JP2014058720A - Manufacturing method for sliding member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a sliding member for improving wear resistance and for lowering friction by irradiating laser pulses to the surface of amorphous carbon film.SOLUTION: In a manufacturing method for a sliding member, in which pulse laser is irradiated to amorphous carbon film covering a sliding surface for modifying the amorphous carbon film, the pulse laser is irradiated, of which output power is controlled such that the surface of the amorphous carbon irradiated by the pulse laser does not have surface having periodicity, and the concentration of carbon gradually decreases with distance from the inside of to the surface of the amorphous carbon film.

Description

  The present invention relates to a method for manufacturing a sliding member suitable for use on a sliding surface of a mechanical part such as a bearing or a piston.

  Conventionally, sliding members have been used in various devices such as engines and transmissions in automobiles. The sliding resistance of these sliding members is reduced to reduce energy loss, and the future for protecting the global environment. Various research and development are underway to meet fuel efficiency regulations. For example, as one of such research and development, there is a technique for coating the sliding surface in order to improve the wear resistance of the sliding member and obtain low friction characteristics. Amorphous carbon coatings are attracting attention.

  The amorphous carbon film has a structure in which the carbon structure of diamond and the carbon structure of graphite are mixed, and has an abrasion resistance like diamond and a solid lubricity like graphite.

  For example, a method of manufacturing a sliding member that irradiates a pulsed laser to an amorphous carbon coating formed on a sliding surface is proposed so that the hardness decreases as it goes from the inside of the amorphous carbon coating to the sliding surface. (See, for example, cited document 1).

JP2011-168845A

  However, as disclosed in Patent Document 1, by irradiating the surface of the amorphous carbon coating with a pulse laser, the surface layer of the amorphous carbon coating is modified and graphitized. According to the experiment described later, when the pulse laser is irradiated by the method shown in Patent Document 1, a part of the carbon of the amorphous carbon coating is removed, and the sliding surface of the amorphous carbon coating is periodic. It may become a surface with the property. As a result, since the surface having periodicity is graphitized as described above, the surface is easily worn, and the friction coefficient tends to increase as the sliding time elapses.

  The present invention has been made in view of these points, and the object is to irradiate the surface of the amorphous carbon coating with a pulsed laser to reduce friction while improving wear resistance. An object of the present invention is to provide a method of manufacturing a sliding member that can be achieved.

  In view of the above problems, a manufacturing method of a sliding member according to the present invention is a sliding member that modifies the amorphous carbon coating by irradiating the amorphous carbon coating coated on the sliding surface with a pulse laser. The surface of the amorphous carbon coating does not become a periodic surface, and the carbon density is gradually lowered as it advances from the inside of the amorphous carbon coating to the surface. The pulsed laser adjusted to such an output is irradiated on the surface of the amorphous carbon film.

  According to the present invention, when the amorphous carbon coating is irradiated with the pulse laser, the sliding surface is graphitized to have a lower density than the amorphous carbon coating inside, so that the sliding member The friction coefficient can be reduced. Furthermore, since the sliding surface of the sliding member does not have periodicity, wear resistance can be improved as compared with that having periodicity.

Furthermore, as a preferable aspect, a femtosecond laser is used as the pulse laser, and irradiation is performed with a fluence of 0.04 J / cm ^{2 to} 0.09 J / cm ² . By irradiating a pulsed laser with a fluence in such a range, the surface of the amorphous carbon film does not become a periodic surface, and as it advances from the inside of the amorphous carbon film to the surface It is possible to easily manufacture a sliding member whose carbon density is gradually lowered.

That is, when the fluence is less than 0.04 J / cm ² , graphitization of the sliding surface (carbon density reduction) is not sufficiently promoted, and low friction of the sliding member cannot be expected. If it exceeds 0.09 J / cm ² , the sliding surface becomes a periodic sliding surface, and the wear of the amorphous carbon coating is easily promoted.

Here, the "pulsed laser" is output light intensity is that of the laser oscillating by a predetermined duration changes with time, in the present specification, in particular a pulse width of 10 ^-9 seconds to 10 ^{- The 15} lasers are called pulse lasers. “Fluence” is the energy density (J / cm ² ) obtained by dividing the output energy per pulse of the laser by the irradiation cross section. Generally, if a laser beam is irradiated in a low fluence range near the minimum value of energy density (ablation threshold) where the material surface evaporates when the laser beam is irradiated on the material surface, thermal effects may hardly occur. Are known.

  According to the present invention, by irradiating the surface of the amorphous carbon film with a pulse laser, it is possible to reduce friction while improving wear resistance.

It is a schematic block diagram regarding the manufacturing apparatus for enforcing the manufacturing method of the sliding member of this invention. It is explanatory drawing which shows the irradiation operation | movement of the pulse laser with respect to a flat sliding member surface. FIG. 3A is a photograph showing the surface of the sliding member irradiated with a pulsed laser at a fluence of 0.06 J / cm ² in Example 2 under a microscope, and FIG. A photograph when the surface of a sliding member irradiated with a pulse laser at 0.08 J / cm ² is observed with a microscope, (c) is a slide irradiated with a pulse laser at a fluence of 0.16 J / cm ² in Comparative Example 4 The photograph figure when the surface of a member is observed with a microscope. The figure which showed the result of the friction and abrasion test of the sliding member which concerns on Examples 1-3 and Comparative Examples 1-3. The figure for demonstrating the principle of a density measurement test.

  Hereinafter, embodiments according to the present invention will be described in detail.

  First, a base material for the sliding member is prepared. The base material of the sliding member is not particularly limited as long as it is a material and surface hardness that can ensure adhesion to the amorphous carbon coating during sliding, such as metal, ceramic, or resin. The material of the other sliding member that slides with this sliding member is not particularly limited as long as the surface hardness is extremely low with respect to the amorphous carbon coating and is not easily worn when sliding. Is not to be done.

  Next, a physical vapor deposition method such as a plasma PVD method, a sputtering method, a vacuum deposition method, a non-equilibrium magnetron sputtering method, or plasma CVD so that an amorphous carbon film is coated on the sliding surface of the sliding member. An amorphous carbon film is formed by using a chemical vapor deposition method such as a method or an arc ion plating method. As long as the amorphous carbon film can be formed on the sliding surface of the sliding member, the film forming method is not particularly limited.

  In addition, the amorphous carbon film may contain additional elements such as Si, Ti, Cr, Fe, W, and B, and the surface hardness of the film is adjusted by adding such elements. You can also

  The film thickness of the amorphous carbon film formed on the sliding surface of the sliding member is preferably 3 μm to 30 μm. If the thickness is less than 3 μm, the amorphous carbon film may be removed due to wear, and if the thickness is more than 30 μm, the amorphous carbon film is easily affected by internal compressive stress.

  Next, the amorphous carbon coating coated on the sliding surface is irradiated with a pulse laser. Specifically, pulse laser irradiation is performed using the manufacturing apparatus shown in FIG. The manufacturing apparatus includes at least a pulse laser system 1, a shutter 2, a laser control unit 3, reflecting mirrors 4 and 5, a concave reflecting mirror 6, and a three-axis stage 7. In addition to condensing by the concave reflecting mirror 6, the laser may be condensed using a lens made of quartz or the like.

As the pulse laser system 1, a known pulse laser system that oscillates a femtosecond laser is used. A pulse laser other than a femtosecond laser can also be used. In other words, a modified layer can be formed if high density energy can be applied locally within a range where the amorphous carbon film does not change due to thermal and mechanical influences. Depending on the state of the coating (layer thickness, external environment such as base material), for example, picosecond (10 ⁻⁹ to 10 ⁻¹² seconds) laser or nanosecond (10 ⁻⁶ to 10 ⁻⁹ seconds) laser A pulse laser system that oscillates a pulse laser may be used.

  The laser pulse oscillated from the femtosecond laser system 1 passes through the shutter 2 and enters the laser control unit 3. The laser control unit 3 converts the wavelength of the laser pulse and performs polarization control. In the polarization control, linearly polarized light (longitudinal / lateral direction) and circularly polarized light are performed as necessary. When linearly polarized light is used, a fine structure in which elongated grooves are periodically formed is formed. When circularly polarized light is formed, a fine structure in which granular protrusions are periodically formed is obtained.

  The laser pulse emitted from the laser control unit 3 is reflected by the reflecting mirrors 4 and 5, enters the concave reflecting mirror (parabolic mirror) 6, and is condensed. Then, the condensed laser pulse is irradiated on the surface (sliding surface) of the amorphous carbon film of the sliding member M installed on the sample stage of the triaxial stage 7.

  The 3-axis stage 7 includes a Z-axis stage to which a sample stage is attached and an XY-axis stage to which the Z-axis stage is attached. The XY-axis stage and the Z-axis stage are moved based on a control signal from the control device 8. The irradiation position of the surface (sliding surface) of the amorphous carbon coating of the sliding member M is moved.

  In this embodiment, the sliding member M is moved to irradiate the laser pulse. However, the laser pulse oscillation and the apparatus side including the optical system may be moved, or both may be moved. The irradiation position on the surface of the sliding member M may be positioned.

  FIG. 2 is an explanatory view showing the pulse laser irradiation operation on the surface of the flat sliding member M. FIG. In this example, the main scanning direction is taken as the Z axis, and the sub scanning direction is taken as the X axis. The irradiation position is shown by one circle, and the inside of the circle is the irradiation area. When irradiating in the main scanning direction, the Z-axis stage is moved at a predetermined speed in the Z-axis direction. At this time, the surface of the sliding member M is irradiated in a band shape while the irradiation spots overlap in the main scanning direction Z1 (specifically, the overlapping circles overlap with each other so that the center of the adjacent circle coincides with a part of the circumference). To.

  After irradiation in the main scanning direction Z1, the sliding member M is shifted in the X-axis direction by the XY-axis stage. At that time, positioning is performed in the sub-scanning direction so as to overlap the irradiation region in the main scanning direction Z1. In this example, the irradiation area is shifted in the sub-scanning direction by the radius of the circle indicating the irradiation area. Therefore, the next irradiation area in the main scanning direction Z2 and the irradiation area in the main scanning direction Z1 are positioned so as to overlap each other. Then, the irradiation operation is performed while moving the irradiation position at a predetermined speed in the main scanning direction Z2 as in the main scanning direction Z1. Thereafter, the irradiation operation is repeated in the main scanning direction while shifting in the sub-scanning direction, so that the irradiation operation is performed a plurality of times uniformly on the surface of the substrate T.

  Since there is a difference in irradiation energy between the central portion and the peripheral portion of the irradiation spot of the laser pulse, the overlapping portion of the irradiation spots is adjusted as appropriate so that the irradiation energy of the entire irradiation region is substantially uniform. At this time, the surface of the amorphous carbon film does not become a periodic surface by a pulse laser (so that part of the amorphous carbon film is not removed by the pulse laser), and the amorphous carbon film The surface of the amorphous carbon coating is irradiated with a pulsed laser adjusted to an output in which the carbon density decreases in a gradient as it goes from the inside of the coating to the surface.

More specifically, in this embodiment, unlike the conventionally known pulse laser irradiation, a femtosecond laser is used as the pulse laser, and irradiation is performed with a fluence of 0.04 J / cm ^{2 to} 0.09 J / cm ^2. . That is, according to experiments by the inventors, when a known pulse laser system that oscillates a femtosecond laser is used, a part of the amorphous carbon film is pulsed by irradiating the pulse laser in such a range. Since it is not removed by the laser, the surface of the amorphous carbon film does not become a periodic surface, and the carbon density decreases gradually as it moves from the inside of the amorphous carbon film to the surface. It was. That is, when the fluence is less than 0.04 J / cm ² , graphitization of the sliding surface (carbon density reduction) is not sufficiently promoted, and low friction of the sliding member cannot be expected. When 0.09 J / cm ² is exceeded, a part of the amorphous carbon film is removed by the pulse laser, and the sliding surface becomes a periodic sliding surface. Is easily promoted.

The following invention will be described based on examples.
[Examples 1 to 4]
The sliding member which concerns on Examples 1-4 was manufactured as shown below. The surface of the base material made of a flat (50 × 50 × 10 mm) silicon block was coated with an amorphous carbon film with a thickness of 82 nm on the sliding surface of the sliding member by a known plasma CVD apparatus. In this embodiment, the amorphous carbon film having such a film thickness is formed. The same applies to the amorphous carbon films of Comparative Examples 1 to 4 shown below.

Using a sliding member on which an amorphous carbon film was formed, surface processing was performed by irradiating linearly polarized laser pulses with the manufacturing apparatus shown in FIG. As a femtosecond laser system, IBRIT made by Cyber Laser Co., Ltd. is used, and a laser pulse with a wavelength of 800 nm, a pulse width of 180 fs, a pulse energy maximum of 1.0 mJ, and a frequency of 1.0 kHz is linearly polarized, The light was collected and irradiated perpendicularly to the surface of the amorphous carbon film of the sliding member in the atmosphere with a laser output of 150 mW to 410 mW. The spot area of the laser pulse was 2.497 μm ² . To set the fluence of the laser pulse to 0.04J ^/ cm ² ~0.09J ^/ cm 2 in the vicinity of the ablation threshold (specifically, in the order of Examples ^{1~4, 0.04J / cm 2, 0.06J} / ^{cm 2, 0.08J / cm 2,} 0.09J / cm 2), the stage moving speed while irradiating the laser pulse was adjusted irradiating operation by adjusting the 8 mm / s at 1000 pulses per second. The shift amount in the sub-scanning direction was set to 60 μm. Each fluence of the laser pulse was adjusted by changing the laser output.

[Comparative Examples 1-4]
A sliding member was produced in the same manner as in Example 1. The difference from Example 1 is that Comparative Example 1 is a sliding member in which the surface of the amorphous carbon film is not irradiated with a pulse laser, and Comparative Examples 2 to 4 use femtosecond lasers as pulse lasers in order. ^{0.02J / cm 2, 0.10J / cm} 2, in that to produce a sliding member was irradiated with fluence 0.16J / cm ^2.

<Surface observation>
The surfaces of the amorphous carbon coatings of the sliding members according to Examples 2 and 3 and Comparative Example 4 were observed with a microscope. FIG. 3A is a photograph showing the surface of the sliding member irradiated with a pulsed laser at a fluence of 0.06 J / cm ² in Example 2 under a microscope, and FIG. A photograph when the surface of a sliding member irradiated with a pulse laser at 0.08 J / cm ² is observed with a microscope, (c) is a slide irradiated with a pulse laser at a fluence of 0.16 J / cm ² in Comparative Example 4 It is a photograph figure when the surface of a member is observed with a microscope.

[Result 1]
In all of the sliding members according to Examples 2 and 3, the surface (sliding surface) of the amorphous carbon coating was not a surface having periodicity. On the other hand, when a femtosecond laser is used as the pulse laser and the fluence is 0.16 J / cm ² (Comparative Example 4), the surface (sliding surface) of the amorphous carbon film has a periodic structure, and the periodic structure is polarized light. It was formed in a direction perpendicular to the direction E.

<Friction and wear test>
A sliding test of the amorphous carbon coating was performed using a ring-on-plate test apparatus. It used as a plate test piece of the sliding member (diameter 45mm) which concerns on Examples 1-3 and Comparative Examples 1-4. A ring test piece made of material FC230 having an outer diameter of 25.6 mm, an inner diameter of 20 mm, and a height of 18 mm was manufactured. A paraffinic system having a viscosity of 14.8 mm ² / s, in which the sliding surface of the plate test piece (the surface coated with the amorphous carbon coating) and the end face of the ring test piece were brought into contact with each other and heated to 60 ° C. ± 1. While supplying mineral oil (without additives) as a lubricating oil, a friction / wear test was conducted at a peripheral speed of 2 m / sec, a surface pressure of 4.4 MPa, and a sliding distance of 10.000 mm, and a friction coefficient was measured. The result is shown in FIG. FIG. 3 also shows the result of the friction coefficient.

[Result 2]
The friction coefficient of the sliding member according to Examples 1 to 3 is the friction of the sliding member according to Comparative Examples 1 and ² (fluency 0 J / cm ² (not irradiated with laser pulse), 0.02 J / cm ² ). The result was lower than the coefficient. From this result, it is considered that when the fluence was 0.04 J / cm ² or less, the surface modification (graphitization) of the amorphous carbon coating was not sufficient. Further, although the friction coefficient of the sliding member according to Comparative Example 3 (Fluence 0.10 J / cm ² ) was low, the amount of wear was larger than that of the sliding member according to Example 1 when the sliding surface was observed. . Further, when the sliding surface of the sliding member according to Comparative Example 4 (Fluence 0.16 J / cm ² ) was observed, the amount of wear was larger than that of the sliding member according to Example 1, and the friction coefficient was also increased. As a result, since the surface of the sliding member according to Comparative Example 3 (when irradiated with a pulse laser exceeding fluence 0.09 J / cm ² ) is a sliding surface having a periodic structure, It is considered that the wear of the crystalline carbon film is easily promoted.

As a result, by using a femtosecond laser as a pulse laser and irradiating with a fluence of 0.04 J / cm ^{2 to} 0.09 J / cm ² , the surface of the amorphous carbon film has a periodicity. In addition, the carbon density is gradually lowered as it advances from the inside of the amorphous carbon coating to the surface, and a sliding member that can achieve low friction while improving wear resistance can be obtained. Conceivable.

<Density measurement test>
For the sliding member according to Example 2 (Fluence 0.06 J / cm ² ) and the sliding member according to Comparative Example 1 (without laser pulse irradiation), the number of carbon atoms was determined by neutron reflection method. Density was measured. Specifically, under the conditions shown in FIG. 5 and Table 1, the beam of the neutron beam source is made to slide on the sliding surface of the sliding member (the amorphous carbon film is formed through the slits 1 and 2 that are spaced apart. The scattering length density Nb was determined from the obtained scattering vector. The scattering length density Nb is a value proportional to the atomic number density N (number / cm ³ ), and is given by the product of N and the nuclear scattering amplitude b (cm). Since the nuclear scattering amplitude b is an element-specific value (known), the atomic number density can be calculated when Nb is obtained from the analysis. The results are shown in Table 2.

[Result 3]
As shown in Table 2, when the pulse laser is irradiated as in the sliding member of Example 2, the carbon density is gradually lowered as it advances from the inside of the amorphous carbon coating to the surface. It could be confirmed. Furthermore, it was found that the film thickness (volume) of the amorphous carbon film according to Example 2 was increased by irradiating a pulse laser. From these results, it is considered that the amorphous carbon film coated on the sliding surface was irradiated with a pulsed laser, whereby the graphitization of the amorphous carbon material was promoted as the sliding surface was approached.

<Raman measurement test>
The sliding member according to Example 2 (Fluence 0.06 J / cm ² ), the sliding member according to Example 3 (Fluence 0.08 J / cm ² ), and the sliding member according to Comparative Example 4 (Fluence 0. 16 J / cm ² ), the Raman intensity ratio was measured using a Raman spectroscopic measurement device (manufactured by Nihon Electronics Co., Ltd., LABRAM, laser spot diameter 2 μm). For these sliding members, the intensity ratio (ID / IG) of Raman scattering peak intensity (hereinafter referred to as “Raman intensity”) is also applied before the pulse laser irradiation and after the above-described friction / wear test (sliding test). Ratio ").

[Result 4]
As shown in Table 3, in any case, the Raman intensity ratio increased after irradiation with the pulse laser, and the surface layer of the amorphous carbon film was graphitized by irradiation with the pulse laser. I understand. In the Raman spectroscopic measurement, the intensity ratio of the Raman scattering peak intensity (ID) appearing at 1355 cm ⁻¹ based on the sp ² bond and the Raman scattering peak intensity (IG) appearing at 1590 cm ⁻¹ based on the sp ³ bond (ID / IG) before and after the irradiation treatment and after the sliding test, Examples 2 and 3 have no change (no wear), whereas Comparative Example 4 has a structure that changes after sliding (friction). It is easy to understand.

M Sliding member 1 Pulse laser system 2 Shutter 3 Laser control unit 4 Reflecting mirror 5 Reflecting mirror 6 Concave reflecting mirror 7 Triaxial stage 8 Controller

Claims (2)

A method for producing a sliding member for modifying an amorphous carbon coating by irradiating an amorphous carbon coating coated on a sliding surface with a pulse laser,
The pulse adjusted to an output in which the surface of the amorphous carbon coating does not become a periodic surface and the carbon density is gradually lowered as it advances from the inside of the amorphous carbon coating to the surface. A method for producing a sliding member, wherein the surface of the amorphous carbon coating is irradiated with a laser. The method for manufacturing a sliding member according to claim 1, wherein a femtosecond laser is used as the pulse laser, and irradiation is performed with a fluence of 0.04 J / cm ^{2 to} 0.09 J / cm ² .

Images