JP6776045B2 - Friction stir welding tool - Google Patents

Description

The present invention relates to a friction stir welding tool.

Conventionally, a tool having a protrusion is rotated and pushed into the object to be joined from the protrusion side, a part of the object to be welded is softened by frictional heat, and the softened part is agitated by the protrusion to join the object to be joined. Friction stir welding is known. It is desired that the friction stir welding tool used for such friction stir welding has more excellent heat resistance, wear resistance, oxidation resistance, and toughness. Therefore, conventionally, it has been proposed to use silicon nitride as a material for forming a friction stir welding tool. Further, in the friction stir welding tool using silicon nitride in this way, for example, in order to further improve the wear resistance, the element selected from B, Al, Ti, and Si together with the first phase made of silicon nitride. A configuration has been proposed in which a second phase composed of a nitride or the like is provided (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2011-98842 International Publication No. 2016/0473776

However, when the second phase is provided as described above, the effect of improving the wear resistance by providing the second phase can be obtained, but the ratio of the first phase is relatively lowered by providing the second phase. As a result, the decrease in strength of the entire friction stir welding tool may decrease. In such a case, as a result, it is difficult to sufficiently improve the durability of the friction stir welding tool. Further, when the second phase is provided, it is necessary to add an additional material for providing the second phase when manufacturing the friction stir welding tool. Further, when the second phase is provided, the manufacturing process may be complicated in order to provide the desired second phase. Therefore, there has been a demand for a technique for improving heat resistance, wear resistance, oxidation resistance, strength, and toughness of a friction stir welding tool without complicating the composition and manufacturing process of the friction stir welding tool.

The present invention has been made to solve the above-mentioned problems, and can be realized as the following forms.

(1) According to one embodiment of the present invention, a friction stir welding tool is provided. The friction stir welding tool includes a sialon phase comprising β-sialon represented by α-sialon and _{Si 6-Z Al Z O Z} N 8-Z, wherein the grain boundary phase, a; Z value of the β sialon, 0.2 ≦ Z ≦ 0.7; at least a part of the grain boundary phase is formed by an oxynitride of a rare earth element and silicon; the oxynitride has a content of β-sialon. up to X-ray intensity ratio are contained in a proportion of 0.15 to 0.75 for; the α indicating the ratio of sialon α ratio of the sialon phase is state, and are 10% to 40%, The friction stir welding tool has a shaft portion extending in the axial direction and a protruding portion provided so as to project in the axial direction from the surface of the end portion of the shaft portion on the side in contact with the object to be joined. At least one of the surface of the end portion and the surface of the protrusion is a burnt surface .
According to this form of a friction stir welding tool, the heat resistance, abrasion resistance, oxidation resistance, strength, and toughness of the friction stir welding tool without complicating the composition and manufacturing process of the friction stir welding tool. It is possible to improve the durability of the friction stir welding tool.

(2) In the friction stir welding tool of the above-described embodiment, the Vickers hardness may be 16 GPa or more. According to this form of the friction stir welding tool, the wear resistance and strength of the friction stir welding tool can be further improved.

(3) In the friction stir welding tool of the above-described embodiment, the shaft portion extending in the axial direction of the friction stir welding tool and the end surface of the shaft portion on the side in contact with the object to be joined protrude in the axial direction. It is also possible that at least one of the surface of the end portion and the surface of the protrusion portion is a burnt surface. According to this form of the friction stir welding tool, the processing process of the friction stir welding tool can be simplified, and the wear resistance of the friction stir welding tool can be further improved.

(4) In the friction stir welding tool of the above-described embodiment, only one of the surface of the end portion and the surface of the protrusion may be a burnt surface. With such a configuration, the wear resistance of the friction stir welding tool can be further improved.

The present invention can also be realized in various forms other than the friction stir welding tool. For example, it can be realized in the form of a friction stir welding device provided with a friction stir welding tool, a method for manufacturing a friction stir welding tool, a friction stir welding method, and the like.

It is a perspective view which shows the whole structure of the friction stir welding tool of embodiment. It is explanatory drawing which illustrated the use state of a tool. It is explanatory drawing which illustrated the use state of a tool. It is explanatory drawing which illustrated the use state of a tool. It is a flowchart which showed an example of the manufacturing method of a tool. It is explanatory drawing which shows the measurement result and the test result which concerns on each sample. It is explanatory drawing which shows the measurement result and the test result which concerns on each sample. It is a figure which shows the result of having analyzed the polished surface and the burnt surface of a sample 19 by an X-ray diffractometer. It is a figure which shows the state which observed the cross section of a ceramic sintered body before processing by SEM. It is a figure which shows the state which observed the cross section of a ceramic sintered body before processing by SEM.

A. Embodiment:
A-1. Tool configuration:
FIG. 1 is a perspective view showing an overall configuration of a friction stir welding tool 10 (hereinafter, also simply referred to as “tool 10”) as an embodiment of the present invention. The tool 10 is made of a ceramic sintered body. The tool 10 includes a shaft portion 11 and a protrusion portion 12. The shaft portion 11 is formed in a substantially columnar shape extending in the X direction of the axis. The protruding portion 12 is formed in a substantially columnar shape, and is provided so as to project in the axis X direction from a surface perpendicular to the axis X at one end of the shaft portion 11. The protrusion 12 is formed at the center of a surface perpendicular to the axis X at one end of the shaft 11, and the axis of the protrusion 12 coincides with the axis X of the shaft 11. At the time of friction stir welding, the tool 10 is used by pressing the protrusion 12 against the object to be welded while making the protrusion 12 in contact with the object to be welded. That is, the one end of the shaft portion 11 is the end on the side that comes into contact with the object to be joined. Of the surface of the tool 10, the surface of the shaft portion 11 at one end thereof that is perpendicular to the axis X is also referred to as a shoulder portion 13.

2A to 2C are explanatory views illustrating a usage state of the tool 10. The tool 10 is used by being attached to a joining device (not shown). When using the tool 10, first, the protrusion 12 is arranged above the stacked objects to be joined (members 21 and 22 to be joined) (see FIG. 2A). Then, in a state where the protrusion 12 is rotated around the axis X, the protrusion 12 of the tool 10 is pushed into the members to be joined 21 and 22 from above while being pressed by the joining device (see FIG. 2B). In this way, by continuing to rotate the protrusion 12 around the axis X while the protrusion 12 is pushed into the members 21 and 22 to be joined, the members 21 and 22 to be joined in the vicinity of the protrusion 12 The region is plastically flowed by frictional heat. A joint region is formed by the protrusion 12 stirring the plastically flowed portions (the portions shown with hatches in FIGS. 2B and 2C) of the members 21 and 22 to be joined (see FIG. 2C). Through this joining region, the members 21 and 22 to be joined are joined to each other. In such a joining step, not only the protrusion 12 but also at least the shoulder portion 13 is in contact with the portion where the composition has flowed. After that, the friction stir welding is completed by pulling out the protrusions 12 from the members 21 and 22 to be joined. In the present embodiment, the members 21 and 22 to be joined are steel plates, but may be any other metal such as aluminum instead of steel.

The tool 10 includes a "sialon phase" and a "grain boundary phase". The "sialon phase" includes α-sialone and β-sialon represented by Si _6-Z Al _Z O _Z N _8-Z . That is, in the tool 10, the crystal grains of α-sialon and the crystal grains of β-sialon are mixed in the sintered body. β-sialon, like silicon nitride (Si 3 _{N 4),} has the property of being high tenacity for forming a needle-like crystal grains entangled tissue. α-sialone has a lower toughness than β-sialon, but has a higher hardness than β-sialon.

The sialone phase may further contain sialone other than α-sialone and β-sialone. Examples of sialons other than α-sialone and β-sialon include 15R-sialon, 21R-sialon, and 12H-sialon.

In the present embodiment, the α rate indicating the ratio of α-sialon in the sialon phase is 10% or more and 40% or less. The α rate is obtained as follows. That is, the α ratio is measured by measuring the peak intensities of the top two peaks (hereinafter, also referred to as the two strongest peaks) having the highest intensities among the peaks of each sialon by an X-ray diffractometer using Cu-Kα rays. Seeking by. Specifically, when the sialone phase contains substantially only α-sialone and β-sialone, the α-rate indicates that the (101) plane peak intensity of β-sialone is β1 and the (210) plane peak intensity of β-sialone is β1. Is β2, the (102) plane peak intensity of α-sialon is α1, and the (210) plane peak intensity of α-sialon is α2, and it is calculated by the following equation (1). When the sialone phase contains sialone other than α-sialone and β-sialone, the peak intensities of the two strongest peaks are measured for each of the other types of sialons and added to the denominator of Eq. (1). By doing so, the α rate may be obtained.

α rate (%) = (α1 + α2) / (β1 + β2 + α1 + α2) × 100… (1)

If the α ratio is less than 10%, the wear resistance of the tool 10 may be insufficient due to the low proportion of α-sialon having high hardness. Further, when the α ratio exceeds 40%, the ratio of β-sialon having high toughness is low, so that the tool 10 becomes brittle and may be damaged during use, resulting in a decrease in durability. For example, the α ratio tends to decrease as the heating temperature in the firing process described later in manufacturing the tool 10 is increased and the heating time in the firing process is increased.

The total ratio of α-sialone and β-sialon in the sialone phase is preferably 80 to 100%. Here, the ratio of each sialon in the sialon phase can be calculated by measuring the peak intensities of the two strongest peaks of each sialon in the same manner as the α ratio described above, which is the ratio of α sialon in the sialon phase. it can. The proportion of α-sialon, β-sialon, and other sialon in the sialon phase can be adjusted, for example, by the ratio of the raw material powder to be blended during the manufacture of the tool 10.

Further, in the present embodiment, in β-sialon contained in the sialon phase, the Z value indicating the degree to which aluminum (Al) and oxygen (O) are dissolved in silicon nitride (Si ₃ N ₄ ) is 0.2 ≦ Z. ≤0.7. Here, sialon, by aluminum and oxygen dissolved in the silicon nitride _(Si 3 _{N 4),} as compared to silicon nitride _(Si 3 _{N 4),} heat resistance, mechanical strength in a high-temperature environment, heat It exhibits properties such as excellent impact resistance and oxidation resistance. Further, when Sialon is used as the ceramic sintered body constituting the tool 10, a chemical reaction with the member to be processed is less likely to occur as compared with the case where silicon nitride (Si ₃ N ₄ ) is used. As described above, as compared with silicon nitride (Si ₃ N ₄ ), the reaction with the member to be processed is less likely to occur and the strength is high, so that Sialon exhibits excellent wear resistance. If the Z value is less than 0.2, the above-mentioned performance as Sialon cannot be sufficiently obtained, and the wear resistance may be lowered. Further, when the Z value exceeds 0.7, the effect of the decrease in strength and the decrease in thermal conductivity in the tool 10 becomes large due to the excessive amount of solid solution of aluminum and oxygen. For example, when the thermal conductivity of β-sialon decreases, the tool 10 becomes overheated and its durability decreases, or the durability of the tool 10 decreases due to a large difference in the coefficient of thermal expansion in the tool 10. there's a possibility that. Further, when the amount of the solid solution becomes excessive, the crystal grains of β-sialon become brittle, and the strength of the entire sintered body may decrease.

Here, for the Z value of β-sialon, the a-axis lattice constant of β-sialon inside about 1 mm or more from the burnt surface of the ceramic sintered body is obtained by X-ray diffraction, and the a-axis lattice constant of β-silicon nitride (7). It is a value calculated by the difference from .60442Å). The calculation method is based on the following formula (2). In the equation, a represents the a-axis lattice constant of the measured β-sialon. It should be noted that the burnt surface is different from the machined surface which is subjected to processing such as grinding or polishing after obtaining a ceramic sintered body by the firing process described later in the manufacturing process of the tool 10, and is subjected to such processing. Not a raw surface.

Z = (a-7.60442Å) /0.03 ... (2)

The Z value of β-sialon can be adjusted, for example, by the type and amount of the sintering aid described later used for manufacturing the tool 10. For example, the higher the proportion of the sintering aid, the larger the Z value tends to be.

It is desirable that each crystal particle of β-sialon constituting the sialon phase has a major axis length of 10 μm or less and a minor axis length of 1.2 μm or less. Here, the length of the long axis of β-sialon refers to the length of the portion having the largest width in the β-sialon particles. The length of the minor axis of β-sialon refers to the length of the smallest portion of the width in the direction orthogonal to the major axis of the β-sialon particles. By setting the size of the β-sialon particles as described above, it is possible to suppress a decrease in the strength of the tool 10 due to the excessive particles. In order to ensure the characteristic that β-sialone has high toughness by forming a structure in which needle-shaped crystal grains are entangled, the major axis of each particle of β-sialon must be 0.1 μm or more. Is desirable.

The "grain boundary phase" refers to a portion where a boundary between crystal grains appears. The grain boundary phase is a part that looks like a mesh when the structure is observed with an optical microscope. In this embodiment, at least a part of this grain boundary phase is formed by an oxynitride of a rare earth element and silicon. The oxynitride of a rare earth element and silicon can be indicated as ReSiO ₂ N or Re ₂ Si ₃ O ₃ N ₄ (where Re is a rare earth element). The type of oxynitride present in the grain boundary phase depends on the composition of the sintering aid, which will be described later, used when manufacturing the tool 10. As the oxynitride present in the grain boundary phase, Re ₂ Si ₃ O ₃ N ₄ is more preferable. Here, the rare earth element is a general term for scandium (Sc), yttrium (Y), and lanthanoid. Examples of the lanthanoid include europium (Eu), dysprosium (Dy), ytterbium (Yb), lutetium (Lu), lanthanum (La), cerium (Ce), and praseodymium (Pr). Examples of the oxynitride of the rare earth element and silicon include YSiO ₂ N, Y ₂ Si ₃ O ₃ N ₄ , YbSiO ₂ N, Yb ₂ Si ₃ O ₃ N ₄ , DySiO ₂ N, Dy ₂ Si ₃ O ₃ Examples thereof include N ₄ , ErSiO ₂ N, Er ₂ Si ₃ O ₃ N ₄ , LuSiO ₂ N, Lu ₂ Si ₃ O ₃ N ₄ . As the rare earth element, for example, yttrium (Y) is desirable, and as the oxynitride of the rare earth element and silicon, for example, YSiO ₂ N and Y ₂ Si ₃ O ₃ N ₄ are desirable, and Y ₂ Si ₃ O ₃ N ₄ is particularly desirable.

In the tool 10 of the present embodiment, at least a part of the grain boundary phase is formed of an oxynitride of a rare earth element and silicon, thereby improving the oxidation resistance of the ceramic sintered body constituting the tool 10. be able to. As a result, the wear resistance of the tool 10 can be improved.

In the tool 10 of the present embodiment, the oxynitride of the rare earth element and silicon is contained at a ratio of 0.15 or more and 0.75 or less in the maximum X-ray intensity ratio with respect to the content of β-sialon. The maximum X-ray intensity ratio R representing the content of the above-mentioned oxynitride with respect to β-sialon is calculated by the following equation (3).

Maximum X-ray intensity ratio R = P1 / P2 ... (3)
(In the formula, P1 is a peak measured by an X-ray diffractometer using Cu-Kα rays, and is the intensity of the peak showing the highest intensity among the peaks showing oxynitrides of rare earth elements and silicon. P2 is a peak measured by an X-ray diffractometer, and represents the intensity of the peak showing the highest intensity among the peaks showing β-sialon.)

When the maximum X-ray intensity ratio R is less than 0.15, the glass phase having low high temperature characteristics (for example, heat resistance and oxidation resistance) and mechanical characteristics (for example, strength) at the grain boundaries of the ceramic sintered body The proportion may increase. Therefore, by setting the maximum X-ray intensity ratio R to 0.15 or more, the chemical stability and strength of the tool 10 can be improved, and the wear resistance can be improved. On the other hand, when the maximum X-ray intensity ratio R of the oxynitride to β-sialon exceeds 0.75, the proportion of different phases in the ceramic sintered body constituting the tool 10 increases, and the strength of the tool 10 due to the different phases increases. A drop can be caused. Therefore, by setting the maximum X-ray intensity ratio R to 0.15 or more and 0.75 or less, it is possible to achieve both improvement in wear resistance and improvement in strength in the tool 10.

When a plurality of types of oxynitrides are present as oxynitrides of a rare earth element and silicon, the sums of the intensities of the peaks showing the highest intensities in each oxynitride are summed up and the above-mentioned maximum X-ray The strength ratio R may be obtained. Specifically, for example, when yttrium (Y) is used as a rare earth element and both Y ₂ Si ₃ O ₃ N ₄ and YSiO ₂ N are present as oxynitrides, Y ₂ Si ₃ O ₃ N ₄ of the sum of the maximum intensity of the highest intensity and YSiO ₂ N, as P1 in previously described (3), may be obtained up to the X-ray intensity ratio R.

The maximum X-ray intensity ratio R, which represents the content of the oxynitride with respect to the content of β-sialon, is, for example, to raise the heat treatment temperature or lengthen the heat treatment time in the firing treatment described later during the manufacture of the tool 10. As a result, it tends to increase. On the other hand, the maximum X-ray intensity ratio R tends to be reduced by lowering the heat treatment temperature or shortening the heat treatment time. The maximum X-ray intensity ratio R is more preferably 0.3 or more from the viewpoint of further improving the durability of the tool 10.

It is desirable that the oxynitride of the rare earth element and silicon exists in the grain boundary phase as finely dispersed as possible. Specifically, for example, it is desirable that the oxynitride is dispersed in the grain boundary phase in a state where the maximum particle size of the oxynitride is 5 μm or less. As described above, when the oxynitride is dispersed in the grain boundary phase in a state where the particle size is fine, the above effect due to the presence of the oxynitride in the grain boundary phase can be easily obtained. On the other hand, when the particle size of the oxynitride is excessive, the influence of the presence of foreign matter at the grain boundaries becomes large, and the strength of the entire ceramic sintered body, that is, the tool 10 may decrease. There is sex. The particle size of the oxynitride in the grain boundary phase refers to the average particle size obtained by the line intercept method. In the line intercept method, a plurality of straight lines are drawn in parallel on the observation image, and the average value of the lengths of the straight lines crossing the particles (the portion observed as the aggregate of the oxynitride) is calculated. It is a known method of obtaining the average particle size. The observation screen can be, for example, a field of view in which an arbitrary cross section of the tool 10 is observed at a magnification of 5000 times. Further, the number of straight lines drawn when determining the average particle size can be, for example, 10.

Further, it is desirable that the tool 10 of the present embodiment has a Vickers hardness of 16 GPa or more. As a result, the wear resistance and strength of the tool 10 can be further improved. In the present specification, Vickers hardness refers to a value measured at room temperature (25 ° C.) according to the measuring method specified in JIS R1610. The test load at the time of measuring the Vickers hardness is 10 kgf. The Vickers hardness of the tool 10 tends to increase as the α ratio of the tool 10 increases. Further, the Vickers hardness of the tool 10 tends to increase as the maximum X-ray intensity ratio R of the tool 10 described above becomes smaller. However, the Vickers hardness of the tool 10 can be less than 16 GPa.

The tool 10 may further have a coating layer on the surface of the ceramic sintered body described above. By providing the coating layer, the wear resistance of the tool 10 can be further improved. The coating layer may be constructed using a substance that has sufficient heat resistance to form a friction stir welding tool and does not cause an undesired reaction with the ceramic sintered body. As a method for forming the coating layer, for example, CVD or PVD can be adopted.

A-2. Tool manufacturing method:
FIG. 3 is a flowchart showing an example of a method for manufacturing the tool 10. Various materials and numerical values (for example, average particle size of powder, mixing time, heating time, heating temperature, etc.) used in the following description are examples thereof, and values other than these are arbitrarily adopted. be able to.

When manufacturing the tool 10, first, the raw material powder for obtaining the ceramic sintered body is weighed (step S110). Specifically, the raw material powder comprises mainly a silicon nitride (Si 3 _{N 4)} powder as a raw material, a sintering aid, and in the ceramic sintered body obtained, alpha sialon and β-sialon, and rare earth It is composed of a compound that forms an oxynitride of element and silicon. The sintering aid contains at least an aluminum compound and a compound containing a rare earth element.

The aluminum compound preferably contains at least one of aluminum oxide (Al ₂ O ₃ ) and aluminum nitride (Al N). By using such an aluminum compound, silicon nitride can be made into sialon by dissolving aluminum and oxygen in silicon nitride. As the compound containing a rare earth element, for example, the above-mentioned oxide of a rare earth element can be used. When aluminum nitride (AlN) is used together with such an oxide of a rare earth element, the acid nitride of the rare earth element can be easily formed in the obtained ceramic sintered body.

After step S110, the weighed raw material powder is mixed and pulverized to prepare a slurry (step S120). Mixing and grinding can be performed, for example, by mixing the raw material powder with a solvent (eg, ethanol) using a ball mill. The crushing time is not particularly limited, but for example, 20 hours to 30 hours can be exemplified. As a result, a slurry containing the raw material powder can be obtained. Then, the obtained slurry is boiled and dried to remove ethanol, whereby a mixed powder can be obtained (step S130).

After the step 130, the obtained mixed powder is press-molded and fired to obtain a ceramic sintered body (step S140). The shape of the molded product obtained by press molding is not particularly limited, but may be, for example, substantially cylindrical. In step S140, after press molding of the mixed powder, a cold isotropic pressure treatment (CIP treatment) may be further performed to obtain a molded product. The firing treatment can include primary firing, hot isotropic pressure pressing treatment (HIP treatment), and heat treatment for forming grain boundary phases. The firing temperature at the time of primary firing is preferably 1550 to 1950 ° C., and the firing time is preferably 1 to 3 hours. The firing temperature of the HIP treatment is preferably 1500 to 1800 ° C., the firing time is 1 to 3 hours, the gas pressure is 10 to 200 MPa, and the firing time is preferably N ₂ atmosphere. The heating temperature of the heat treatment is 1,300-1,750 ° C., 1 to 3 hours heating time is preferably carried out under _{N 2} atmosphere. After the step S140, the tool 10 is completed by processing the obtained ceramic sintered body into a tool shape (for example, cutting, grinding, polishing, etc.) (step S150).

According to the tool 10 of the present embodiment configured as described above, Sialon is excellent in heat resistance and toughness without complicating the composition and manufacturing process of the tool by providing a special phase in the tool 10. It is possible to make a tool having better oxidation resistance and strength (hardness) while retaining its characteristics. That is, the wear resistance of the tool 10 can be improved by increasing the oxidation resistance and suppressing the chemical reaction with the object to be joined. Further, by increasing the strength (hardness) of the tool 10, it is possible to prevent the tool 10 from being damaged during friction stir welding. As a result, the durability of the tool 10 can be improved (the life of the tool 10 can be extended). Such a tool 10 can be particularly preferably used when a steel object to be joined, which has a higher softening temperature than aluminum or the like, is used.

B. Modification example:
In the above embodiment, the tool 10 is formed into a substantially columnar shape in step S140 at the time of manufacturing, and is processed into a tool shape having a protrusion 12 by processing in step S150, but a different configuration may be used. For example, in step S140, the tool 10 may be formed into a tool shape, and in step S150, the tool 10 may be manufactured without processing at least a part of the surface of the molded body.

Specifically, on the surface of the tool 10, at least one of the surface of the protrusion 12 and the surface of the shoulder portion 13 may be a burnt surface. By doing so, the processing step in step S150 can be simplified. Further, the wear resistance of the tool 10 can be further improved. In particular, when only one of the surface of the protrusion 12 and the surface of the shoulder portion 13 is the burnt surface, the wear resistance of the tool 10 can be further improved. The above-mentioned effect of improving the wear resistance of the tool 10 is that at least one of the surface of the protrusion 12 and the surface of the shoulder portion 13 is a burnt surface, so that the fluidity of the object to be softened during friction stir welding Is presumed to be obtained by being affected. It should be noted that at least one of the surface of the protrusion 12 and the surface of the shoulder portion 13 is a burnt surface, that is, at least a part of at least one of the surface of the protrusion 12 and the surface of the shoulder portion 13 is a burnt surface. Including the case where the skin is burnt.

Tools of Samples 1 to 26 were prepared as various tools having different α ratio, Z value, maximum X-ray intensity ratio R, Vickers hardness, and the like. Then, a joining test was performed on each sample to evaluate the performance as a tool. 4 and 5 are explanatory views showing measurement results and test results for each sample.

[Manufacturing of sintered body and tools]
The tools of Samples 1 to 26 were prepared by the method described with reference to FIG. More specifically, in any of the samples, in step S110, the main raw material average particle diameter 0.1μm of silicon nitride _(Si 3 _{N 4)} powder and the average particle diameter 1.0μm or less sintering aids Powder was used. Sample 1～13,18～26, as sintering aid powder, using yttrium oxide _(Y 2 _{O 3)} powder, aluminum oxide _(Al 2 _{O 3)} powder, and aluminum nitride (AlN) powder. In these samples 1 to 13 and 18 to 26, the blending ratio of the silicon nitride (Si ₃ N ₄ ) powder and each sintering aid powder, and the heating temperature and heating time in the firing treatment were different, respectively. Further, instead of the yttrium oxide (Y ₂ O ₃ ) in the sintering aid powder, europium oxide (Eu ₂ O ₃ ) was used in sample 14, and dysprosium oxide (Dy ₂ O ₃ ) was used in sample 15. In sample 16, ytterbium oxide (Yb ₂ O ₃ ) was used, and in sample 17, lutetium oxide (Lu ₂ O ₃ ) was used.

After blending the raw material powder, the blended raw material powder and ethanol were placed in a resin pot and mixed and pulverized for 24 hours to obtain a slurry (step S120). Then, the slurry was boiled and dried to remove ethanol to prepare a mixed powder (step S130). After press molding the obtained powder, a cold isotropic pressure treatment (CIP treatment) was performed to prepare a molded product.

Then, after performing primary firing (1700 ° C. to 1800 ° C., 2 hours) in a nitrogen atmosphere of 0.1 MPa to 0.9 MPa, hot isotropic pressure pressurization treatment (HIP treatment) (HIP treatment) in a nitrogen atmosphere of 100 MPa. 1650 ° C. to 1750 ° C. for 2 hours) to prepare a sintered body. Then, heat treatment (1500 ° C. to 1700 ° C., 2 hours) was performed in a nitrogen atmosphere (step S140). By this heat treatment, a grain boundary _{phase, Y 2 Si 3 O 3 N} 4 phase is generated.

In Samples 1 to 17 and 21 to 26, the sintered body was formed into a substantially cylindrical shape in step S140, and the prepared sintered body was processed in step S150 to prepare a tool having a shoulder portion 13 and a protrusion portion 12 (). Step S150).

In Samples 18 to 20, in step 140, the shape is formed to have the shoulder portion 13 and the protrusion 12, and in step 150, at least one surface of the shoulder portion 13 and the protrusion 12 is not processed. .. Specifically, in the sample 18, the entire surface of both the shoulder portion 13 and the protrusion portion 12 was used as a burnt surface. In sample 19, only the entire surface of the shoulder portion 13 was used as the burnt surface. In the sample 20, only the entire surface of the protrusion 12 was used as the burnt surface. Samples 18 to 20 were prepared under the same conditions except for the conditions relating to the presence or absence of processing on the surface.

In order to reduce the Vickers hardness of the sample 21, the heat treatment temperature was set to 1800 ° C., which is higher than that of the other samples.

In Samples 22 to 26, a coating layer was further provided on the surface of the ceramic sintered body processed in step S150. Specifically, sample 22 uses the ceramic sintered body of sample 1 as a base material, samples 23, 25, and 26 use the ceramic sintered body of sample 3 as a base material, and sample 24 uses the ceramic sintered body of sample 3 as a base material. A ceramic sintered body was used as a base material. Samples 22 to 25 formed a coating layer on these substrates by a CVD (chemical vapor deposition) method, and sample 26 formed a coating layer by a PVD (physical vapor deposition) method. In the samples 22 to 25 using the CVD method, aluminum nitride (α-AlON), titanium carbide (TiC), titanium carbide (TiCN), and titanium nitride (TiN) were used as film forming materials. Here, in the samples 22 to 24, the film thickness was 1.5 μm, and in the sample 25, the film thickness was 3.0 μm. In the sample 26 using the PVD method, titanium nitride aluminum (TiAlN) was used as the film forming material, and the film thickness was 1.5 μm.

The number of each sample used in the test was set to 1. Further, in the shape of each sample, the diameter of the shaft portion 11 is 12 mm, the diameter of the protrusion 12 is 4 mm, the length of the shaft portion 11 along the axis X is 18.5 mm, and the length of the protrusion 12 is 1.5 mm. And said.

[Measurement of physical properties of each sample]
For each of the prepared samples, the α ratio, the Z value, and the maximum X-ray intensity ratio R were derived, and the Vickers hardness was measured. These derivation methods and measurement methods were the same as those in the above-described embodiment.

[Joining test]
A joining test was performed on each of the prepared samples. As shown in FIG. 2, steel plates as members to be joined were stacked, and point joining was performed by pressing a tool against these steel plates. The joining test was carried out under the conditions shown below.

<Test conditions>
-Member to be joined: SUS304 (thickness 2 mm)
・ Shield gas: Argon (Ar)
・ Descent speed: 0.5 mm / s
・ Tool pushing load: 1.2 × 10 ³ kgf
・ Rotation speed: 600 rpm
・ Retention time: 1 sec
・ RBI: 60

Here, the "shield gas" refers to a gas arranged in the test space in order to break the contact between the member to be joined and the air during the test. The "descent speed" indicates the speed at which the tool 10 is brought close to the member to be joined. The “tool pushing load” indicates the pushing load of the tool 10 against the member to be joined. “Rotation speed” indicates the rotation speed of the tool 10. The “holding time” indicates the time during which the member to be joined is held in a state where the pushing load from the tool 10 is applied. “RBI” indicates the number of repetitions of this test.

<Evaluation method>
The tool condition after the test was evaluated. The tool state was evaluated by measuring the lengths of the protrusions 12 and the shoulders 13 along the axis X before and after the test. The judgment criteria are shown below. As for the judgment, ◎ has the highest evaluation, and the evaluation decreases in the order of ○, △, and ×.
X: (i) The amount of wear of the shoulder portion 13 is 0.5 mm or more and the amount of wear of the protrusion 12 is 0.4 mm or more, whichever is satisfied, or (ii) the sample is damaged (damage such as chipping). ).
-Δ: Among the samples that do not satisfy "x", the wear amount of the shoulder portion 13 is 0.3 mm or more and less than 0.5 mm, and the wear amount of the protrusion 12 is 0.2 mm or more and less than 0.4 mm. Satisfy at least one of the above.
-○: Among the samples not satisfying "Δ", the wear amount of the shoulder portion 13 is larger than 0.2 mm and less than 0.3 mm, and the wear amount of the protrusion 12 is larger than 0.05 mm and less than 0.2 mm. Satisfy at least one of them.
-⊚: The amount of wear of the shoulder portion 13 is 0.2 mm or less, and the amount of wear of the protrusion 12 is 0.05 mm or less.

[Evaluation results]
In FIGS. 4 and 5, those satisfying the following requirements are shown as examples, and those not satisfying the following requirements are shown as comparative examples.
(I) The α rate is 10% or more and 40% or less.
(II) The Z value satisfies 0.2 ≦ Z ≦ 0.7.
(III) The oxynitride of the rare earth element and silicon shall be contained at a ratio of 0.15 or more and 0.75 or less in the maximum X-ray intensity ratio R with respect to the content of β-sialon.

As shown in FIGS. 4 and 5, Samples 2 to 4, 7, 8, 11, 12, 14 to 21, 23, 25, and 26 satisfy the above requirements (I) to (III) as examples. There is. Samples 1, 5, 6, 9, 10, 13, 22, and 24 are used as comparative examples because they do not satisfy any of the above requirements (I) to (III). Specifically, samples 1, 5, 22 and 24 do not meet requirement (III), samples 6 and 9 do not meet requirement (II), and samples 10 and 13 do not meet requirement (I).

Each sample of the above-mentioned example was evaluated as "⊚" to "Δ" in the joining test. On the other hand, each sample of the comparative example was evaluated as "x" in the joining test. That is, it was confirmed that the strength and wear resistance of the tool are improved by satisfying the requirements (I) to (III).

Of the samples 1 to 5 in which the maximum X-ray intensity ratio was changed, the sample 1 in which the maximum X-ray intensity ratio R was lower than the lower limit of the requirement (III) was evaluated as "x" due to the large amount of wear. ((I) of the evaluation criteria of "x"). On the other hand, in sample 5 in which the maximum X-ray intensity ratio R exceeds the upper limit of the requirement (III), the evaluation was "x" due to the lack of the tool ((ii) of the evaluation standard of "x". )).

Further, among the samples 6 to 9 in which the Z value was changed, the sample 6 in which the Z value was lower than the lower limit of the requirement (II) was evaluated as “x” due to the large amount of wear (“x”). (I) of the evaluation criteria. On the other hand, in the sample 9 in which the Z value exceeds the upper limit value of the requirement (II), the evaluation was "x" due to the lack of the tool ((ii) of the evaluation standard of "x").

Further, among the samples 10 to 13 in which the α rate was changed, the sample 10 in which the α rate was lower than the lower limit of the requirement (I) was evaluated as “x” due to the large amount of wear (“x”). (I) of the evaluation criteria. On the other hand, in the sample 13 in which the α ratio exceeds the upper limit of the requirement (I), the evaluation was “x” due to the lack of the tool ((ii) of the evaluation standard of “x”).

From the results of Samples 14 to 17, if the requirements (I) to (III) are satisfied, the same effect can be obtained even if the rare earth element constituting the oxynitride existing in the grain boundary phase is an element other than yttrium. I was able to confirm that.

From the results of Samples 18 to 20, it was confirmed that it is effective to use at least one of the surface of the shoulder portion 13 and the surface of the protrusion 12 as the burnt surface. In particular, from the results of Samples 19 and 20, the wear resistance and strength of the tool can be further improved by using only one of the surface of the shoulder portion 13 and the surface of the protrusion 12 as the burnt surface. Was confirmed.

FIG. 6 shows the results of analysis of the surface of the protrusion 12 which is the processed surface (polished surface) and the surface of the shoulder portion 13 which is the non-processed surface (burnt surface) of the sample 19 by an X-ray diffractometer. It is a figure which shows. Comparing the polished surface and the burnt surface, it can be seen that only the peaks of Y ₂ Si ₃ O ₃ N ₄ , which are nitrides of rare earth elements and silicon, are significantly reduced by processing.

Further, FIGS. 7A and 7B show a state in which a region including the surface in the cross section before processing of the ceramic sintered body produced in the same manner as in Sample 3 was observed using a scanning electron microscope (SEM). It is a figure. FIG. 7A shows the result of observation at 2000 times, and FIG. 7B shows the result of observation at 5000 times. In FIGS. 7A and 7B, the portion of Y ₂ Si ₃ O ₃ N ₄ is shown in whiter. As can be seen from FIGS. 7A and 7B, the content of Y ₂ Si ₃ O ₃ N ₄ is extremely high in the region near the surface (for example, 10 to 20 μm from the surface), which is the burnt surface. Such a region is a region that is usually removed when performing processing such as grinding or polishing. In addition, in the vicinity of the surface of the burnt surface, the content of Y ₂ Si ₃ O ₃ N ₄ , which is an acid nitride of rare earth elements and silicon, is higher than that in the vicinity of the surface of the processed surface, in the samples 18 to 20. It can be understood from the fact that the burnt surface has a larger maximum X-ray intensity ratio R than the polished surface.

As described above, in the ceramic sintered body having the sialon phase and the grain boundary phase, when at least a part of the grain boundary phase is formed by the oxynitride of the rare earth element and silicon, after the firing treatment. It can be seen that in the ceramic sintered body, more Y ₂ Si ₃ O ₃ N ₄ is present in the vicinity of the surface. Then, in the friction stir welding tool, at least one of the surface of the shoulder portion 13 and the surface of the protrusion 12 is a burnt surface, and preferably only one of the surface of the shoulder portion 13 and the surface of the protrusion 12 is used. It can be seen that the strength and abrasion resistance of the tool can be improved by using a burnt surface.

From the results of Sample 21, it was confirmed that when the Vickers hardness of the tool was less than 16 GPa, the wear resistance and strength of the tool were relatively suppressed. Therefore, in addition to satisfying the requirements (I) to (III), it is desirable that the Vickers hardness of the tool is 16 GPa or more.

From the results of Samples 22 to 26, when a coat layer is provided on the surface of the tool 10, the wear resistance and strength of the tool shown as a result of the joining test are superior or inferior to those without the coat layer (requirements). It was confirmed that the durability of the tool is further improved by satisfying (I) to (III)), and the overall shift is in the direction of improving the wear resistance and strength.

The present invention is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations within a range not deviating from the gist thereof. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in each embodiment described in the column of the outline of the invention may be used to solve some or all of the above-mentioned problems. , It is possible to replace or combine as appropriate in order to achieve a part or all of the above-mentioned effects. Further, if the technical feature is not described as essential in the present specification, it can be appropriately deleted.

10 ... Friction stir welding tool 11 ... Shaft part 12 ... Protrusion part 13 ... Shoulder part 21 and 22 ... Member to be joined

Claims (3)

Friction stir welding tool
includes a sialon phase, and a grain boundary phase, the containing β-sialon represented by α-sialon and _{Si 6-Z Al Z O Z} N 8-Z,
The Z value of β-sialon is 0.2 ≦ Z ≦ 0.7.
At least a part of the grain boundary phase is formed by an oxynitride of a rare earth element and silicon.
The oxynitride is contained in a ratio of 0.15 or more and 0.75 or less in the maximum X-ray intensity ratio with respect to the content of β-sialon.
Wherein α indicates the proportion of a sialon α ratio of the sialon phase is state, and are 10% to 40%,
It has a shaft portion extending in the axial direction of the friction stir welding tool, and a protruding portion provided so as to project in the axial direction from the surface of the end portion of the shaft portion on the side in contact with the object to be joined.
A friction stir welding tool characterized in that at least one of the surface of the end portion and the surface of the protrusion is a burnt surface . The friction stir welding tool according to claim 1.
A friction stir welding tool characterized by a Vickers hardness of 16 GPa or more. The friction stir welding tool according to claim 1 or 2 .
A friction stir welding tool characterized in that only one of the end surface and the surface of the protrusion is a burnt surface.