JP7451350B2 - End mills and friction stir welding tools - Google Patents

Description

The present disclosure relates to an end mill and a friction stir welding tool.

Silicon nitride sintered bodies made of silicon nitride or sialon have better thermal shock resistance than other ceramic sintered bodies, and better heat and reaction resistance than metal materials, and are used in friction stir welding tools and other materials. It is used as a cutting tool (see Patent Document 1 and Patent Document 2).

Japanese Patent Application Publication No. 2019-198895 Japanese Patent Application Publication No. 2002-307208

Incidentally, in recent years, there has been a demand for higher efficiency in machining using the above-mentioned tools, and further improvement in the durability of the tools is desired.
End mills require high feed rates for cutting to increase efficiency. However, increasing the feed rate during cutting increases the load on the tool in the feed direction, making the tool more likely to break.
Friction stir welding tools require high-speed welding to achieve high efficiency. However, increasing the joining speed increases the tool load due to insufficient heat input, making the tool more likely to break.
The present disclosure has been made in view of the above circumstances, and aims to provide an end mill and a friction stir welding tool with improved fracture resistance. The present disclosure can be realized as the following forms.

[1] An end mill made of a silicon nitride sintered body containing silicon nitride or sialon as a main component,
The silicon nitride sintered body has an end face and an outer circumferential face continuous with the end face,
The silicon nitride sintered body contains at least one of β silicon nitride and β sialon,
Among the XRD peaks of the silicon nitride sintered body, the peak intensity I (200) attributed to the crystal plane (200) of the β silicon nitride and/or the β sialon, and the peak intensity I (200) of the β silicon nitride and/or The peak intensity I(002) attributed to the crystal plane (002) of the β-sialon satisfies the following relational expression [1] when observed from the outer circumferential surface, and the following when observed from the end face: An end mill that satisfies relational expression [2].

Relational expression [1]: 0.80≦I(200)/(I(200)+I(002))≦1.00
Relational expression [2]: 0.50≦I(200)/(I(200)+I(002))≦0.70

[2] The end mill according to [1], wherein the silicon nitride sintered body has a bending strength at 1000°C that is 90% or more of the bending strength at 25°C.

[3] The end mill according to [1] or [2], wherein a coating layer is formed on the surface.

[4] A friction stir welding tool composed of a silicon nitride sintered body containing silicon nitride or Sialon as a main component,
The silicon nitride sintered body has an end face and an outer circumferential face continuous with the end face,
The silicon nitride sintered body contains at least one of β silicon nitride and β sialon,
Among the XRD peaks of the silicon nitride sintered body, the peak intensity I (200) attributed to the crystal plane (200) of the β silicon nitride and/or the β sialon, and the peak intensity I (200) of the β silicon nitride and/or The peak intensity I(002) attributed to the crystal plane (002) of the β-sialon satisfies the following relational expression [1] when observed from the outer peripheral surface, and the following when observed from the end face: A friction stir welding tool that satisfies relational expression [2].

Relational expression [1]: 0.80≦I(200)/(I(200)+I(002))≦1.00
Relational expression [2]: 0.50≦I(200)/(I(200)+I(002))≦0.70

[5] The friction stir welding tool according to [4], wherein the silicon nitride sintered body has a bending strength at 1000°C that is 90% or more of the bending strength at 25°C.

[6] The friction stir welding tool according to [4] or [5], wherein a coating layer is formed on the surface.

By satisfying the above relational expressions [1] and [2], the fracture resistance of the end mill is improved.
When the bending strength at 1000°C of the silicon nitride sintered body is 90% or more of the bending strength at 25°C, the thermal shock resistance of the end mill is improved.
When a coating layer is formed on the surface, the wear resistance of the end mill is improved.
By satisfying the above relational expressions [1] and relational expressions [2], the fracture resistance of the friction stir welding tool is improved.
When the bending strength at 1000°C of the silicon nitride sintered body is 90% or more of the bending strength at 25°C, the thermal shock resistance of the friction stir welding tool is improved.
When a coating layer is formed on the surface, the wear resistance of the friction stir welding tool is improved.

It is a side view of an end mill. FIG. 3 is a diagram schematically showing the orientation of β silicon nitride and/or β sialon on the outer peripheral surface. It is a front view of an end mill. FIG. 3 is a diagram schematically showing the orientation of β silicon nitride and/or β sialon on an end face. It is a figure which shows the X-ray diffraction pattern in the outer peripheral surface of an Example. FIG. 2 is a side view of a friction stir welding tool. It is a front view of a tool for friction stir welding. It is a perspective view explaining the usage state of the tool for friction stir welding. 2 is a graph showing changes in temperature and press pressure in the firing process of Examples 1 to 10. 3 is a graph showing changes in temperature and press pressure in the firing process of Comparative Examples 1 and 2.

The present disclosure will be described in detail below. In this specification, descriptions using "~" for numerical ranges include the lower limit and upper limit unless otherwise specified. For example, the description "10 to 20" includes both the lower limit value of "10" and the upper limit value of "20". That is, "10 to 20" has the same meaning as "10 or more and 20 or less".

1. End Mill The end mill 10 is composed of a silicon nitride sintered body 11 containing silicon nitride or sialon as a main component. The silicon nitride sintered body 11 has an end surface 20 and an outer circumferential surface 30 continuous to the end surface 20. The silicon nitride sintered body 11 contains at least one of β silicon nitride and β sialon.
Among the XRD (X-ray diffraction) peaks of the silicon nitride sintered body 11, the end mill 10 has a peak intensity I (200) assigned to the crystal plane (200) of β silicon nitride and/or β sialon. , the peak intensity I(002) attributed to the crystal plane (002) of β silicon nitride and/or β SiAlON satisfies the following relational expression [1] when observed from the outer circumferential surface 30, and when viewed from the end surface 20. When observed, the following relational expression [2] is satisfied.

Relational expression [1]: 0.80≦I(200)/(I(200)+I(002))≦1.00
Relational expression [2]: 0.50≦I(200)/(I(200)+I(002))≦0.70

(1) Configuration of end mill As shown in FIGS. 1 and 3, the end mill 10 is a substantially cylindrical cutting tool made of a silicon nitride sintered body 11. The central axis of the silicon nitride sintered body 11 is referred to as an axis X1.
The silicon nitride sintered body 11 has an end surface 20 and an outer circumferential surface 30 continuous to the end surface 20. The end surface 20 is located on the front end side of the silicon nitride sintered body 11. When the silicon nitride sintered body 11 is cut along a plane that passes through the corner 22 and includes the axis X1, the end surface 20 and the outer circumferential surface 30 are substantially perpendicular to each other in the cut surface.

A bottom blade 21 is provided on the end surface 20. The bottom blade 21 is formed radially outward from the vicinity of the axis X1. The outer peripheral surface 30 is provided with an outer peripheral blade 31 and a chip discharge groove 32. The outer peripheral cutter 31 is connected to the bottom cutter 21 via the corner 22. The peripheral blade 31 is formed in a plurality of strips (for example, four strips) from the front end side (lower side in FIG. 1) to the rear end side of the silicon nitride sintered body 11 so as to be twisted rearward in the rotational direction of the axis X1. has been done. The plurality of outer peripheral blades 31 are formed at equal intervals in the circumferential direction. The chip discharge groove 32 is formed between the adjacent peripheral blades 31 so as to be twisted rearward in the rotational direction of the axis X1 from the front end side to the rear end side.

The end mill 10 is used by being attached to a cutting device (not shown). The end mill 10 receives pressure from a cutting device, is pushed into a cut member (not shown) in the direction of an axis X1 while rotating, and is sent out in a direction perpendicular to the direction of the axis X1. Then, the member to be cut is cut by the bottom blade 21 and the outer peripheral blade 31. That is, the end surface 20 of the end mill 10 is located in the direction of pushing into the workpiece. The outer circumferential surface 30 of the end mill 10 is located in the feeding direction (movement direction) of the end mill 10.

(2) Components contained in the silicon nitride sintered body The silicon nitride sintered body 11 has silicon nitride or sialon as a main component. Here, the main component refers to a component whose content (mass%) is 50% by mass or more. The main component of the silicon nitride sintered body 11 may be silicon nitride (Si ₃ N ₄ ), or may be sialon in which part of the Si or N of Si ₃ N ₄ is replaced with Al or oxygen. good. The silicon nitride sintered body 11 has a main crystal phase composed of silicon nitride or sialon bonded together by a bonding phase.

The silicon nitride sintered body 11 contains at least one of β silicon nitride and β sialon. βsialon is represented by, for example, the composition formula Si _6-Z Al _Z O _Z N _8-Z (0<Z≦4.2). β silicon nitride or β sialon has a needle-like particle shape and therefore has high toughness. In the silicon nitride sintered body 11, the ratio of β silicon nitride or β sialon to the total silicon nitride or sialon is not particularly limited.
The silicon nitride sintered body 11 may contain α silicon nitride in addition to β silicon nitride as silicon nitride. The silicon nitride sintered body 11 may contain α-sialon in addition to β-sialon. Since alpha silicon nitride or alpha sialon has an equiaxed particle shape, it has lower toughness than beta silicon nitride or beta sialon, but has higher hardness.

The silicon nitride sintered body 11 contains rare earth elements used as sintering aids, such as scandium (Sc), yttrium (Y), dysprosium (Dy), ytterbium (Yb), erbium (Er), and cerium (Ce). and lutetium (Lu). The content of these elements is not particularly limited. The content of these elements may be 1% by mass or more and 7% by mass or less in terms of oxide, based on the silicon nitride sintered body 11 . Note that oxide conversion means conversion to an oxide combined with oxygen.
Among these, the silicon nitride sintered body 11 preferably contains yttrium (Y) from the viewpoint of having excellent high-temperature properties.

The silicon nitride sintered body 11 is made of a hard material such as silicon carbide (SiC), titanium nitride (TiN), titanium carbonitride (TiCN), titanium carbide (TiC), or tungsten carbide (WC), in addition to silicon nitride or Sialon. It may contain carbonitride. The content of hard carbonitrides is not particularly limited. The content of hard carbonitride may be, for example, 1% by mass or more and 7% by mass or less based on the silicon nitride sintered body 11.
Among these, silicon nitride sintered body 11 preferably contains silicon carbide (SiC) from the viewpoint of excellent high-temperature properties.

(3) Relational expression between I(200) and I(002) Here, the relational expression between I(200) and I(002) will be explained. FIG. 5 shows an X-ray diffraction pattern on the outer peripheral surface of one example.
When the silicon nitride sintered body 11 contains β-silicon nitride, the peak intensity I (200) is equal to the peak attributable to the crystal plane (200) among the XRD peaks of β-silicon nitride. It is strength. For example, a peak height near 2θ=27.0° is preferably used. The peak intensity I (002) is the intensity of the peak attributed to the crystal plane (002) among the XRD peaks of β silicon nitride. For example, a peak height near 2θ=63.9° is preferably used.
When the silicon nitride sintered body 11 contains β-sialon, the peak intensity I (200) is the intensity of the peak attributed to the crystal plane (200) among the XRD peaks of β-sialon. be. For example, a peak height near 2θ=27.3° is preferably used. The peak intensity I (002) is the intensity of the peak attributed to the crystal plane (002) among the XRD peaks of β-sialon. For example, a peak height near 2θ=64.1° is preferably used.
When the silicon nitride sintered body 11 contains both β-silicon nitride and β-sialon, the peak attributed to the crystal plane (200) of β-silicon nitride and β-sialon and the crystal plane (002) The assigned peaks overlap in position closely. In this case, among the XRD peaks of β-silicon nitride and β-sialon, the intensity of the peak attributed to the crystal plane (200), for example, the peak height near 2θ=27.0°, is calculated as the peak intensity I(200 ) can be adopted as Among the XRD peaks of β-silicon nitride and β-sialon, the intensity of the peak attributed to the crystal plane (002), for example, the peak height near 2θ = 64.0°, is adopted as the peak intensity I (002). I can do it.
Note that if it is not easy to determine whether the silicon nitride sintered body 11 contains only one or both of β-silicon nitride and β-sialon, it may be assumed that it contains both.

The peak intensities I (200) and I (002) satisfy the above relational expressions [1] and [2], but preferably satisfy the following relational expressions [1'] and [2'].

Relational expression [1']:
0.86≦I(200)/(I(200)+I(002))≦1.00
Relational expression [2']:
0.55≦I(200)/(I(200)+I(002))≦0.65

When the peak intensity ratio I(200)/(I(200)+I(002)) is 1.00, the long axis of all β-silicon nitride or β-sialon crystal grains (hereinafter also referred to as c-axis) is on the measurement plane. means parallel to. When I(200)/(I(200)+I(002)) is 0.00, it means that the long axis of all β silicon nitride or β sialon crystal grains is perpendicular to the measurement plane. .

Let X be the value of I(200)/(I(200)+I(002)) when observed from the outer peripheral surface 30, and I(200)/(I(200)+I(002) when observed from the end surface 20) ), it is preferable that X−Y≧0.12 be satisfied.

FIG. 2 schematically shows the orientation of β silicon nitride and/or β sialon on the outer peripheral surface 30. The Z-axis direction in FIG. 2 coincides with the Z-axis direction in FIG. 1 (axis X1 direction of the end mill 10). FIG. 4 schematically shows the orientation of β silicon nitride and/or β sialon on the end face 20. The X-axis direction and the Y-axis direction in FIG. 4 are perpendicular to the Z-axis direction in FIGS. 1 and 2.
In a configuration that satisfies the above relational expressions [1] and [2], as shown in FIGS. 2 and 4, crystal grains of β silicon nitride and/or β sialon are preferentially oriented in the Z-axis direction.

In order to control the orientation of crystal grains of β-silicon nitride or β-sialon so as to satisfy the above relational expressions [1] and [2], the method described in “2. Orientation control of β-silicon nitride or β-sialon” described below is necessary. is preferably adopted. According to this method, when the crystal grains of β-silicon nitride or β-sialon grow in the c-axis direction, the growth direction is controlled, and the crystal grains of β-silicon nitride or β-sialon are grown in the silicon nitride sintered body 11. The orientation of crystal grains is controlled.

(4) Bending strength of silicon nitride sintered body From the viewpoint of improving thermal shock resistance, the silicon nitride sintered body 11 should have a bending strength at 1000°C of 90% or more of the bending strength at 25°C. is preferable, more preferably 92% or more, and still more preferably 94% or more. The bending strength at 1000°C relative to the bending strength at 25°C is usually 100% or less.
The bending strength of the silicon nitride sintered body 11 can be measured using a test piece with a total length of 40 mm, width of 4 mm, and thickness of 3 mm. The bending strength at 25° C. can be measured by a room temperature bending strength test method for fine ceramics (3-point bending method, span 30 mm) according to JIS R 1601. The bending strength at 1000° C. can be measured by a high temperature bending strength test method for fine ceramics (3-point bending method, span 30 mm) according to JIS R 1604.

The bending strength at 1000° C. of the silicon nitride sintered body 11 is preferably 980 MPa or more, more preferably 1000 MPa or more, and even more preferably 1030 MPa or more, from the viewpoint of improving thermal shock resistance. . The upper limit of the bending strength of the silicon nitride sintered body 11 at 1000° C. is, for example, 1200 MPa.
The bending strength of the silicon nitride sintered body 11 at 1000° C. can be improved, for example, by adding a hard carbonitride having excellent high-temperature properties.

(5) Coating layer It is preferable that the end mill 10 has a coating layer formed on its surface. The coating layer is made of at least one carbide, nitride, oxide, carbonitride, carbonate, nitride, and carbonitoxide selected from the group consisting of titanium, chromium, and aluminum. It may be a surface coating layer.
When the coating layer is formed, the surface hardness of the end mill 10 increases, and the progression of wear due to reaction and welding with the workpiece is suppressed. As a result, the wear resistance of the end mill 10 is improved.
The at least one compound selected from carbides, nitrides, oxides, carbonitrides, carbonates, nitrides, and carbonitoxides of titanium, chromium, and aluminum includes, but is not particularly limited to, TiN, Suitable examples include TiAlN, TiAlCrN, and AlCrN.
The thickness of the coating layer is not particularly limited. From the viewpoint of wear resistance, the thickness of the coating layer is preferably 0.02 μm to 30 μm, more preferably 0.05 μm to 20 μm, and even more preferably 0.1 μm to 10 μm.

2. Orientation control of crystal grains of β silicon nitride or β sialon In the end mill 10, the orientation of crystal grains of β silicon nitride or β sialon is controlled, and the above relational expressions [1] and [2] are satisfied.
The orientation of crystal grains of β silicon nitride or β sialon can be controlled, for example, as follows. That is, by controlling the pressure conditions and heating conditions in pressure firing such as hot pressing and spark plasma sintering (SPS), the orientation of the crystal grains of β silicon nitride or β sialon can be controlled. .
For example, the orientation of crystal grains is controlled as follows. Conventionally, when manufacturing the end mill 10, a firing process (main firing process) in which firing is performed at a predetermined temperature under a predetermined press pressure has been employed. On the other hand, in order to control the orientation of the crystal grains, prior to this firing process (main firing process), preliminary firing is performed in which firing is performed at a pressure lower than the predetermined press pressure and at a temperature lower than the predetermined temperature. By providing this process, the orientation of crystal grains can be controlled. Further, in conventional firing, press pressure is not applied when the temperature is lowered from the firing process, but press pressure may be applied when the temperature is lowered. Orientation of crystal grains is further promoted by press pressure during cooling.
Note that the pressure applied during the preliminary firing process is changed as appropriate depending on the size, shape, etc. of the end mill 10. In the pre-firing process, for example, a temperature range of 1300° C. to 1500° C., a pressure of 5 MPa to 15 MPa using the outer circumferential surface 30 of the end mill 10 as the pressing surface, and a pressing time of 1 hour to 4 hours are preferably employed.

3. Estimated reason why the end mill has excellent fracture resistance Here, the presumed reason why the end mill 10 of the present disclosure has excellent fracture resistance will be explained. In addition, in the following description, "I(200)/(I(200)+I(002))" is also referred to as "peak intensity ratio."
By satisfying relational expression [1] and relational expression [2], the durability against the load applied to the outer peripheral surface 30 increases. This is thought to be because silicon nitride or sialon grows in a needle-like orientation in the plane direction of the outer circumferential surface 30 (Z-axis direction in FIGS. 1 and 2), and a bridging effect (wedge effect) acts on the outer circumferential surface 30. .
If there is no such oriented growth, the peak intensity ratio when observed from the outer peripheral surface 30 would be less than 0.8, and the peak intensity ratio when observed from the end surface 20 would be greater than 0.7, resulting in a bridging effect. It is thought that due to the insufficient amount, the outer circumferential surface 30 cannot withstand the load, leading to breakage of the end mill 10.
On the other hand, if the orientation progresses too much, the peak intensity ratio when observed from the end face 20 becomes less than 0.5, and it is presumed that the fracture resistance of the end face 20 decreases. That is, in this case, the bridging effect of the end face 20 is almost eliminated, the strength of the end face 20 is insufficient, and the end mill 10 is considered to be damaged.

4. Friction Stir Welding Tool The friction stir welding tool 110 is composed of a silicon nitride sintered body 111 containing silicon nitride or sialon as a main component. The silicon nitride sintered body 111 has an end surface 120 and an outer circumferential surface 130 continuous with the end surface 120. The silicon nitride sintered body 111 contains at least one of β silicon nitride and β sialon.
The friction stir welding tool 110 has a peak intensity I (200) attributed to the crystal plane (200) of β silicon nitride and/or β sialon among the XRD peaks of the silicon nitride sintered body 111, and β The peak intensity I (002) attributed to the crystal plane (002) of silicon nitride and/or β-sialon satisfies the following relational expression [1] when observed from the outer peripheral surface 130 and when observed from the end surface 120. In this case, the following relational expression [2] is satisfied.

Relational expression [1]: 0.80≦I(200)/(I(200)+I(002))≦1.00
Relational expression [2]: 0.50≦I(200)/(I(200)+I(002))≦0.70

(1) Configuration of Friction Stir Welding Tool The friction stir welding tool 110 is a substantially cylindrical welding tool made of a silicon nitride sintered body 111, as shown in FIGS. 6 and 7. The central axis of the silicon nitride sintered body 111 is referred to as an axis X2. The silicon nitride sintered body 111 has an end surface 120 and an outer circumferential surface 130 continuous with the end surface 120. The end surface 120 is located on the front end side of the silicon nitride sintered body 111. When the silicon nitride sintered body 111 is cut along a plane including the axis X1, the end face 120 and the outer circumferential face 130 are substantially orthogonal to each other in the cut plane.

The silicon nitride sintered body 111 includes a shaft portion 112 and a projection portion 113. The shaft portion 112 is formed into a substantially cylindrical shape extending in the direction of the axis X2. The protrusion 113 is formed in a substantially cylindrical shape and is provided so as to protrude forward from a surface (also referred to as a shoulder portion) that is substantially perpendicular to the axis X2 at the front end portion of the shaft portion 112. The protruding portion 113 is formed at the center of the shoulder portion, and the axis of the protruding portion 113 coincides with the axis X2 of the shaft portion 112. An example of the end surface 120 of the silicon nitride sintered body 111 is the end surface of the protrusion 113. An example of the outer circumferential surface 130 of the silicon nitride sintered body 111 is the outer circumferential surface of the protrusion 113.

FIG. 8 is a diagram illustrating a usage state of the friction stir welding tool 110. The friction stir welding tool 110 is used by being attached to a welding device (not shown). The protrusion 113 of the friction stir welding tool 110 receives pressure from the welding device and is pushed into the welding line WL, which is the boundary between the members 114 and 115 to be welded, while rotating. Then, with the protrusion 113 being pushed into the welded members 114, 115, the welded members 114, 115 are moved relative to the friction stir welding tool 110 in the direction shown by the white arrow in the figure. Moving. Thereby, the friction stir welding tool 110 moves relatively along the welding line WL. In this embodiment, the members 114 and 115 to be joined are steel plates, but they may be made of any other metal instead of steel. The vicinity of the joining line WL of the members 114 and 115 to be joined plastically flows due to the frictional heat between them and the protrusion 113. The protruding portion 113 stirs the plastically fluidized portions of the members 114 and 115 to be joined, thereby forming the joining area WA. The members to be joined 114 and 115 are joined to each other by this joining area WA. That is, the end surface 120 of the friction stir welding tool 110 is located in the direction of pushing into the members 114 and 115 to be welded. The outer peripheral surface 130 of the friction stir welding tool 110 is located in the direction of movement of the friction stir welding tool 110 with respect to the members 114 and 115 to be welded.

In addition, in the friction stir welding tool 110, the components contained in the silicon nitride sintered body 111, the relational expressions of I(200) and I(002), the coating layer, and the orientation control of the crystal grains of β silicon nitride or β Sialon. Regarding the end mill 10 described above, "(2) Components contained in the silicon nitride sintered body", "(3) relational expression of I(200) and I(002)", "(4) coating layer", This is the same as "2. Orientation control of crystal grains of β silicon nitride or β sialon", and the explanation will be omitted.

5. Estimated reason why the friction stir welding tool has excellent fracture resistance Here, the presumed reason why the friction stir welding tool 110 of the present disclosure has excellent fracture resistance will be explained. In addition, in the following description, "I(200)/(I(200)+I(002))" is also referred to as "peak intensity ratio."
By satisfying relational expression [1] and relational expression [2], the durability against the load applied to the outer peripheral surface 130 increases. This is considered to be because silicon nitride or sialon grows in a needle-like orientation in the plane direction of the outer circumferential surface 130 (Z-axis direction in FIG. 6), and a bridging effect (wedge effect) acts on the outer circumferential surface 130.
If there is no such oriented growth, the peak intensity ratio when observed from the outer circumferential surface 130 would be less than 0.8, and the peak intensity ratio when observed from the end surface 120 would be greater than 0.7, resulting in a bridging effect. For example, if the degree of softening of the welded members 114, 115 is low due to insufficient heat input, the outer circumferential surface 130 cannot withstand the load, and the friction stir welding tool 110 may break. Conceivable.
On the other hand, if the orientation progresses too much, the peak intensity ratio when observed from the end face 120 becomes less than 0.5, and it is presumed that the fracture resistance of the end face 120 decreases. That is, in this case, the bridging effect of the end face 120 is almost eliminated, the strength of the end face 120 is insufficient, and the friction stir welding tool 110 is considered to be damaged.

In the following experiments, each of the silicon nitride sintered bodies of Examples 1 to 10 and Comparative Examples 1 to 4 was produced, and each of these silicon nitride sintered bodies was processed to produce the results of Examples 1 to 10 and Comparative Examples. End mills 1 to 4 and tools for friction stir welding were used.

1. Preparation of silicon nitride sintered body (1) Blend Table 1 shows the formulation (% by mass) of the raw material powder used for the silicon nitride sintered body of each example and comparative example. Aluminum oxide (Al ₂ O ₃ ) and aluminum nitride (AlN) have been used for sialonization of α-silicon nitride (α-Si ₃ N ₄ ). Yttrium oxide (Y ₂ O ₃ ) is an auxiliary agent for improving the sinterability of the silicon nitride sintered body 11 .
In addition, the raw material powder is shown below.
α-Si ₃ N ₄ powder: average particle size 0.1 μm
_{Al2O3 powder} : average particle size 0.5μm
AlN powder: average particle size 1.0 μm
_{Y2O3 powder} : average particle size 0.8μm
β-SiC powder: average particle size 0.8 μm

(2) Mixing and Drying Raw material powder and ethanol were placed in a resin pot, and mixed and pulverized for 24 hours. After mixing and pulverizing, the slurry was dried in a hot water bath to remove the ethanol and obtain a dry mixed powder.
Note that the steps up to this point are common to the silicon nitride sintered bodies of all Examples and Comparative Examples.

(3) Firing (3-1) Silicon nitride sintered bodies of Examples 1 to 10 The silicon nitride sintered bodies of Examples 1 to 10 were hot-press fired by the following method to form silicon nitride sintered bodies. I got it.
The mixed powder was fired under the following conditions in a nitrogen atmosphere of 3 atm. FIG. 9 shows the temperature and press pressure during hot press firing. The mixed powder was held at 1430°C for 2 hours during heating before reaching the firing temperature (1600°C to 1830°C). While the temperature was maintained at 1430° C., a pressure of 10 MPa was applied using the outer circumferential surface as a pressing surface (first press treatment). Thereafter, the temperature was raised and maintained at the firing temperature for 1.5 hours. During the temperature rise after the first press treatment and while being maintained at the firing temperature, a pressure of 35 MPa was applied with the outer circumferential surface as the press surface. After completion of the holding at the firing temperature, the pressurization of 35 MPa was continued for about 4 hours while the temperature was lowered from the firing temperature to 1430° C., with the outer circumferential surface being used as the pressing surface.
In the manner described above, silicon nitride sintered bodies of Examples 1 to 10 were obtained.
Note that "HP" in "Firing method" in Table 1 means that hot press firing was performed. "Presence" in "Presence or absence of first press treatment" in Table 1 means that "pressure was applied while keeping the temperature approximately constant in a temperature range lower than the firing temperature during temperature rise and fall." Moreover, "none" means "pressure was not applied while keeping the temperature approximately constant in a temperature range lower than the firing temperature during temperature raising and lowering".

(3-2) Silicon nitride sintered bodies of Comparative Examples 1 and 2 The silicon nitride sintered bodies of Comparative Examples 1 and 2 were different from the silicon nitride sintered bodies of Examples 2 and 4 until drying and granulation. Although it is the same, it differs from the silicon nitride sintered bodies of Examples 2 and 4 in that it is not pressurized in a temperature range lower than the firing temperature (here, 1430° C.). In addition, the silicon nitride sintered bodies of Comparative Examples 1 and 2 were different from those of Examples 1 to 10 in that no pressure was applied while the temperature was lowered from the sintering temperature to 1430°C after the holding at the sintering temperature was completed. It is different from silicon sintered body. That is, Comparative Examples 1 and 2 employ the conventional hot press firing.
FIG. 10 shows the temperature and press pressure in this hot press firing. The first press treatment and the state in which pressurization is not performed at the time of temperature drop are shown.
In the manner described above, silicon nitride sintered bodies of Comparative Examples 1 and 2 were obtained.

(3-3) Silicon nitride sintered bodies of Comparative Examples 3 and 4 The silicon nitride sintered bodies of Comparative Examples 3 and 4 were different from the silicon nitride sintered bodies of Examples 2 and 4 until drying and granulation. Although it is the same, the subsequent treatment is different from the silicon nitride sintered bodies of Examples 2 and 4. That is, in the silicon nitride sintered bodies of Comparative Examples 3 and 4, the mixed powder was first molded at room temperature and 100 MPa. This molded body was then fired as follows. The molded body was fired (primary firing) in a nitrogen atmosphere at normal pressure, and then HIP fired (fired using a hot isostatic pressing method). During the primary firing, the molded body was held at 1750° C. for 2.5 hours without applying pressure. HIP firing was held at 1650° C. for 2.5 hours under a nitrogen atmosphere of 100 MPa.
In the manner described above, silicon nitride sintered bodies of Comparative Examples 3 and 4 were obtained.
In addition, "normal pressure + HIP" in "firing method" in Table 1 means that primary firing under normal pressure and HIP firing were performed.

2. XRD analysis (X-ray diffraction analysis)
(1) Measurement method Measure the peak intensity I (200) attributed to the crystal plane (200) of β-silicon nitride and/or β-sialon, and the peak intensity (002) attributed to the crystal plane (002). For this purpose, X-ray diffraction measurements were performed on each silicon nitride sintered body. The peak intensities I(200) and I(002) were the peak heights at the following 2θ values.
Peak intensity I (200): Peak height near 2θ = 27.0° Peak intensity I (002): Peak height near 2θ = 64.0° Regarding the outer peripheral surface and end surface of each silicon nitride sintered body, The peak intensities I(200) and I(002) were determined, respectively, and the value of I(200)/(I(200)+I(002)) was calculated. The calculated values on the outer peripheral surface are shown in the "Peak intensity ratio" and "Outer peripheral surface" columns of Table 1. The calculated values at the end face are shown in the columns of “Peak intensity ratio” and “End face” in Table 1.
Note that the peak intensity of each surface was measured under the following conditions.
・X-ray diffraction device RINT-TTR III manufactured by Rigaku Co., Ltd.
・X-ray diffraction conditions Monochromator: used Target: Cu
Tube current: 300mA
Tube voltage: 50kV
Scan speed 2 degrees/min Sampling width 0.02 degrees

(2) Measurement results XRD analysis of the silicon nitride sintered bodies revealed that the outer peripheral surface of the silicon nitride sintered bodies of Examples 1 to 10 was I(200)/(I(200)+I(002) ) was 0.8 or more and 1.0 or less, and I(200)/(I(200)+I(002)) of the end face was 0.5 or more and 0.7 or less.
The silicon nitride sintered bodies of Comparative Examples 1 and 2 are silicon nitride sintered bodies that have not been subjected to the first press treatment in hot press firing. In Comparative Examples 1 and 2, I(200)/(I(200)+I(002)) was less than 0.8 on the outer peripheral surface.
The silicon nitride sintered bodies of Comparative Examples 3 and 4 are silicon nitride sintered bodies that have been subjected to primary firing under normal pressure and HIP firing instead of hot press firing. In the silicon nitride sintered bodies of Comparative Examples 3 and 4, I(200)/(I(200)+I(002)) was less than 0.8 on the outer peripheral surface.

3. Bending strength of silicon nitride sintered body For each test piece of Examples 1 to 10 and Comparative Examples 1 to 4, bending strength at 25°C (MPa) and bending strength at 1000°C (MPa) were determined by the method described in the embodiment. ) was sought. The bending strength (MPa) at 25°C is shown in the columns of "Bending strength" and "25°C: A" in Table 1. The bending strength (MPa) at 1000°C is shown in the columns of "Bending strength" and "1000°C: B" in Table 1.
Then, the ratio (%) of the bending strength at 1000°C to the bending strength at 25°C was calculated. The results are shown in the columns of "Bending strength" and "Strength ratio B/A" in Table 1.

4. Production of End Mill The silicon nitride sintered bodies of Examples 1 to 10 and Comparative Examples 1 to 4 were polished to produce an end mill with a tool shape (outer diameter 10 mm, corner radius 1.25 mm, 4 flutes).
Table 1 shows the composition (mixture) of the raw material powder for the silicon nitride sintered body as described above, but since this composition does not change even after firing, the composition of each silicon nitride sintered body is It is equivalent to the composition. Since each silicon nitride sintered body after firing is machined to form an end mill, the composition of the raw material powder is ultimately the same as the composition of the end mill.

5. Cutting test (1) Test method A cutting test was conducted using each end mill. The test conditions are as follows.
・Work material: FC300
・Cutting speed: 300m/min~
-Evaluation: Increase the cutting speed by 100 m/min and define the speed at which tool breakage occurs as the tool life.

(2) Test results The test results are shown in the "Cutting test" column of Table 1. The end mills of Examples 1 to 10 had high cutting speeds over the tool life and exhibited good fracture resistance. On the other hand, the end mills of Comparative Examples 1 to 4 had lower cutting speeds during tool life and lower fracture resistance than the end mills of Examples 1 to 10.
From the above results, when observed from the outer peripheral surface, the relational expression [1]: 0.80≦I(200)/(I(200)+I(002))≦1.00 is satisfied, and when observed from the end surface It was confirmed that the fracture resistance of the end mill was improved by satisfying relational expression [2]: 0.50≦I(200)/(I(200)+I(002))≦0.70.

6. Production of a friction stir welding tool The silicon nitride sintered bodies of Examples 1 to 10 and Comparative Examples 1 to 4 were polished to form a friction stir welding tool having a tool shape (shoulder diameter 12 mm, probe length 2 mm). Created.
Table 1 shows the composition (mixture) of the raw material powder for the silicon nitride sintered body as described above, but since this composition does not change even after firing, the composition of each silicon nitride sintered body is It is equivalent to the composition. Since each silicon nitride sintered body after firing is machined into a friction stir welding tool, the composition of the raw material powder is ultimately the same as the composition of the friction stir welding tool.

7. FSW (Friction Stir Welding) Test (1) Test Method An FSW test was conducted using each friction stir welding tool. The test conditions are as follows.
・Work material: SUS304
・Tool rotation speed: 1000 rpm
・Joining speed: 100mm/min~
-Evaluation: Increase the welding speed by 50 mm/min, and define the speed at which tool breakage occurs as the tool life.

(2) Test results The test results are shown in the "FSW test" column of Table 1. The friction stir welding tools of Examples 1 to 10 had a high welding speed over the tool life and exhibited good fracture resistance. On the other hand, the friction stir welding tools of Comparative Examples 1 to 4 had lower welding speeds over the tool life and lower fracture resistance than the friction stir welding tools of Examples 1 to 10.
From the above results, when observed from the outer peripheral surface, the relational expression [1]: 0.80≦I(200)/(I(200)+I(002))≦1.00 is satisfied, and when observed from the end surface It has been confirmed that by satisfying the relational expression [2]: 0.50≦I(200)/(I(200)+I(002))≦0.70, the fracture resistance of the friction stir welding tool is improved. Ta.

The present invention is not limited to the embodiments detailed above, and various modifications and changes can be made within the scope of the claims of the present invention.

10...End mill 11...Silicon nitride sintered body 20...End face 21...Bottom blade 22...Corner 30...Outer peripheral surface 31...Outer peripheral blade 32...Chip discharge groove 110...Friction stir welding tool 111...Silicon nitride sintered body 112 ...Shaft part 113...Protrusion part 114, 115...Member to be joined 120...End face 130...Outer peripheral surface WA...Joining area WL...Joining line X1...Axis line X2...Axis line

Claims (6)

An end mill composed of a silicon nitride sintered body containing silicon nitride or sialon as a main component,
The silicon nitride sintered body has an end face and an outer circumferential face continuous with the end face,
The silicon nitride sintered body contains at least one of β silicon nitride and β sialon,
Among the XRD peaks of the silicon nitride sintered body, the peak intensity I (200) attributed to the crystal plane (200) of the β silicon nitride and/or the β sialon, and the peak intensity I (200) of the β silicon nitride and/or The peak intensity I(002) attributed to the crystal plane (002) of the β-sialon satisfies the following relational expression [1] when observed from the outer circumferential surface, and the following when observed from the end face: An end mill that satisfies relational expression [2].

Relational expression [1]: 0.80≦I(200)/(I(200)+I(002))≦1.00
Relational expression [2]: 0.50≦I(200)/(I(200)+I(002))≦0.70
The end mill according to claim 1, wherein the silicon nitride sintered body has a bending strength at 1000°C that is 90% or more of a bending strength at 25°C. The end mill according to claim 1 or 2, wherein a coating layer is formed on the surface. A friction stir welding tool composed of a silicon nitride sintered body containing silicon nitride or sialon as a main component,
The silicon nitride sintered body has an end face and an outer circumferential face continuous with the end face,
The silicon nitride sintered body contains at least one of β silicon nitride and β sialon,
Among the XRD peaks of the silicon nitride sintered body, the peak intensity I (200) attributed to the crystal plane (200) of the β silicon nitride and/or the β sialon, and the peak intensity I (200) of the β silicon nitride and/or The peak intensity I(002) attributed to the crystal plane (002) of the β-sialon satisfies the following relational expression [1] when observed from the outer peripheral surface, and the following when observed from the end face: A friction stir welding tool that satisfies relational expression [2].

Relational expression [1]: 0.80≦I(200)/(I(200)+I(002))≦1.00
Relational expression [2]: 0.50≦I(200)/(I(200)+I(002))≦0.70
The friction stir welding tool according to claim 4, wherein the silicon nitride sintered body has a bending strength at 1000°C that is 90% or more of a bending strength at 25°C. The friction stir welding tool according to claim 4 or 5, wherein a coating layer is formed on the surface.

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