JP2018069328A - Friction stir welding tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a friction stir welding tool having long life.SOLUTION: A friction stir welding tool includes base material and a coating film for covering a surface of the base material. The coating film includes a compound layer consisting of a composition of TiMCN(where M is one or more elements (however, Ti is excluded) selected from a group consisting of a 4-group element, a 5-group element, a 6-group element in a periodic table, Al, Si, and B, and x and y satisfy 0.2≤x≤1, and 0≤y≤1), and the compound layer has an elastic recovery rate of 52% or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a friction stir welding tool.

  In the United Kingdom in 1991, a friction stir welding technique for joining metal materials (materials to be joined) such as aluminum alloys was established. This technology generates frictional heat by rotating while pressing a cylindrical friction stir welding tool having a small-diameter protrusion formed at the tip on the joining surface between metal materials intended for joining, This is a technique of joining metal materials by softening and plastically flowing the metal material of the joint portion by the frictional heat.

  The “joining portion” refers to a joining interface portion where joining of metal materials is desired by abutting metal materials or placing metal materials in an overlapping manner. In the vicinity of the bonding interface, the metal material is softened to cause plastic flow. When the metal material is stirred, the bonding interface disappears and bonding is performed. Furthermore, since dynamic recrystallization occurs simultaneously in the metal material, the metal material in the vicinity of the bonding interface is atomized by the dynamic recrystallization, and the metal materials can be bonded with high strength.

  With regard to such a friction stir welding tool, a technique has been developed in which a coating is provided on the surface of a base material to improve tool characteristics. For example, Japanese Unexamined Patent Application Publication No. 2013-000773 (Patent Document 1) discloses a friction stir welding tool in which a coating having a characteristic heat permeability and a characteristic crystal structure is provided on the surface of a base material. ing. According to this friction stir welding tool, in addition to wear resistance, peeling resistance and chipping resistance are improved.

JP2013-000773A

  By the way, at the time of joining of the workpieces, a portion of the friction stir welding tool in contact with the workpiece is exposed to a high temperature and a large load that is twisted in the rotational direction is applied. For this reason, in the conventional friction stir welding tool, there are cases where defects such as defects and / or cracks occur at the contact portion, and as a result, there is a problem that a sufficiently long life cannot be exhibited.

  It is an object of the present disclosure to provide a friction stir welding tool having a long life.

A friction stir welding tool according to one embodiment of the present disclosure is a friction stir welding tool including a base material and a coating that covers a surface of the base material, and the coating is Ti _x M _{1-x Cy} N _1-y (M is one or more elements selected from the group consisting of group 4 elements, group 5 elements, group 6 elements, Al, Si and B in the periodic table (excluding Ti), 0.2 ≦ x ≦ 1 and 0 ≦ y ≦ 1), and the compound layer has an elastic recovery rate of 52% or more.

  According to the above, a friction stir welding tool having a long life can be provided.

FIG. 1 is a cross-sectional view illustrating an example of a friction stir welding tool according to an embodiment.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described. In the present specification, the notation in the form of “A to B” means the upper and lower limits of the range (that is, A or more and B or less), and there is no unit description in A, and the unit is described only in B The unit of A and the unit of B are the same.

[1] A friction stir welding tool according to an aspect of the present disclosure is a friction stir welding tool including a base material and a coating that covers a surface of the base material, and the coating is Ti _x M _1-x C _y N _1-y (M is one or more elements selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, Al, Si and B in the periodic table (excluding Ti), 0.2 ≦ x ≦ 1 and 0 ≦ y ≦ 1), and the compound layer has an elastic recovery rate of 52% or more.

  At the time of joining using the friction stir welding tool, a large load (stress) is applied to the contact portion with the material to be joined, thereby causing deformation of the contact portion. When the friction stir welding tool is provided with a coating, the contact portion is composed of a substrate and a coating that covers the surface of the substrate. Usually, the substrate tends to have better toughness than the coating, and the coating tends to have better hardness than the substrate. For this reason, in the conventional friction stir welding tool, the coating cannot follow the deformation of the base material, and the coating is plastically deformed. It was.

  On the other hand, according to the friction stir welding tool, the coating film has a compound layer having the characteristic composition and having an elastic recovery rate of 52% or more. Such a compound layer can have high toughness in addition to high hardness, high heat resistance, and chemical stability. For this reason, the film which has the said compound layer can fully follow the deformation | transformation of a base material. Therefore, according to the tool for friction stir welding, the occurrence of coating defects and cracks as in the conventional case is suppressed, and thus a long life can be obtained.

  [2] In the friction stir welding tool, M includes at least one of Si and B. This further improves the elastic recovery rate of the compound layer.

  [3] In the friction stir welding tool, the compound layer does not include a hexagonal crystal structure. When the compound layer includes a hexagonal crystal structure, the hardness of the compound layer tends to decrease. In other words, a compound layer that does not include a hexagonal crystal structure can have high hardness.

  [4] In the friction stir welding tool, the compound layer has a thickness of 2 μm to 16 μm. Thereby, the said effect can be exhibited suitably, fully suppressing peeling of a compound layer.

  [5] In the friction stir welding tool, the coating includes an intermediate layer between the substrate and the compound layer, and the intermediate layer has a thickness of 4 μm or less. Thereby, both the characteristics of the compound layer and the characteristics of the intermediate layer can be exhibited synergistically.

[6] In the friction stir welding tool, the base material has a Vickers hardness of 16 GPa or more and a fracture toughness value of 7.0 MPa · m ^1/2 or less. When the friction stir welding tool includes such a base material, the characteristics of the coating are remarkably reflected.

[Details of the embodiment of the present invention]
Hereinafter, an embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described. However, this embodiment is not limited to these. In the drawings used for describing the following embodiments, the same reference numerals represent the same or corresponding parts. Further, in the present specification, when a compound or the like is represented by a chemical formula, when the atomic ratio is not particularly limited, it includes any conventionally known atomic ratio, and is not necessarily limited to a stoichiometric range. For example, when “TiCN” is described, the ratio of the number of atoms constituting TiCN is not limited to Ti: C: N = 1: 0.5: 0.5, and any conventionally known atomic ratio is included.

<Friction stir welding tool>
The friction stir welding tool of this embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view illustrating an example of a friction stir welding tool according to an embodiment. The friction stir welding tool 1 of the present disclosure (hereinafter also referred to as “tool 1”) includes a base material 2 and a coating 3 that covers the surface of the base material 2.

  The base material 2 has a shape including a probe portion 4 having a small diameter (for example, a diameter of 2 to 8 mm) and a cylindrical portion 5 having a large diameter (for example, a diameter of 4 to 20 mm). A chuck portion 7 is provided for being chucked by the holder. Such a chuck portion 7 can be formed, for example, by cutting a part of the side surface of the cylindrical portion 5. Further, the portion that expands from the probe portion 4 (the portion that contacts the material to be joined at the time of joining processing) is also referred to as a shoulder portion 6.

  The tool 1 having such a configuration can be used extremely usefully for, for example, a point joining (FSJ) application, a line joining (FSR) application, and the like.

  Specifically, in the FSJ application, the probe unit 4 is pressed or inserted into a portion to be joined in two materials to be joined that are stacked or abutted vertically, and the tool 1 is rotated in that state. Then, while pressing the rotating probe portion 4, the probe portion 4 is continuously rotated at that location, thereby joining the materials to be joined together. On the other hand, in the FSW application, the probe unit 4 is pressed or inserted into the joining target portion of the two materials to be joined that are stacked or butted together vertically, and the tool 1 is rotated in that state. And the to-be-joined materials are joined by moving the rotating probe part 4 linearly with respect to the said laminated | stacked or faced part.

  Although FIG. 1 shows the case where the chuck portion 7 is provided on the base material 2, the chuck portion 7 may not be provided. Moreover, in FIG. 1, although the film 3 is provided only in the surface of the contact part (the probe part 4 and the shoulder part 6) of the base materials 2, the structure of the film 3 is not restricted to this. For example, it may be provided on the entire surface of the substrate 2, or may be provided on the entire surface except for the chuck portion 7.

  However, from the viewpoint of preventing the base material 2 from becoming high temperature, the coating is applied only on the surface of the contact portion (probe portion 4 and shoulder portion 6) of the base material 2 or on the entire surface except the chuck portion 7. Is preferably provided, and more preferably provided only on the surface of the contact portion (probe portion 4 and shoulder portion 6) of the substrate 2. Since heat generated by friction is easily released from the portion where the coating 3 is not provided to the holder, the base material 2 is unlikely to become high temperature, and thus deformation of the base material 2 can be suppressed, and This is because a decrease in wear resistance of No. 2 can be suppressed.

"Base material"
The base material 2 can use a conventionally well-known thing as a base material of the tool for friction stir welding without limitation. For example, cemented carbide (for example, WC base cemented carbide, including WC, including Co, or further including carbonitride such as Ti, Ta, Nb, etc.), cermet (TiC, TiN, TiCN, etc.) High-speed steel, tool steel, ceramics (such as titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, sialon, and mixtures thereof), cubic boron nitride sintered body And diamond sintered bodies, hard materials in which cubic boron nitride particles are dispersed, and the like.

In particular, when the tool 1 includes the base material 2 having a Vickers hardness of 16 GPa or more and a fracture toughness value of 7.0 MPa · m ^1/2 or less, the characteristics of the coating 3 are significantly reflected in the characteristics of the tool 1. As a result, the tool 1 can have a significantly long service life. The base material 2 more preferably has a Vickers hardness of 16 to 25 GPa and a fracture toughness value of 4.0 to 7.0 MPa · m ^1/2 .

The Vickers hardness of the base material 2 is measured according to JIS R1610: 2003. Moreover, the fracture toughness value of the base material 2 is measured in accordance with JIS R1607: 2010. Specifically, first, the surface of the substrate 2 is exposed, and the surface is further mirror-polished using diamond abrasive grains. Next, a Vickers hardness test is performed on the mirror surface of the substrate 2 using a diamond indenter. Thereby, Vickers hardness (GPa) is measured. In addition, by using an indentation-fracture method (IF method), the fracture toughness (MPa · m ¹ ) can be determined from the size of the indenter mark and the crack length in the substrate 2 after the Vickers hardness hardness test. ^{/ 2} ) is required.

  An example of the base material 2 that satisfies the above Vickers hardness and fracture toughness values is cemented carbide. A particularly preferable cemented carbide may be a cemented carbide containing WC particles and a binder. The content ratio of the WC particles in the cemented carbide is preferably 87 to 95% by mass, preferably includes Co as a binder, and more preferably includes Cr. This is because such a cemented carbide has an excellent balance of both hardness and toughness. The average particle size of the WC particles is not particularly limited, and can be set to 0.2 to 2.0 μm, for example. In addition, the cemented carbide may contain an abnormal phase called free carbon or η phase in the structure as long as the effect of the present invention is exhibited.

<Coating>
The coating 3 only needs to cover at least the probe portion 4 and the shoulder portion 6 of the substrate 2 as described above.

  The thickness in particular of the film 3 is not restrict | limited, For example, it can be set to 2-22 micrometers. When the thickness of the coating 3 is less than 2 μm, the thickness of the compound layer described later becomes insufficient, and the desired effect tends not to be sufficiently exhibited. When the thickness of the coating 3 exceeds 22 μm, the coating 3 itself may be destroyed.

  The thickness of the coating 3 can be determined as follows. First, as described above, an arbitrary position of the tool 1 is cut to prepare a sample including a cross section of the coating 3. The produced cross section is observed with an SEM, and the magnification is adjusted so that the entire area of the coating 3 in the thickness direction is included in the observed image. Then, the thickness is measured at five or more points, and the average value is defined as the thickness of the coating 3. The thickness of each layer described in detail below can also be measured by the same method.

As long as the film 3 includes the following compound layers, the film 3 may include other layers. Examples of the other layers include an intermediate layer provided between the substrate 2 and the compound layer, and a surface layer constituting the outermost surface of the coating 3.
<Compound layer>
The compound layer included in the coating 3 satisfies the following (1) and (2).
(1) Ti _x M _{1-x Cy} N _1-y (M is one or more elements selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, Al, Si and B in the periodic table) (Excluding Ti) and satisfying 0.2 ≦ x ≦ 1 and 0 ≦ y ≦ 1);
(2) It has an elastic recovery rate of 52% or more.

  Regarding (1) above, for example, when M is two elements, the total atomic ratio of the two elements is (1-x).

Regarding (2) above, the elastic recovery rate is determined by the nanoindentation method. Specifically, first, polishing is performed so that a surface (inclined surface) having an inclination of 6 ° with respect to the surface direction of the outermost surface of the coating 3 is obtained at the position where the coating 3 of the tool 1 is provided. A nanoindentation method is applied to the surface of the compound layer included in the obtained inclined surface by applying a controlled indentation load so that the indentation depth (h) is 1/10 or less of the film thickness of the compound layer. Perform measurement by And the maximum indentation depth (hmax) in the said test and the indentation depth (hp) after load unloading are measured. By introducing each measured value into the following formula, the elastic recovery rate (%) of the compound layer is calculated.
Elastic recovery rate (%) = {(hmax−hp) / hmax} × 100.

  For the above test, a nanoindentation tester (“ENT-1100a”, manufactured by Elionix Co., Ltd.) and a Barcovic diamond indenter are used. When the coating 3 includes a layer other than the compound layer, the configuration of the coating 3 is confirmed in advance by SEM observation or the like, and the position of the compound layer is determined.

  In the compound layer satisfying the above (1), Ti is contained in an atomic ratio of 20% or more, and at least one of C and N is further contained. Such a compound layer can be excellent in hardness and excellent in heat resistance and chemical stability against high temperatures. Specifically, M is a group 4 element Zr, Hf, a group 5 element V, Nb, Ta, a group 6 element Cr, Mo, W, and Al, Si, and B. One or more elements selected from the group consisting of When M consists of one or more elements, the total amount of each element is less than 80% in atomic ratio.

  Here, as a general characteristic of the compound layer, there is a tendency that the toughness decreases when trying to increase the hardness (wear resistance), and there is a tendency that the hardness decreases when trying to increase the toughness. Are known.

  However, the compound layer according to the present embodiment can satisfy the above (2) in addition to the above (1). In other words, the compound layer according to the present embodiment can have excellent toughness (stickiness) while maintaining high hardness. Thus, in the compound layer according to the present embodiment, both high hardness and high toughness can be achieved.

  The reason why the compound layer according to this embodiment can be excellent in both properties of hardness and toughness is not clear, but it is presumed that at least a characteristic manufacturing method of the compound layer is involved.

  That is, in the conventional PVD method, when an arbitrary layer is formed on the base material 2, the bias voltage applied to the base material 2 is maintained constant or changes slowly and continuously (for example, The voltage was changed from 50 V to 150 V over 1 hour). On the other hand, unlike the conventional PVD method, the compound layer according to the present embodiment finely modulates the bias voltage applied to the substrate 2 when the compound layer is formed on the substrate 2.

  When a compound layer is produced by the PVD method in which the bias voltage is finely modulated, the layer grows unevenly. It is considered that the compound layer grown non-uniformly can have an excellent ability to relieve applied stress as compared to the compound layer grown uniformly. For this reason, the stress applied to an arbitrary position of the compound layer is diffused throughout the compound layer, and as a result, it is presumed that the elastic recovery rate of the compound layer is increased.

  As described above, the compound layer according to this embodiment has characteristics (hardness, heat resistance, chemical stability, etc.) that depend on the composition of (1) above and a high elastic recovery rate as described in (2) above. Both characteristics can be exhibited synergistically. For this reason, in the tool 1, not only are various properties such as hardness, heat resistance, chemical stability, etc. provided by the coating 3, but also the occurrence of defects like the conventional one due to having a high elastic recovery rate. The generation of cracks will be suppressed.

  Therefore, the tool 1 can be excellent in lifetime. Moreover, even if a crack is generated on the surface of the coating 3 in the tool 1, extension to the inside of the crack is suppressed due to the presence of the compound layer having an excellent elastic recovery rate. In the compound layer, the upper limit of the elastic recovery rate is not particularly limited, and the higher the elastic recovery rate, the higher the toughness. However, in consideration of manufacturability, 70% can be made the upper limit.

As understood from the above chemical formula, the compound layer detailed above includes a compound layer composed of a composition of Ti _x M _1-x C, a compound layer composed of a composition of Ti _x M _1-x CN, and Ti _x M _And a compound layer having a composition of _1-xN . Further, regarding the composition of the compound layer, preferably 0.2 ≦ x ≦ 0.7, and more preferably 0.3 ≦ x ≦ 0.7.

  The composition of the compound layer can be confirmed by using an EDX (Energy Dispersive X-ray spectroscopy) apparatus attached to the SEM or TEM. Specifically, first, as described above, an arbitrary position of the tool 1 is cut to prepare a sample including a cross section of the coating 3. Next, regarding the compound layer of the coating 3, an arbitrary region is analyzed using the above apparatus. Thereby, the atomic ratio of each element contained in an arbitrary region can be specified, and the composition of the compound layer is determined from this atomic ratio.

  Further, in the compound layer, M preferably contains at least one of Si and B. Various studies have confirmed that the elastic recovery rate of the compound layer is further improved in this case. Specifically, the elastic recovery rate can be 60% or more. In this case, the tool 1 can have a longer life.

  The reason why the elastic recovery rate is improved in the compound layer containing at least one of Si and B is not clear. However, from various examination results, it is considered that slight distortion occurs in the crystal structure of the compound layer when Si and / or B is contained in the compound layer mainly having a cubic crystal structure. It is inferred that the occurrence of such moderate strain is related to the improvement of the elastic recovery rate.

  The total content of Si and B in the compound layer is preferably 20% or less in terms of atomic ratio. If it exceeds 20%, the crystal structure of the compound layer changes from a cubic crystal structure to a hexagonal crystal structure, which may lead to a decrease in the hardness of the coating. Further, the lower limit of the total content is not particularly limited, but from the viewpoint of sufficiently exerting the effect of addition of these elements, the atomic ratio is preferably 0.5% or more, and is preferably 2 atomic% or more. More preferred.

  Further, in the compound layer, M preferably contains Al. In this case, the oxidation resistance of the compound layer can be improved. The Al content in the compound layer is preferably 30 to 70% in terms of atomic ratio. In this case, since the compound layer can be excellent in the balance of both properties of hardness and oxidation resistance, the life can be further extended.

  Especially, it is preferable that M is two types, Al and Si, or three types, Al, Si and B. In this case, the compound layer can be particularly excellent in the elastic recovery rate, and the friction stir welding tool can have a remarkable long life.

  From the viewpoint of avoiding a decrease in the hardness of the compound layer and maintaining a high hardness of the compound layer, the compound layer preferably does not contain a hexagonal crystal structure. In other words, the crystal structure of the compound layer is preferably a cubic crystal structure.

  Here, that the compound layer does not have a hexagonal crystal structure means that the hexagonal crystal structure is not detected when the compound layer is analyzed using an X-ray diffractometer. As the X-ray diffractometer, for example, “SmartLab (registered trademark)” manufactured by Rigaku Corporation can be used. The measurement conditions were a thin film method and an X-ray incident angle of θ to 2θ was 2 °.

Characteristic X-ray: Cu-Kα
Scanning speed: 0.2 ° / min Step: 0.05 °
Scan range: 20-80 °
Slit: PSA 0.228.

  The compound layer preferably has a thickness of 2 to 16 μm. Thereby, the said effect can be exhibited suitably, fully suppressing peeling of a compound layer. A more preferable thickness of the compound layer is 2.4 to 15 μm.

《Middle layer》
An intermediate | middle layer is a layer which exists between a base material and a compound layer. Such an intermediate layer preferably has a function of improving the adhesion between the compound layer and the substrate 2. However, the thickness of such an intermediate layer is preferably 4 μm or less. This is because if the thickness of the intermediate layer is large, the effect of suppressing defects and cracks by the compound layer tends to be suppressed. The lower limit value of the intermediate layer is not particularly limited, but is preferably 0.3 μm or more from the viewpoint of sufficiently exerting the effect.

<Surface layer>
The surface layer preferably has a function of improving the adhesion resistance of the coating 3 and / or a function of exhibiting color. Examples of the layer having a function of improving adhesion resistance include an AlN layer. Moreover, as a layer which has the function which exhibits a color, a TiN layer can be mentioned, for example.

<Friction stir welding tool manufacturing method>
The friction stir welding tool of the present embodiment can be manufactured through the following steps.

<< Base material preparation process >>
First, a base material is prepared in this step. The base material may be prepared by processing a commercially available base material into a desired shape, or may be prepared by sintering a raw material of the base material to produce a sintered body. A conventionally known method can be used as the sintering method.

<< Film formation process >>
Next, a film is formed on the surface of the substrate in this step. When the coating has a multilayer structure, for example, an intermediate layer, the compound layer and a surface layer, a desired coating can be formed on the substrate by laminating the layers in order from the layer side in contact with the substrate. it can.

The intermediate layer and the surface layer are produced by a conventionally known PVD method. Examples of the PVD method include an AIP method (ion plating method that evaporates a solid material using vacuum arc discharge) and a sputtering method. For example, when a TiN layer is manufactured using the AIP method, a Ti target that is a metal evaporation source and N ₂ that is a reactive gas may be used. When a TiN layer is manufactured using a sputtering method, a Ti target that is a metal evaporation source, N ₂ that is a reactive gas, and a sputtering gas such as Ar, Kr, or Xe may be used.

  On the other hand, the compound layer is manufactured by a PVD method such as an AIP method or a sputtering method, in which a bias voltage applied to the substrate is finely modulated. Specifically, when the compound layer is formed, a first application step in which a voltage having a single value (first voltage) is applied to the substrate for a certain period of time (first application time), A second application step in which a voltage (second voltage) of one value is applied for a certain time (second application time) is alternately repeated. As a result, the compound layer grows unevenly, and as described above, a compound layer having an excellent elastic recovery rate is produced.

  Based on various studies, the voltage difference between the first voltage and the second voltage is preferably 10 V or more. Thereby, the compound layer which satisfy | fills said (1) and (2) can be manufactured efficiently. When the voltage difference is increased, the elastic recovery rate of the compound layer tends to be improved. However, when the voltage difference is increased too much, there is a concern that the production stability is lowered. For this reason, it is necessary to confirm and determine the stability of the actual voltage concerning a base material.

For example, preferable production conditions when the AIP method is used are as follows.
Substrate temperature: 450-550 ° C
Gas: N ₂ gas, CH ₄ gas, etc. Pressure in the vacuum vessel: 1.5-6 Pa
Bias voltage (first voltage): -30 to -250V
Bias voltage (second voltage): -30 to -250V
Arc current: 100-250A
Difference between the first voltage and the second voltage: 10 to 100V.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these. In each of the following studies, a friction stir welding tool was manufactured, and the characteristics of each friction stir welding tool were confirmed.

<Examination 1>
<< No. 1 Manufacturing of friction stir welding tool >>
As follows, no. One friction stir welding tool was produced. First, a base material made of cemented carbide was prepared. Regarding the shape of the substrate, the probe portion had a diameter of 4.2 mm and a height of 2.5 mm. The cylindrical part had a diameter of 8 mm and a height of 15 mm. The characteristics of the cemented carbide are as follows.
Composition: 2.2% by mass of Co, 0.3% by mass of Cr, and balance of WC particles WC particles Average particle size: 1.0 μm.

Ion bombardment was performed on the base material under the following conditions. Thereby, the surface of the base material was cleaned.
Substrate temperature: 550 ° C
Gas: Pressure in Ar gas vacuum container: -1 Pa
Bias voltage: -500V
Processing time: 20 minutes.

A film formation process was performed on the base material after ion bombardment under the following conditions. Thereby, the compound layer was formed into a film on the surface of the base material.
Substrate temperature: 550 ° C
Gas: N ₂ gas target: Ti (70 atomic%), Al (30 atomic%)
Pressure in the vacuum vessel: 3.2 Pa
Bias voltage (first voltage): -55V
First application time: 1 second Bias voltage (second voltage): -70V
Second application time: 1 second Arc current: 120 A
Processing time: 90 minutes The first application step and the second application step are alternately repeated.

  After forming the film composed of the compound layer, the surface of the film was blasted with a soft medium with alumina abrasive grains. The processing time was 3 minutes.

As described above, No. 1 having a film composed of a compound layer having a thickness of 5 μm in the probe portion and a composition of Ti _0.7 Al _0.3 N. One friction stir welding tool was produced.

<< No. 2-No. Production of 15 friction stir welding tools >>
Other than changing the film forming conditions (type of target, type of gas, first voltage, second voltage, first application time, second application time, and processing time) and forming a compound layer having the composition shown in Table 1 No. 1 was used to produce a friction stir welding tool. Table 1 shows the composition of each compound layer and the film forming conditions (first voltage, second voltage, and each application time). In addition, the processing time in each friction stir welding tool was adjusted so that the thickness of the compound layer in the probe portion was 5 μm. In the column of “first voltage (second) / second voltage (second)” in Table 1, the value of the first voltage, the application time (second) of applying the first voltage, the value of the second voltage, and the second The application time (seconds) during which the voltage is applied is described in this order from the left side.

<Measurement of elastic recovery rate>
According to the above-mentioned method, hmax and hp of each compound layer were measured, and thereby the elastic recovery rate was obtained. The results are shown in Table 1.

《Joint test》
Using each friction stir welding tool, a steel plate spot joining (FSJ) test was performed. The joining conditions are shown below.
Joined material: 1200MPa class high-tensile steel plate (thickness: 1.5mm) 2 tools piled up: 1100rpm
Bonding load: 2000kgf
Joining time: 4 seconds.

  The above joining was repeated, and observation of the coating film at the contact portion with a microscope was performed every 50 spots. When the occurrence of cracks in the coating was confirmed, the joining test was stopped, and the number of spots produced until the stop was measured. The results are shown in Table 1. In Table 1, in the friction stir welding tool indicated by (* 1) after the number of spots, the joining test was stopped when the coating was worn and disappeared without cracking. The number of spots is shown.

<Evaluation>
As shown in Table 1, No. 1 having a compound layer satisfying the above (1) and (2). 1-No. No. 11 which does not satisfy the above (1) and / or the above (2). 12-No. More spots could be made than 15 friction stir welding tools. That is, no. 1-No. Eleven friction stir welding tools could have a long life.

  No. 1-No. 11 was confirmed to have a longer life when the elastic recovery rate exceeds 60%. Furthermore, no. 8-No. From the result of 11, it was confirmed that the compound layer has a particularly long life when it contains Si and / or B. No. 6 and no. 8 to 11 were compared, and it was confirmed that Al was preferably contained.

<Examination 2>
<< No. 16-No. Manufacture of 20 friction stir welding tools >>
As a substrate made of cemented carbide, a cemented carbide having the following characteristics is used, and film formation conditions (type of target, type of gas, first voltage, second voltage, first application time, second application time, And treatment time), and a compound layer having the composition shown in Table 2 was formed. 1 was used to produce a friction stir welding tool.
Composition: 2.2% by mass of Co, 0.3% by mass of Cr, and balance of WC particles WC particles Average particle size: 0.8 μm
Vickers hardness Hv: 16.5 GPa
Fracture toughness K _1c : 6.4 MPa · m ^1/2 .

<< No. 21-No. Production of 23 friction stir welding tools >>
Except that an intermediate layer was formed between the substrate and the compound layer by the following method, No. 16-No. In the same manner as in No. 20, a friction stir welding tool was manufactured. The thickness of the intermediate layer was adjusted as shown in Table 2 by changing the treatment time.
Substrate temperature: 550 ° C
Gas: N ₂ gas target: Ti
Pressure in the vacuum vessel: 3.2 Pa
Bias voltage: -100V
Arc current: 120A.

<< No. 24 and no. Production of 25 friction stir welding tools >>
As a base material made of cemented carbide, No. 1 was used except that a cemented carbide having the following characteristics was used. 16-No. In the same manner as in No. 20, a friction stir welding tool was manufactured.
Composition: 4.0% by mass of Co, 0.3% by mass of Cr, and balance of WC particles WC particles Average particle size: 0.9 μm
Vickers hardness Hv: 15.2 GPa
Fracture toughness K _1c : 8.1 MPa · m ^1/2 .

<Measurement of elastic recovery rate>
According to the above-mentioned method, hmax and hp of each compound layer were measured, and thereby the elastic recovery rate was obtained. The results are shown in Table 2.

《Joint test》
Using each friction stir welding tool, a simulated joining test simulating spot joining (FSJ) of steel plates was performed. The joining conditions are shown below.
Joined material: 980 MPa class high-tensile steel plate (thickness: 4 mm) 1 tool rotation speed: 1450 rpm
Bonding load: 1500kgf
Joining time: 4.5 seconds.

  The simulated joining was repeated, and the coating at the contact portion was observed with a microscope every 50 spots. When the occurrence of cracks in the coating was confirmed, the joining test was stopped, and the number of spots produced until the stop was measured. The results are shown in Table 2. In Table 2, in the friction stir welding tool in which (* 1) is shown after the number of spots, the joining test was stopped when the coating was worn and disappeared without cracking. In the friction stir welding tool indicated by (* 2) behind the spot, the joining test was stopped when the film peeled off.

<Evaluation>
No. 16-No. 20, it was confirmed that the thickness of the compound layer is preferably larger than 1.6 μm and smaller than 17.5 μm. From this, it can be said that the preferable range of the compound layer is 2 to 16 μm.

  No. 21-No. 23, a decrease in the number of spots was observed when the thickness of the intermediate layer was 4.5 μm. From this, it can be said that when the coating has an intermediate layer, the thickness of the intermediate layer is preferably 4 μm or less.

  Moreover, the base material has a Vickers hardness of 16 GPa or more and a fracture toughness value of 7.0 or less. 16 and no. From each of the 18 results, it was found that the increase in the lifetime due to the thickness of the compound layer being within the above range was remarkable. On the other hand, no. 24 and no. From each result of 25, it was found that the increase in the lifetime due to the thickness of the compound layer being in the above range is not remarkable as compared with the former. From this, it was confirmed that when the substrate has a Vickers hardness of 16 GPa or more and a fracture toughness value of 7.0 or less, the lifetime tends to be improved efficiently.

<Examination 3>
<< No. 26 and no. Production of 27 tools for friction stir welding >>
As a substrate made of cemented carbide, a cemented carbide having the following characteristics is used, and film formation conditions (type of target, type of gas, first voltage, second voltage, first application time, second application time, And the treatment time), and a compound layer having the composition shown in Table 3 was formed. 1 was used to produce a friction stir welding tool.
Composition: 2.5% by mass of Co, 0.2% by mass of Cr, and balance of WC particles WC particles Average particle size: 1.1 μm.

<Measurement of elastic recovery rate>
According to the above-mentioned method, hmax and hp of each compound layer were measured, and thereby the elastic recovery rate was obtained. The results are shown in Table 3.

《Joint test》
Using each friction stir welding tool, a simulated joining test simulating spot joining (FSJ) of steel plates was performed. The joining conditions are shown below.
Material to be joined: 980 MPa class high-tensile steel plate (thickness: 4 mm) 1 tool rotation speed: 1500 rpm
Bonding load: 1480kgf
Joining time: 6 seconds.

  The simulated joining was repeated, and the coating at the contact portion was observed with a microscope every 50 spots. When the occurrence of cracks in the coating was confirmed, the joining test was stopped, and the number of spots produced until the stop was measured. The results are shown in Table 3.

<Confirmation of crystal structure>
Using an X-ray diffractometer (“SmartLab (registered trademark)”, manufactured by Rigaku Corporation), whether or not a hexagonal crystal structure exists in the compound layer was confirmed by the method described above. The results are shown in Table 3. In Table 3, “Yes” means that a hexagonal crystal structure was detected, and “No” means that no hexagonal crystal structure was detected.

<Evaluation>
No. 26 and no. 27 and No. 27. 26 was capable of forming more spots. From this, it was found that the compound layer preferably does not contain a hexagonal crystal structure.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is shown not by the embodiments and examples described above but by the scope of claims, and is intended to include meanings equivalent to the scope of claims and all modifications within the scope.

DESCRIPTION OF SYMBOLS 1 Friction stir welding tool 2 Base material 3 Coating 4 Probe part 5 Column part 6 Shoulder part 7 Chuck part.

Claims (6)

A friction stir welding tool comprising a base material and a coating film covering the surface of the base material,
The coating is Ti _x M _{1-x Cy} N _1-y (M is one or more selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, Al, Si and B in the periodic table) Including a compound layer composed of an element (excluding Ti, satisfying 0.2 ≦ x ≦ 1 and 0 ≦ y ≦ 1),
The friction stir welding tool, wherein the compound layer has an elastic recovery rate of 52% or more.   The friction stir welding tool according to claim 1, wherein M includes at least one of Si and B.   The friction stir welding tool according to claim 1 or 2, wherein the compound layer does not include a hexagonal crystal structure.   The friction stir welding tool according to any one of claims 1 to 3, wherein the compound layer has a thickness of 2 µm to 16 µm. The coating includes an intermediate layer between the substrate and the compound layer,
The friction stir welding tool according to any one of claims 1 to 4, wherein the intermediate layer has a thickness of 4 µm or less. The friction stir welding tool according to any one of claims 1 to 5, wherein the base material has a Vickers hardness of 16 GPa or more and a fracture toughness value of 7.0 MPa · m ^1/2 or less.

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