diameter DM1 of the non-irradiation area W1. Specifically, the diameter setting unit 73 includes a substrate 73a and a light blocking unit 73b. The substrate 73a transmits the pulsed light PL. The substrate 73a is, for example, transparent. The substrate 73a is made of, for example, glass or synthetic resin. The light blocking unit 73 b blocks the pulsed light PL. As a result, the diameter setting unit 73 emits the pulse light PLD having a substantially annular shape in cross section toward the condensing lens 61. The light blocking portion 73b is attached to, for example, the surface of the substrate 73a. The light blocking portion 73 b is black, for example, and absorbs the pulse light PL and does not transmit the pulse light PL. The light blocking portion 73 b is made of, for example, metal or synthetic resin. The light blocking portion 73 b has, for example, a substantially circular shape. The shape of the light blocking portion 73b is similar to the shape of the non-irradiation area W1.

When the diameter setting unit 73 includes the light blocking unit 73 b, the pulse light PLD incident on the condensing lens 61 has a substantially annular shape in cross section.

The condensing lens 61 irradiates the surface 5 a of the object 5 with the pulsed light PLD so as to form an irradiation area W 2 surrounding the non-irradiation area W 1 of the surface 5 a of the object 5. In particular, in the third embodiment, the diameter setting unit 73, the condenser lens 61, and the object 5 are disposed so as to satisfy 1 / f = (1 / La) + (1 / Lb). As a result, the laser peening apparatus 100A can form the non-irradiation area W1 similar to the light blocking portion 73b on the surface 5a of the object 5 with high accuracy. That is, the laser peening apparatus 100A can transfer the image of the light blocking portion 73b to the surface 5a of the object 5 and form the non-irradiation area W1 with high accuracy. “F” indicates the focal length of the condenser lens 61. “La” indicates the distance between the diameter setting unit 73 and the condenser lens 61. “Lb” indicates the distance between the focusing lens 61 and the object 5.

As long as the non-irradiated area W1 of the surface 5a of the object 5 can be formed, the method of generating the pulsed light PLD having a substantially annular shape in cross section is not particularly limited.

For example, the diameter setting unit 73 may include a transmissive spatial light modulator (SLM) instead of the substrate 73 a and the light blocking unit 73 b. The SLM includes a plurality of pixels arranged in one or two dimensions. Then, the SLM performs phase modulation on the pulse light PL for each pixel. Specifically, the SLM performs phase modulation so that the pulse light PL does not emit from the pixels of the area corresponding to the non-irradiation area W1, and the pulse light PL emits from the pixels of the area corresponding to the irradiation area W2. Do.

For example, the diameter setting unit 73 may include an optical system that generates a Laguerre-Gaussian beam from the pulsed light PL, instead of the substrate 73a and the light blocking unit 73b. Then, the diameter setting unit 73 may emit the Laguerre-Gaussian beam as the pulsed light PLD. Alternatively, the laser oscillator 71 may generate a Laguerre-Gaussian beam and emit the Laguerre-Gaussian beam as pulsed light PLD. In this case, the diameter setting unit 73 may not be provided.

In the first embodiment described with reference to FIGS. 1A to 1C, the intensity K1 of the first pulse light PL1 in the first irradiation area A1 is the second pulse in the second irradiation area A2. In the case where the intensity K2 of the light PL2 is made larger, the laser peening apparatus 100A described with reference to FIG. 12 can be used.

However, in this case, for example, instead of the light blocking part 73b, a member that transmits the pulse light PL (hereinafter, referred to as "member MB1") is attached to the substrate 73a. The light transmittance of the member MB1 is higher than the light transmittance of the substrate 73a. As a result, the first irradiation area A1 is formed on the surface 5a of the object 5 corresponding to the member MB1.

Alternatively, in this case, for example, the diameter setting unit 73 includes a transmission-type SLM instead of the substrate 73a and the light blocking unit 73b. Then, in the SLM, the intensity K1 of the light (first pulse light PL1) emitted from the pixel in the region corresponding to the first irradiation region A1 in the pulse light PL is from the pixel in the region corresponding to the second irradiation region A2. The phase modulation is performed to be larger than the intensity K2 of the emitted light (second pulse light PL2).

In the first embodiment described with reference to FIGS. 5A and 5B, the intensity K1 of the first pulse light PL1 in the first irradiation area A1 is the second pulse in the second irradiation area A2. When making it smaller than intensity K 2 of light PL 2, the laser peening apparatus 100 A described with reference to FIG. 12 can be used.

However, in this case, for example, instead of the light blocking part 73b, a member that transmits the pulsed light PL (hereinafter, referred to as "member MB2") is attached to the substrate 73a. The light transmittance of the member MB2 is lower than the light transmittance of the substrate 73a. As a result, the first irradiation area A1 is formed on the surface 5a of the object 5 corresponding to the member MB2.

Alternatively, in this case, for example, the diameter setting unit 73 includes a transmission-type SLM instead of the substrate 73a and the light blocking unit 73b. Then, in the SLM, the intensity K1 of the light (first pulse light PL1) emitted from the pixel in the region corresponding to the first irradiation region A1 in the pulse light PL is from the pixel in the region corresponding to the second irradiation region A2. Phase modulation is performed so as to be smaller than the intensity K2 of the emitted light (second pulse light PL2).

Alternatively, in this case, for example, the diameter setting unit 73 includes an optical system that generates a Laguerre-Gaussian beam from the pulsed light PL, instead of the substrate 73a and the light blocking unit 73b. Then, the diameter setting unit 73 controls the second irradiation area A2 to be irradiated with the intensity K1 of the light (first pulse light PL1) irradiated to the first irradiation area A1 among the Laguerre-Gaussian beams (second The Laguerre-Gaussian beam is emitted so as to be smaller than the intensity K2 of the pulsed light PL2). Also, the laser oscillator 71 may generate such a Laguerre-Gaussian beam. In this case, the diameter setting unit 73 may not be provided.

Next, the present invention will be specifically described based on examples, but the present invention is not limited by the following examples.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. 6, 7, and 13 to 17. In the first example, the laser peening apparatus 100 according to the second embodiment described with reference to FIGS. 6 and 7 was used. The intensity K1 of the first pulse light PL1 in the first irradiation area A1 was larger than the intensity K2 of the second pulse light PL2 in the second irradiation area A2. The object 5 was stainless steel (SUS304). The laser oscillator 11 was a neodymium glass laser. The wavelength of the pulsed light PL was 1054 nm, the energy of the pulsed light PL was 350 J, and the time width of the pulsed light PL was 10 ns. The target 5 did not have the specific layer LY, and was the target TA itself. The first pulse light PL1 and the second pulse light PL2 were directly irradiated to the surface 5a of the object 5 in vacuum.

The wavelength of the first pulse light PL1 (second harmonic) was 527 nm. The energy of the first pulse light PL1 in the first irradiation region A1 was 7.53 (J). The intensity K1 of the first pulse light PL1 in the first irradiation area A1 was 365.7 (GW / cm ² ). The position and focal length of the condenser lens 31 were adjusted so that the diameter DM1 of the first irradiation area A1 was approximately 1 mm.

The wavelength of the second pulse light PL2 (fundamental wave) was 1054 nm. The energy of the second pulse light PL2 in the second irradiation region A2 was 336.4 (J). The intensity K2 of the second pulse light PL2 in the second irradiation area A2 was 53 (GW / cm ² ). The position and focal length of the condenser lens 31 were adjusted so that the diameter DM2 of the second irradiation area A2 was approximately 10 mm.

First, the compressive residual stress field formed by the laser peening apparatus 100 according to the first embodiment will be described with reference to FIG.

FIG. 13 is a view showing a residual stress field according to the first embodiment. In FIG. 13, the vertical axis indicates residual stress (megapascals: MPa), and the horizontal axis indicates depths from the surface 5 a of the object 5 (micrometers: μm).

As shown in FIG. 13, the residual stress formed inside the object 5 was measured by the sin ² φ method using X-ray diffraction. Specifically, the residual stress under the center C of the first irradiation area A1 was measured. The residual stress of positive value showed the residual stress of tensile (tensile residual stress) and the residual stress of negative value showed the residual stress of compressive (compression residual stress). The X-ray diffraction apparatus was a "D8 Discover with GADDS (General Area Detector Diffraction System)" manufactured by Bruker.

The compressive residual stress existed to a depth close to 2000 μm (2 mm). That is, it could be confirmed that the compressive residual stress field was formed to a depth close to 2000 μm. Specifically, the peak value PV of compressive residual stress was located at a depth of about 500 μm. And it could be confirmed that the compressive residual stress was attenuated while repeating attenuation and increase from the peak value PV in the depth direction DP. Specifically, after the compressive residual stress exceeds a depth of about 1000 μm (1 mm), it does not decay monotonously with respect to the depth direction DP, and repeats attenuation and increase with respect to the depth direction DP. While I was able to confirm that it was gradually decaying. The reason why the compressive residual stress did not decay monotonously could be presumed to be the effect of the interference between the first shock wave SW1 and the second shock wave SW2.

In the first embodiment, even when the object 5 does not have the specific layer LY, the compressive residual stress field can be formed to a depth on the order of millimeters.

Next, the first irradiation area A1 and the second irradiation area A2 formed by the laser peening apparatus 100 according to the first embodiment will be described with reference to FIGS. 14 (a) to 15 (b). FIGS. 14 (a) to 15 (b) show the results of measuring the roughness of the surface 5a of the object 5 using a laser displacement meter. The closer the color is to black, the larger the roughness of the surface 5a. That is, the closer the color is to black, the deeper the region is. The laser displacement meter was "KS-1100" manufactured by Keyence Corporation.

FIG. 14A is a view showing a first irradiation area A1 and a second irradiation area A2. FIG. 14B is a diagram showing a part of the first irradiation area A1 in an enlarged manner. FIG. 14C is an enlarged view of a part of the second irradiation area A2.

As shown in FIGS. 14 (a) to 14 (c), the diameter DM1 of the first irradiation area A1 was approximately 1 mm. The roughness of the first irradiation area A1 was larger than the roughness of the second irradiation area A2. Therefore, it was confirmed that the first irradiation region A1 was formed by the large first pulse light PL1 having the intensity K1. For the same reason, it was possible to infer that a large ablation pressure P1 was generated in the first irradiation area A1, and a large first shock wave SW1 having a large speed was generated.

On the other hand, the diameter DM2 of the second irradiation area A2 was approximately 10 mm. The roughness of the second irradiation area A2 was smaller than the roughness of the first irradiation area A1. Therefore, it could be confirmed that the second irradiation area A2 was formed by the small second pulse light PL2 having the intensity K2. In addition, it is estimated that an ablation pressure P2 smaller than the ablation pressure P1 of the first irradiation region A1 is generated in the second irradiation region A2, and a second shock wave SW2 having a velocity smaller than the velocity of the first shock wave SW1 is generated. did it.

FIG. 15A shows the depths of the first irradiation area A1 and the second irradiation area A2. FIG. 15 (a) shows the depth in a cross section along the line XV-XV in FIG. 14 (a). In FIG. 15 (a), the vertical axis indicates the depth (μm) from the surface 5a of the object 5, and the horizontal axis indicates the position (mm). FIG. 15B is a perspective view showing the first irradiation area A1 and the second irradiation area A2.

As shown to Fig.15 (a), the position of 5 mm showed the center C of 1st irradiation area | region A1. The depth of the deepest part of the first irradiation area A1 was about 7 μm. Therefore, it could be confirmed that the damage of the object 5 due to the first pulse light PL1 was hardly occurred. Moreover, the depth of the deepest part of 2nd irradiation area | region A2 was about 2 micrometers. Therefore, it could be confirmed that the damage of the object 5 by the second pulse light PL2 was hardly occurred.

As shown in FIG. 15B, a shallow portion was observed near the center C of the first irradiation area A1. It was estimated that the shallow portion was generated due to the interference between the first shock wave SW1 and the second shock wave SW2. That is, the occurrence of the shallow portion indicates that the first shock wave SW1 and the second shock wave SW2 interfere with each other.

Next, with reference to FIGS. 16A and 16B, the first pulse light PL1 and the second pulse light PL2 generated by the laser peening apparatus 100 according to the first embodiment will be described.

FIG. 16A shows the first pulse light PL1. FIG. 16B is a diagram showing the second pulse light PL2. In FIG. 16A and FIG. 16B, the vertical axis represents the intensity (arbitrary unit) of pulsed light, and the horizontal axis represents time (ns). The first pulse light PL 1 and the second pulse light PL 2 were measured by the power sensor on the surface 5 a of the object 5. The power sensor was a "biplanar phototube R1328U-51 (second pulsed light PL2) R1328U-52 (first pulsed light PL1)" manufactured by Hamamatsu Photonics. In FIG. 16A and FIG. 16B, the scales on the vertical axis do not match.

As shown in FIG. 16A, the shape of the first pulse light PL1 was asymmetrical with respect to the peak. The first pulse light PL1 has a first slope SL1 and a second slope SL2. The first slope SL1 has a gentle slope than the second slope SL2. The time width of the first pulse light PL1 was 10 ns.

As shown in FIG. 16B, the shape of the second pulse light PL2 was asymmetrical with respect to the peak. The second pulse light PL2 has the first slope SL12 and the second slope SL22. The first slope SL12 has a gentler slope than the second slope SL22. The time width of the second pulse light PL2 was 10 ns.

As shown in FIGS. 16A and 16B, the shape of the first pulse light PL1 was similar to the shape of the second pulse light PL2. It can be inferred that both the first pulse light PL1 and the second pulse light PL2 are generated from the pulse light PL. It can be estimated that the shape of the pulsed light PL is similar to the shape of the first pulsed light PL1.

Next, the particle velocity generated in the object 5 by the laser peening apparatus 100 according to the first embodiment will be described with reference to FIGS. 3 (b), 16 (a) and 17. The particle velocity is the velocity of a particle located at a position of interest inside the object 5. Particle velocity is one of the parameters representing shock wave pressure. The particle velocity indicated the velocity of the particles below the first irradiation area A1. Particle velocity was measured using VISAR (Velocity Interferometer System for Any Reflector method).

FIG. 17 is a graph showing the relationship between particle velocity and time. In FIG. 17, the vertical axis represents particle velocity (km / s), and the horizontal axis represents time (ns). Curve CV represents the time course of particle velocity. As shown in FIG. 17, the curve CV has a third slope SLA and a fourth slope SLB. On the time axis, the third slope SLA is located forward of the fourth slope SLB.

As shown in FIG. 16A and FIG. 17, the particle velocity has transitioned to a third slope SLA corresponding to the first slope SL1 of the first pulse light PL1. From the transition of the particle velocity such as the third slope SLA, it can be inferred that the first shock wave SW1 has an edge EG1 as shown in FIG. 3 (b). That is, it can be estimated that the inclination of the edge EG1 of the first shock wave SW1 is gentler than the inclination of the edge EGa of the shock wave SWa generated by the comparison pulse light PLC (a symmetrical pulse light having a Gaussian distribution).

Second Embodiment
A second embodiment of the present invention will be described with reference to FIGS. 9 (b), 9 (c) and 18 (a) to 19 (d). In the second example, shock wave propagation was simulated by the laser peening method according to the third embodiment described with reference to FIGS. 9 (b) and 9 (c). In the simulation, the object 5 was an austenitic stainless steel. The diameter DM1 of the non-irradiation area W1 was 1 mm, and the diameter DM2 of the irradiation area W2 was 5 mm. The wavelength of the pulsed light PLD was 1054 nm, the energy of the pulsed light PLD was 600 J, and the time width of the pulsed light PLD was 5 ns. The target 5 did not have the specific layer LY, and was the target TA itself.

18 (a) to 18 (d) are diagrams showing shock waves according to the second embodiment in time series. FIGS. 19 (a) to 19 (d) are shockwaves according to the second embodiment, and are diagrams showing the shockwaves after the shockwaves shown in FIG. 18 (d) in time series. In each of FIGS. 18A to 19D, the vertical axis indicates the surface position (mm) of the object 5 and the horizontal axis indicates the depth (mm) from the surface 5 a of the object 5. On the vertical axis, the center C of the non-irradiation area W1 is set to "0". In each of FIGS. 18 (a) to 19 (d), a white area indicates a shock wave. Furthermore, in the upper part of each of FIGS. 18A to 19D, the elapsed time (ns) from the time of irradiation of the pulsed light PLD to the irradiation area W2 is shown.

As shown in FIG. 18 (a), when the pulsed light PLD is irradiated to the irradiation area W2, a shock wave propagating from the irradiation area W2 in the depth direction DP is generated. In particular, as shown in FIGS. 18A and 18B, the shock wave WA1 generated in the vicinity of the boundary between the non-irradiation area W1 and the irradiation area W2 is a composite vector VR1 in the direction AW1 (FIG. 11A). I'm heading for On the other hand, the shock wave WA2 generated in the vicinity of the boundary between the non-irradiation area W1 and the irradiation area W2 travels in the direction AW2 (corresponding to the composite vector VR2 in FIG. 11A). As a result, as shown in FIG. 18C, the shock wave WA1 and the shock wave WA2 interfere with each other to generate a synthetic shock wave WAS. The depth DTP at which the shock wave WA1 and the shock wave WA2 interfere was about 0.5 mm. Therefore, it has been confirmed that the depth DTP at which the shock wave WA1 and the shock wave WA2 interfere with each other is substantially equal to the radius R (= 0.5 mm) of the non-irradiation area W1.

Then, as shown in FIGS. 18 (d) and 19 (a) to 19 (d), the combined shock wave WAS propagates in the depth direction DP. The synthetic shock wave WAS attenuated so as to propagate in the depth direction DP. However, as shown in FIGS. 19 (a) to 19 (d), it was confirmed that the synthetic shock wave WAS reaches a deeper position than the shock wave around the synthetic shock wave WAS.

Third Embodiment
A third embodiment of the present invention will be described with reference to FIGS. 9 (b), 9 (c), 12 and 20. FIG. In the third example, the laser peening method shown in FIG. 9B and FIG. 9C was performed using the laser peening apparatus 100A according to the third embodiment described with reference to FIG. However, in the laser peening apparatus 100A, instead of providing the diameter setting portion 73, a steel ball with a diameter of 1 mm was installed on the surface 5a of the object 5. Then, the pulsed light PL having a substantially circular cross-sectional view is emitted toward the surface 5 a so as to include the steel ball. As a result, the area | region where the steel ball was installed among the surface 5a became non-irradiation area | region W1. Therefore, the diameter DM1 of the non-irradiated area W1 was 1 mm. On the other hand, the area surrounding the area where the steel ball was installed became the irradiation area W2. The diameter DM2 of the irradiation area W2 was 5 mm. Note that one shot of pulsed light PL was emitted.

The object 5 was stainless steel (SUS304). The target 5 did not have the specific layer LY, and was the target TA itself. The wavelength of the pulsed light PL was 1054 nm, the energy of the pulsed light PL was 623 J, and the time width of the pulsed light PL was 5 ns. The pulsed light PL had a Gaussian distribution. The intensity of the pulsed light PL (that is, the intensity of the pulsed light PLD) in the irradiation region W2 was 6.3 × 10 ¹¹ (W / cm ² ).

In the third example, residual stress was generated in the object 5 by the laser peening method shown in FIGS. 9 (b) and 9 (c). Then, the residual stress formed inside the object 5 was measured by the sin ² φ method using X-ray diffraction. Specifically, the residual stress below the center C of the non-irradiated area W1 was measured. The X-ray diffractometer was the same as the X-ray diffractometer used in the first example.

FIG. 20 is a view showing a residual stress field according to the third embodiment. In FIG. 13, the vertical axis represents residual stress (megapascals: MPa), and the horizontal axis represents depths (micrometers: mm) from the surface 5 a of the object 5.

As shown in FIG. 20, a positive value of residual stress indicates a tensile residual stress (tensile residual stress), and a negative value of residual stress indicates a compressive residual stress (compression residual stress). The compressive residual stress was present to a depth of about 3.5 mm. That is, it was confirmed that a compressive residual stress field was formed up to a depth of about 3.5 mm.

Specifically, the peak value PV of compressive residual stress was located at a depth of about 0.5 mm. On the other hand, the radius R of the non-irradiation area W1 was 0.5 mm. Therefore, it has been confirmed that the radius R of the non-irradiated area W1 is equal to the depth DTP with respect to the non-irradiated area W1 of the peak value PV of the compressive residual stress applied to the object 5 by the shock wave based on the pulsed light PL.

In addition, it can be confirmed that the compressive residual stress is attenuated while repeating attenuation and increase from the peak value PV in the depth direction DP. It can be inferred that the reason why the compressive residual stress did not decay monotonously is the effect due to the interference between the shock wave WA1 and the shock wave WA2 facing each other.

The first embodiment and the third embodiment were compared. As shown in FIG. 13, in the first example, compressive residual stress was present to a depth of about 2 mm. On the other hand, as shown in FIG. 20, in the third example, the compressive residual stress existed to a depth of about 3.5 mm. Accordingly, it was confirmed that the compressive residual stress field can be formed to a deeper position in the third embodiment than in the first embodiment. In the third embodiment, it can be inferred that the compressive residual stress field is formed by the large pressure synthetic shock wave WAS generated by the interference between the shock wave WA1 and the shock wave WA2 facing each other.

In the third embodiment, even when the object 5 does not have the specific layer LY, a compressive residual stress field can be formed to a depth on the order of millimeters.

The embodiments and examples of the present invention have been described above with reference to the drawings (FIGS. 1 to 20). However, the present invention is not limited to the above embodiment and examples, and can be implemented in various aspects without departing from the scope of the present invention (for example, (1) to (4 shown below) )). In addition, various inventions can be formed by appropriately combining the plurality of components disclosed in the above-described embodiments. For example, some components may be deleted from all the components shown in the embodiment. In order to facilitate understanding, the drawings schematically show each component as a main component, and the thickness, length, number, spacing, etc. of each component illustrated are actually considered from the convenience of drawing creation. May be different. Further, the materials, shapes, dimensions, and the like of the components shown in the above embodiment are merely examples and are not particularly limited, and various modifications can be made without substantially departing from the effects of the present invention. is there.

(1) In the first and second embodiments described with reference to FIG. 1A and FIG. 6, a plurality of first pulse lights PL1 are continuously irradiated to one first irradiation area A1, and a plurality of The second pulsed light PL2 may be applied continuously to one second irradiation area A2 (overlap). In the first pulse light PL1, the second slope SL2 may be more gently inclined than the first slope SL1. Similarly, in the second pulse light PL2, the second slope SL22 may be sloped more gently than the first slope SL12. Each of the first pulse light PL1 and the second pulse light PL2 may be symmetrical pulse light having a Gaussian distribution with respect to the peak. In the third embodiment, a plurality of pulse lights PLD may be continuously irradiated to one irradiation area W2 (overlap).

(2) In the

embodiments

1 and 2 described with reference to FIGS. 1A and 6, the object 5 itself is the target TA that forms a compressive residual stress field, and the first pulse light PL1 and The second pulsed light PL2 was directly irradiated to the object 5. However, as long as the first shock wave SW1 and the second shock wave SW2 can be propagated into the target TA, the first pulsed light PL1 and the second pulsed light PL2 are irradiated to the target TA via the specific layer LY. It is also good. Similarly, in the third embodiment, the pulsed light PLD may be irradiated to the target TA via the specific layer LY.

For example, the object 5 may have a target TA and one or more specific layers LY. The specific layer LY covers at least the surface of the target TA.

Specifically, for example, the specific layer LY is formed of a transparent material (for example, water), and delays the generation of a dilute wave. In this case, for example, the specific layer LY is disposed on the surface of the target TA by placing the target TA in water. Since the generation of the rarefied wave is delayed by the specific layer LY, the first shock wave SW1 and the second shock wave SW2 travel to a deeper position of the target TA. As a result, a thicker compressive residual stress field can be formed. For example, the specific layer LY is formed of a black material and functions as a portion that expands by ablation pressure. Therefore, in the specific layer LY, a tensile residual stress field (hereinafter, referred to as “tensile residual stress field”) is formed. That is, the specific layer LY functions as a sacrificial layer. As a result, formation of a tensile residual stress field in the target TA can be suppressed.

Specifically, the pulse irradiation unit 3 irradiates the surface of the specific layer LY with the first pulse light PL1 so as to form the first irradiation area A1 on the surface of the specific layer LY, and the surface of the specific layer LY. The second pulsed light PL2 is irradiated on the surface of the specific layer LY so as to form a second irradiation area A2.

As described with reference to FIGS. 1A to 1C, when the object 5 does not have the specific layer LY, that is, when the specific layer LY is not disposed on the target TA. For example, the operation of placing the target TA in water and the operation of forming the specific layer LY on the surface of the target TA can be omitted. As a result, the cost at the time of forming a compressive residual stress field can be suppressed.

(3) In the second embodiment described with reference to FIGS. 6 and 7, the harmonic generation unit 21 generates the second harmonic. However, the harmonic generation unit 21 may generate second to Qth harmonics. "Q" is an integer of 3 or more.

(4) In the first embodiment described with reference to FIG. 1A, the pulse generation unit 1 generates the first pulse light PL1 and the second laser generates the second pulse light PL2. And an oscillator. In the first embodiment, as long as the intensity K1 of the first pulse light PL1 and the intensity K2 of the second pulse light PL2 are different, the wavelength λ1 of the first pulse light PL1 and the wavelength λ2 of the second pulse light PL2 are It may be identical. Alternatively, the wavelength λ1 of the first pulse light PL1 may be shorter or longer than the wavelength λ2 of the second pulse light PL2.

The present invention provides a laser peening method, a modified product production method, a laser peening apparatus, and a metal material, and has industrial applicability.

100, 100A

laser peening apparatus

1, 1A

pulse generation unit

3, 3A pulse irradiation unit 5 object 51 modified substance 51A metal material A1 first irradiation area A2 second irradiation area W1 non-irradiation area W2 irradiation area

Claims

Generating pulsed light;
Irradiating the surface of the object with the pulsed light so as to form an irradiated area surrounding a non-irradiated area of the surface of the object.
The peak value of the compressive residual stress applied to the object based on the pulsed light is positioned deeper with respect to the non-irradiated area as the diameter of the non-irradiated area is larger. Laser peening method.
The step of generating the pulsed light comprises:
Adjusting the diameter of the non-irradiated area to control the position in the depth direction of the peak value of the compressive residual stress;
The laser peening method according to claim 2, wherein the depth direction indicates a direction in which the depth increases relative to the non-irradiation area.
The radius of the non-irradiated area is substantially equal to the depth relative to the non-irradiated area of the peak value of the compressive residual stress applied to the object by the shock wave based on the pulsed light. The laser peening method of any one term.
Generating a first pulse light and a second pulse light;
The first pulse light is irradiated to the surface of the object so as to form a first irradiation region on the surface of the object, and the second irradiation region is formed on the surface of the object. Irradiating pulsed light onto the surface of the object;
The second irradiation area surrounds the first irradiation area,
The intensity of the first pulse light in the first irradiation area is different from the intensity of the second pulse light in the second irradiation area,
The intensity of the first pulse light indicates the energy of the first pulse light per unit time and per unit area;
The intensity of the said 2nd pulsed light shows the energy of the said 2nd pulsed light per unit time and per unit area, The laser peening method.
The laser peening method according to claim 5, wherein the intensity of the first pulse light in the first irradiation area is smaller than the intensity of the second pulse light in the second irradiation area.
The laser peening method according to claim 5, wherein the intensity of the first pulse light in the first irradiation area is larger than the intensity of the second pulse light in the second irradiation area.
The peak value of the compressive residual stress applied to the object based on the first pulse light and the second pulse light is deeper with respect to the first irradiation area as the diameter of the first irradiation area is larger. The laser peening method according to any one of claims 5 to 7, which is located in
The step of generating the first pulse light and the second pulse light includes
Adjusting the diameter of the first irradiation area to control the position in the depth direction of the peak value of the compressive residual stress;
The laser peening method according to claim 8, wherein the depth direction indicates a direction in which the depth becomes larger than the first irradiation region.
A method for producing a reformate, wherein the target is reformed by the laser peening method according to any one of claims 1 to 9 to produce a reformate.
A pulse generation unit that generates pulsed light;
A pulse irradiation unit that irradiates the surface of the object with the pulse light so as to form an irradiation area surrounding a non-irradiation area of the surface of the object.
A pulse generation unit that generates a first pulse light and a second pulse light;
The first pulse light is irradiated to the surface of the object so as to form a first irradiation region on the surface of the object, and the second irradiation region is formed on the surface of the object. And a pulse irradiation unit for irradiating pulse light onto the surface of the object;
The second irradiation area surrounds the first irradiation area,
The intensity of the first pulse light in the first irradiation area is different from the intensity of the second pulse light in the second irradiation area,
The intensity of the first pulse light indicates the energy of the first pulse light per unit time and per unit area;
The intensity of the said 2nd pulsed light shows the energy of the said 2nd pulsed light per unit time and per unit area, The laser peening apparatus.
Comprising a body having a surface and a portion;
The portion is located at a position distant from the surface in the depth direction,
In said part, compressive residual stress has a peak value,
The metallic material in which the compressive residual stress is attenuated while being repeatedly reduced and increased from the portion toward the depth direction.
The surface has an irradiation area of pulse light and a non-irradiation area of the pulse light,
The non-irradiated area is surrounded by the irradiated area,
The metal material according to claim 13, wherein the depth of the portion relative to the non-irradiated area is substantially equal to the radius of the non-irradiated area.