JP5273529B2 - Manufacturing method of ceramic products, ceramic products - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of increasing flexural strength and contact strength of ceramics. <P>SOLUTION: A method of producing a ceramic product is characterized in that compressive residual stress is introduced into a ceramic sintered body 1 containing 10-30 wt.% of SiC particulates 12 or a ceramic sintered body made from SiC by shot peening treatment, and a crack 2 is formed in the ceramic sintered body 1; and then a heat treatment step is performed, in which SiC is oxidized to produce SiO<SB>2</SB>by heat treatment at a temperature lower than the heating temperature that can remove all the compressive residual stress introduced in the shot peening treatment, under an oxygen-containing atmosphere. Also disclosed is a ceramic product 5 produced by the method. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for manufacturing a ceramic product and a ceramic product capable of improving the strength of the ceramic product.

Since ceramics are brittle materials, there is a problem that reliability during use is inferior to metal materials. In order to solve this problem, a method for toughening ceramics by fiber reinforcement or structure control, or a method for toughening ceramic product surfaces by shot peening in which fine particles are projected onto the ceramic product surface as in Patent Document 1, for example. (Hereinafter also referred to as a peening method) is known.
Further, as in Patent Document 2, the fracture toughness and strength are increased by sintering a material obtained by mixing fine SiC (silicon carbide) particles with ceramic raw material powder (specifically, mullite), and further obtained. There has also been proposed a technique capable of increasing the bending strength by a heat treatment in which the sintered body is heated to a temperature of 1200 ° C. or higher (hereinafter also referred to as a carbide composite method).
Among these, the peening method described above is a technique for surface toughening by shot peening treatment of ceramic products after production, and the carbide composite method is intended to improve bending strength by heat treatment after sintering of ceramic products. All have the process of processing the ceramic product after sintering.
JP 2004-136372 A Japanese Patent Laid-Open No. 7-138067

Since ceramics have extremely low fracture toughness values, when surface defects (cracks) exist, their strength is strongly influenced by the presence of cracks. For example, for ceramic products used as bearings, parts for heat engines such as gas turbines, and structural materials such as springs, it is important to ensure mechanical reliability. On the other hand, machining such as drilling is important. In order to ensure mechanical reliability, it is important to cancel or suppress the influence of cracks formed in ceramics on the strength of the ceramics during machining. Moreover, in order to ensure the mechanical reliability of ceramic products, it is also important to suppress the occurrence of cracks during use as a structural material.
However, canceling (or suppressing) the effects of cracks formed by machining, etc., and suppressing cracks during use are both compatible and practically sufficient (improvement of mechanical reliability). It was not easy and there was no appropriate technology that could realize this.

  The above-described peening method is effective for toughening the surface (surface layer) of ceramics (ceramic products). Improvement of the fracture toughness value of the surface of ceramic products is effective in suppressing crack initiation and crack propagation. However, there is a limit to the depth of introduction of compressive residual stress into ceramics by shot peening treatment (generally about 40 to 50 μm from the surface). Even if the surface is toughened by peening, the surface of the ceramic The fracture toughness values other than are in a very low situation. For this reason, if there are cracks with a depth of, for example, about 50 to 100 μm in the ceramic surface layer, even if the surface is toughened by applying shot peening treatment, this will sufficiently contribute to the improvement of the ceramic strength (bending strength) However, there was dissatisfaction that the strength improvement effect was small.

In the technique described in Patent Document 2, it is considered that carbide particles (SiC) added to mullite generate SiO ₂ by heat treatment, and this SiO ₂ joins and heals the cracks present in the ceramic. It can be said to self-repair cracks. According to this technique, since surface defects (cracks) of the ceramic product can be removed by heat treatment, an improvement in bending strength can be realized. Although this technique can increase the fracture toughness of ceramics by adding carbide particles, however, there is a limit to the improvement of the fracture toughness value, and it is not easy to obtain a high fracture toughness value. Although the improvement in fracture toughness value on the ceramic surface contributes effectively to the suppression of crack generation and propagation on the ceramic surface, the technology described in Patent Document 2 sufficiently provides the effect of suppressing crack generation and propagation in the product after heat treatment. After all, mechanical reliability cannot be satisfied.

  In view of the above problems, the present invention can achieve both cancellation (or suppression) of the influence of cracks formed on the surface of a ceramic product and suppression of occurrence of cracks during use, and mechanical reliability of the ceramic product. The purpose is to provide a ceramic product manufacturing method and ceramic product that can be easily improved.

In order to solve the above problems, the present invention provides the following configuration.
According to a first aspect of the present invention, a surface of the ceramic sintered body is introduced by introducing a compressive residual stress to the ceramic sintered body made of a Si ₃ N ₄ / SiC composite containing 10 to ₃₀ wt% of SiC fine particles by shot peening. After forming a compressive residual stress introduction layer in which a compressive residual stress is introduced in the range of 800 to 1000 MPa in the surface layer portion in the range of 30 to 50 μm in the depth direction, and forming a crack in the ceramic sintered body The ceramic sintered body is heated in an oxygen-containing atmosphere to a temperature of 1100 ° C. or lower and 800 ° C. or higher, which is lower than the heating temperature at which all the compressive residual stress introduced by the shot peening treatment can be removed. The SiC in the compact is oxidized to produce SiO ₂ and the compression residue in the surface layer portion of the ceramic sintered body. There is provided a method for producing a ceramic product, characterized in that a heat treatment step is performed in which a compressive residual stress of 250 MPa or more remains in a residual stress introduction layer.
The second invention is a Si ₃ N ₄ / SiC composite material containing 10 to ₃₀ wt% of SiC fine particles, and the compression residual stress is introduced into the ceramic sintered body having a crack on the surface by shot peening treatment, After forming a compressive residual stress introduction layer having a compressive residual stress introduced in the range of 800 to 1000 MPa on the surface layer portion in the range of 30 to 50 μm in the depth direction from the surface of the ceramic sintered body, the ceramic sintered body Is heated to a temperature of 1100 ° C. or lower and 800 ° C. or higher, which is lower than the heating temperature at which all of the compressive residual stress introduced by the shot peening treatment can be removed in an oxygen-containing atmosphere, and SiC in the ceramic sintered body is Oxidized to generate SiO ₂ and 250 MPa or more in the compressive residual stress introduction layer in the surface layer portion of the ceramic sintered body A method for producing a ceramic product, characterized by performing a heat treatment step for leaving a residual compressive residual stress.
According to a third aspect of the present invention, a surface of the ceramic sintered body is introduced by introducing compressive residual stress to the ceramic sintered body made of a Si ₃ N ₄ / SiC composite containing 10 to ₃₀ wt% of SiC fine particles by shot peening treatment. To the surface layer in the range of 30 to 50 μm in the depth direction, a compressive residual stress introduction layer introduced in a range of 800 to 1000 MPa of compressive residual stress is formed, and the ceramic sintered body after completion of the shot peening treatment After forming cracks on the surface of the ceramic, the ceramic sintered body is at a temperature of 1100 ° C. or lower and 800 ° C. or higher, which is lower than the heating temperature that can remove all the compressive residual stress introduced by the shot peening treatment in an oxygen-containing atmosphere. To oxidize SiC in the ceramic sintered body to produce SiO ₂ , There is provided a method for producing a ceramic product, characterized by performing a heat treatment step for leaving a compressive residual stress of 250 MPa or more in a compressive residual stress introduction layer in a surface layer portion of a sintered body.
In a fourth aspect of the invention, the ceramic sintered body is machined before the heat treatment step, and the heat treatment step is performed after the shot peening treatment and the machining are completed. A method for producing a ceramic product of any of the inventions is provided.
According to a fifth aspect of the present invention, the shot peening treatment is performed using a fine particle projection material having a Vickers hardness (HV) of 50 to 80% of the hardness of the ceramic sintered body and a particle size of 100 to 400 μm at a shot pressure of 0.1 to 0.3 MPa. The method for producing a ceramic product according to any one of the first to fourth aspects of the invention is characterized by projecting onto the ceramic material.
A sixth invention provides the method for producing a ceramic product according to any one of the first to fifth inventions, wherein a particle diameter of the fine particle projection material used in the shot peening treatment is 100 to 200 μm.
A seventh invention is the invention according to any one of the first to sixth inventions, wherein the shot pressure for projecting the fine particle projection material onto the ceramic sintered body in the shot peening treatment is 0.1 to 0.2 MPa. A method for producing a ceramic product is provided.
An eighth invention provides the method for producing a ceramic product according to any one of the first to seventh inventions, wherein the heat treatment step is performed in the atmosphere.
A ninth invention provides the method for producing a ceramic product according to any one of the first to eighth inventions, wherein the heat treatment step is performed in a state in which a bending stress is applied to the ceramic sintered body.
A tenth aspect of the invention is a ceramic product manufactured by the method for manufacturing a ceramic product according to any one of the first to ninth aspects, comprising a Si ₃ N ₄ / SiC composite material containing 10 to ₃₀ wt% of SiC fine particles. A ceramic sintered body, having a compressive residual stress introduction layer in which a compressive residual stress is left at 250 MPa or more on a surface layer in a range of 30 to 50 μm in the depth direction from the surface of the ceramic sintered body; Further, it is made of SiO ₂ filling a crack-like groove formed so as to extend from the surface of the compressive residual stress introduction layer to the inside of the ceramic sintered body, and is positioned on both sides through the groove of the ceramic sintered body. Provided is a ceramic product characterized by having a filling joint part for joining parts to be joined.

According to the method for manufacturing a ceramic product according to the present invention, a ceramic sintered body made of a ceramic material in which SiC fine particles are dispersed or a ceramic material made of SiC is subjected to shot peening treatment to introduce compressive residual stress, and then ceramic sintering. It was generated by generating SiO ₂ by a heat treatment step in which the body was heated to a temperature lower than the heating temperature capable of removing all the compressive residual stress introduced in the shot peening process and at a temperature of 800 ° C. or higher in an oxygen-containing atmosphere. SiO ₂ repairs (heals) cracks in ceramics sintered bodies (for example, fine cracks with a depth of several μm to 10 μm), and ensures that residual compressive stress remains in the ceramic sintered body even after the heat treatment process. Can be made. For this reason, high strength can be ensured in the ceramic product, and furthermore, since the contact strength can be ensured by the presence of the compressive residual stress, the occurrence and development of cracks can be suppressed. As a result, it is possible to achieve both cancellation (or suppression) of the influence of cracks formed on the surface of the ceramic product and suppression of occurrence of cracks during use, and a ceramic product with high mechanical reliability can be obtained.
The ceramic product according to the present invention has excellent strength due to the structure having the compressive residual stress introduction layer and the filling joint portion made of SiO ₂ filling the crack-like groove, and suppresses the generation and progress of cracks. Therefore, high mechanical reliability can be secured.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
First, a method for manufacturing a ceramic product according to the present invention (hereinafter also simply referred to as a manufacturing method) and a first embodiment of the ceramic product will be described.
FIG. 1 is a diagram for explaining an example of a manufacturing method according to the present invention, in which (a) is a cross-sectional view showing a ceramic sintered body 1 (ceramic product before applying the manufacturing method according to the present invention); ) Is a view showing a state in which a surface layer portion (hereinafter also referred to as a compressive residual stress introduction layer 4) formed by introducing compressive residual stress into the ceramic sintered body 1 and a crack 2 are formed by shot peening treatment, (c). These are figures which show the ceramic product 5 obtained by performing the heat treatment process which heats the said ceramic sintered compact 1 in which the said compression residual stress introduction layer 4 and the crack 2 were formed.

  The ceramic sintered body 1 illustrated in FIG. 1 is a ceramic matrix 11 in which SiC fine particles 12 (including particles and whiskers) are dispersed (hereinafter also referred to as SiC composite ceramics). Is contained in an amount of 10 to 30 wt%.

The SiC composite ceramics that is the ceramic sintered body 1 is obtained by mixing SiC fine particles 12 in a ceramic raw material powder and sintering the mixture. By sintering, a SiC composite ceramic in which SiC fine particles 12 are dispersed in a ceramic matrix 11 formed of a ceramic raw material powder is obtained.
As the ceramic matrix 11, for example, any one selected from AlN, ZrO ₂ , Si ₃ N ₄ , Al ₂ O ₃ , and mullite (3Al ₂ O ₃ · 2SiO ₂ ) can be preferably used. However, the ceramic matrix 11 is not limited to these.

  When the content of the SiC fine particles 12 in the ceramic sintered body 1 is less than 10 wt%, a sufficient healing effect by the heat treatment process cannot be obtained, and the ceramic product 5 obtained by this manufacturing method (see FIG. 1C). Affects strength. Moreover, even if it exceeds 30 wt%, the strength of the ceramic product 5 is reduced.

  The ceramic material for forming the ceramic sintered body according to the present invention is not limited to the above-mentioned SiC composite ceramic material, for example, a SiC ceramic material (a ceramic matrix made of SiC). Can also be adopted.

  The ceramic sintered body used in the method for manufacturing a ceramic product according to the present invention is used as a structural material such as a bearing, a component for a heat engine such as a gas turbine, a spring, a gear, etc. There is no limitation. However, a thickness dimension of about several millimeters or more (shot peening treatment is performed) on a portion forming a surface (surface on which the fine particle projection material collides) to be subjected to shot peening treatment (described later) in the manufacturing method according to the present invention. Use one with a depth dimension from the surface).

In the manufacturing method illustrated in FIGS. 1A to 1C, first, the ceramic sintered body 1 is subjected to shot peening treatment to introduce compressive residual stress into the ceramic sintered body 1, and the ceramic sintered body. The crack 2 is formed in the surface 3 of 1 (refer FIG.1 (b)).
In the shot peening process, for example, a fine particle projection material 6 such as zirconia (ZrO ₂ ) beads is projected onto the ceramic sintered body 1 to introduce compressive residual stress into the ceramic sintered body 1 and to detect the surface 3 of the ceramic sintered body 1. And the formation of a crack 2 on the surface.

  Regions where compressive residual stress is introduced in the vicinity of the surface 3 of the ceramic sintered body 1 by introducing the compressive residual stress to the ceramic sintered body 1 by shot peening treatment (FIGS. 1B and 1C). A compressive residual stress introduction layer (medium code 4) is formed. The compressive residual stress introducing layer 4 is preferably formed at least about 10 μm in the depth direction from the surface 3 of the ceramic sintered body 1, and more preferably formed from the surface 3 to about 30 to 50 μm. Further, the surface 3 may be formed over a wide range of about 100 μm or more.

The crack 2 formed in the ceramic sintered body 1 by the shot peening process is a fine one having a depth from the surface 3 of about several μm to 50 μm, for example.
The crack may have a size exceeding 50 μm in depth, but the depth of the crack is preferably within 100 μm from the surface 3 of the ceramic sintered body 1.
As a result of the formation of cracks 2 in the ceramic sintered body 1 by the shot peening process, the surface 3 of the ceramic sintered body 1 is roughened.

The size (particle size), hardness, shot pressure, and other conditions of the fine particle projection material for the shot peening treatment depend on the properties of the ceramic sintered body 1 (for example, surface hardness), etc. It sets in the range which does not produce the crack of the sintered compact 1 whole. For example, a fine particle projection material 6 having a Vickers hardness (HV) of 50 to 80% of the hardness of the ceramic sintered body 1 and a particle size of 100 to 400 μm is applied to the ceramic sintered body 1 with a shot pressure of 0.1 to 0.3 MPa. It is preferable to perform shot peening processing by projecting.
Since the fine particle projection material 6 is likely to be chipped in the ceramic sintered body 1 when the particle size is increased, it is necessary to adjust so that the chipping does not occur. On the other hand, the smaller the particle size, the more difficult it is to introduce compressive residual stress. In this respect, the particle size of the fine particle projection material 6 is more preferably 100 to 200 μm. The shot pressure is more preferably 0.1 to 0.2 MPa.
Setting the particle size of the fine particle projection material 6 to 100 to 200 μm and the shot pressure to 0.1 to 0.2 MPa means that the ceramic sintered body 1 is made of, for example, Si ₃ N ₄ , Al ₂ O ₃ , and mullite as a ceramic matrix. It is particularly suitable for the shot peening process.

  The compressive residual stress introduced into the ceramic sintered body 1 by the shot peening treatment can be achieved in terms of improving the fracture toughness value of the surface 3 of the ceramic sintered body 1 after the heat treatment in the heat treatment step described later and improving the contact strength. However, the upper limit value is limited because it is necessary to prevent chipping of the ceramic sintered body 1 due to shot peening. For this reason, it is preferable that the compressive residual stress introduce | transduced into the ceramic sintered compact 1 by a shot peening process is the range of 300-1000 MPa.

Next, a heat treatment step is performed in which the ceramic sintered body 1 that has completed the above shot peening treatment is heated in an oxygen-containing atmosphere (for example, in the air).
In this heat treatment step, by heating the ceramic sintered body 1 in an oxygen-containing atmosphere, the SiC in the ceramic sintered body 1 is caused to undergo an oxidation reaction of SiC + 3 / 2O ₂ → SiO ₂ + CO to generate SiO ₂ . Let The heating temperature of the ceramic sintered body 1 in this heat treatment step is 800 ° C. or higher because of the oxidation reaction of SiC, provided that it is higher than the heating temperature at which all the compressive residual stress introduced in the shot peening process can be removed. Use a low temperature.

At this time, the generation of SiO ₂ due to the oxidation reaction of SiC involves volume expansion, so that the crack ₂ is filled with SiO _{2 as the} reaction proceeds. The crack 2 is filled with SiO ₂ produced by the oxidation reaction of SiC exposed in the crack 2.
The SiO ₂ filled in the crack 2 is solidified by cooling after the heat treatment step, thereby functioning as a bonding material (filled bonding portion 7) for bonding portions located on both sides via the crack 2 of the ceramic sintered body 1. Can be made. Therefore, as shown in FIG. 1C, the crack 2 can be cured (repaired) by filling the crack 2 with SiO ₂ by this heat treatment step.

  Moreover, as a result of the filling joint portion 7 formed in the crack 2 functioning as a joining material for joining portions located on both sides through the crack 2 of the ceramic sintered body 1, the bending strength of the ceramic sintered body 1 is increased. Can be improved. The ceramic product 5 obtained by the completion of the heat treatment step can have a higher bending strength than the ceramic sintered body 1 before performing the shot peening treatment and the heat treatment step.

As a result of enormous tests by the present inventors, compared to the ceramic sintered body 1 before forming the crack 2, the crack 2 was formed in the ceramic sintered body 1 by the shot peening treatment, and the above-described heat treatment process was performed. It was confirmed that the ceramic product 5 has higher bending strength. As a result of the bending strength test, breakage occurs in the ceramic product 5 other than the joint portion by the filling joint portion 7, so that the presence of the joint portion by the filling joint portion 7 effectively contributes to the strength improvement of the ceramic product 5. Conceivable.
In this regard, for example, by forming a large number of cracks 2 in the ceramic sintered body 1 by shot peening, and filling each crack 2 with SiO ₂ in the heat treatment process to form the filling joints 7, the ceramic product 5 It is possible to obtain higher bending strength.

As for the filling of SiO ₂ into the crack 2 in the heat treatment step, it is advantageous in terms of improving the bending strength of the ceramic product 5 to fill the entire inside of the crack 2 as in the illustrated example. _It is sufficient that the filling joint portion 7 made of SiO ₂ can function as a joining material for joining portions located on both sides via the crack 2 of the ceramic sintered body 1. There may be a portion where ₂ is not filled with SiO ₂ .
In other words, the heat treatment step can be said to be a step of improving the strength of the ceramic sintered body 1 by forming the filling joint portion 7 in the crack 2 by SiO ₂ generated by the oxidation reaction of SiC. It is considered that the filling joint portion 7 formed in the crack 2 functions to prevent the crack 2 from expanding. Moreover, it is thought that the site | part which the filling joint part 7 was formed in the crack 2 and was healed exhibits high intensity | strength, and contributes to the intensity | strength improvement of the ceramic sintered compact 1 whole.

  Setting the heating temperature of the ceramic sintered body 1 in the heat treatment step to a temperature lower than the heating temperature at which all of the compressive residual stress introduced in the shot peening process can be removed is applied to the ceramic sintered body 1 by the shot peening process. The purpose is to allow the introduced compressive residual stress to remain even after the heat treatment step is completed. By leaving the compressive residual stress after the heat treatment step is completed, the fracture toughness value of the surface 3 of the ceramic sintered body 1 can be increased. Thereby, the contact strength of the ceramic sintered body 1 can be increased, and the effect of suppressing the occurrence and development of new cracks on the surface of the ceramic product 5 can be obtained.

The compressive residual stress introduced into the ceramic sintered body 1 by the shot peening process is released by the heating of the ceramic sintered body 1 in the heat treatment step and decreases (for example, see FIG. 3). The compressive residual stress greatly decreases as the heating temperature in the heat treatment step increases.
In terms of increasing the contact strength of the ceramic product 5 and suppressing the occurrence and development of cracks on the surface, it is preferable that a compressive residual stress as large as possible is ensured (remains) after the heat treatment step is completed.

FIG. 3 shows a case where 20 wt% SiC particles having an average particle diameter of 0.27 μm are mixed (mixed) with Si ₃ N ₄ powder and 8 wt% Y ₂ O ₃ is used as a sintering aid in nitrogen gas. The ceramic sintered body obtained by performing pressure sintering at 1850 ° C. for 2 hours with a compressive stress of 35 MPa applied is subjected to shot peening treatment, followed by heat treatment (heat treatment step). After producing a plurality of test pieces having different (heating temperatures), data obtained by measuring the compressive residual stress on the surface of the ceramic sintered body (surface subjected to shot peening treatment) by X-ray diffraction for each test piece (FIG. 3) (SP). The heat treatment was performed by heating in the atmosphere for 1 hour.
The shot peening treatment is performed by projecting ZrO ₂ beads (Vickers hardness (HV) 1250) having an average particle diameter of 300 μm at a shot pressure of 0.2 MPa, a coverage of 300%, and a shot time of 30 to 40 seconds, and remaining compressed on the ceramic sintered body. A stress introducing layer and a crack (surface defect) were formed. FIG. 3 also shows the compressive residual stress (not SP in FIG. 3) of the ceramic sintered body before the shot peening treatment.

In addition, as shown in FIG. 4, for the above-described test piece, the tendency to decrease the compressive residual stress with respect to the heating time (heat treatment time h) in the heat treatment step was confirmed. In any case of 1000 ° C., it was confirmed that the compressive residual stress could be maintained even after the heat treatment for 10 hours from the start of the heat treatment.
In FIG. 4, the compressive residual stress (SP material in FIG. 4) of the ceramic sintered body that has not been heat-treated after the above-described shot peening treatment is also shown.

  In the heat treatment process, if the heating temperature of the ceramic sintered body 1 is kept lower than the heating temperature at which all the compressive residual stress introduced by the shot peening process can be removed, a large amount of the compressive residual stress introduced by the shot peening process remains. Can be made. On the other hand, if the heating temperature of the ceramic sintered body 1 in the heat treatment step is lower than 800 ° C., the oxidation reaction of the SiC particles 12 does not proceed sufficiently, the formation of the filling joint 7 becomes insufficient, and the bending strength is improved. It becomes difficult. For this reason, the heating temperature of the ceramic sintered body 1 in the heat treatment step is set to 800 ° C. or higher and lower than the heating temperature at which all the compressive residual stress introduced in the shot peening process can be removed.

For example, in the case of the ceramic sintered body 1 using silicon nitride (Si ₃ N ₄ ) as a ceramic matrix, the heating temperature of the ceramic sintered body 1 in the heat treatment step is preferably 800 ° C. or higher and lower than 1200 ° C. . In the case of this ceramic sintered body 1, the compressive residual stress introduced into the ceramic sintered body 1 by the shot peening process is almost completely removed when the heating temperature of the ceramic sintered body 1 in the heat treatment process is around 1300 ° C. (1300 ° C. is a heating temperature at which all the compressive residual stress introduced by the shot peening process can be removed), which approximates the state before the introduction by the shot peening process (see, for example, FIG. 3).
Further, as can be seen with reference to FIG. 3, it was found that when the heating temperature (heat treatment temperature) in the heat treatment step is 1250 ° C., the attenuation width of the residual stress is slightly larger. For this reason, it is preferable that the upper limit of the heat treatment temperature is 1100 ° C. or 1000 ° C.

In the case of the ceramic sintered body 1 that is a Si ₃ N ₄ / SiC composite, if the heating temperature of the ceramic sintered body 1 in the heat treatment step is 1100 ° C., the compression residual introduced into the ceramic sintered body 1 by shot peening treatment About one third of the stress (compressive residual stress of the surface 3 of the ceramic sintered body 1) can be reliably maintained. Therefore, for example, by introducing a compressive residual stress of 800 to 1000 MPa (compressive residual stress of the surface 3 of the ceramic sintered body 1) by shot peening treatment, a compressive residual of 250 MPa or more is applied to the ceramic sintered body 1 after the heat treatment. Stress (compressive residual stress of the surface 3 of the ceramic sintered body 1) can be reliably ensured, and an effect of suppressing the generation and development of new cracks can be reliably obtained.

Since also occurs generation of SiO ₂ by oxidation reactions of the SiC fine particles exposed on the surface 3 of the sintered ceramics 1 is performed a heat treatment process, and fine very fine scratches on the surface 3 of the sintered ceramics 1 Void surface defects are also healed.

In the manufacturing method described above, after forming the compressive residual stress introducing layer 4 and the crack 2 in the ceramic sintered body 1 by shot peening, the filling joint 7 is formed in the crack 2 of the ceramic sintered body 1 by a heat treatment process. However, the present invention is not limited to this.
In the manufacturing method according to the present invention, the formation of cracks on the surface of the ceramic sintered body may be performed at any time before the heat treatment step, and is not limited to a configuration in which the formation of cracks is performed by shot peening. It is also possible to adopt a configuration in which the crack is formed before or after the shot peening process. It is also possible to use a ceramic sintered body having a crack formed on the surface during transportation after sintering or use as a structural material. In any case, the contact strength and bending strength of the ceramic sintered body can be improved by performing a heat treatment step after the shot peening treatment.
In this respect, the following manufacturing methods (A) and (B) can also be employed. However, the heat treatment step is performed at a temperature lower than the heating temperature at which all the compressive residual stress introduced in the shot peening process can be removed, and the compressive residual stress remains in the ceramic sintered body after the heat treatment.

(A) Second Embodiment As shown in FIGS. 2A to 2C, a ceramic sintered body 21 in which a crack 22 is formed on the surface by use as a structural material, machining, or the like (FIG. 2A). (See FIG. 2B), the same shot peening process as in the first embodiment described above is performed to form the compressive residual stress introduction layer 4 on the ceramic sintered body 21 (see FIG. 2B), and then the first embodiment described above. A ceramic product 23 is obtained by performing a heat treatment step similar to that of the embodiment.
The material of the ceramic sintered body 21 used in the manufacturing method of this embodiment is the same as that of the ceramic sintered body 1 described in the first embodiment.
Also in this case, in the shot peening process, the compressive residual stress introduction layer 4 is formed on the ceramic sintered body 21 and the crack 2 is formed on the surface of the ceramic sintered body 21 as in the first embodiment. Therefore, the bending strength of the ceramic sintered body 21 can be improved by performing the heat treatment step.

(B) Third Embodiment A shot peening treatment is applied to a ceramic sintered body formed of the same material as the ceramic sintered body 1 described in the first embodiment, and compression residual stress is introduced into the ceramic sintered body. After forming the layer, cracks are formed on the surface of the ceramic sintered body by, for example, a Vickers indenter indentation test or machining, and then the same heat treatment step as described above is performed to obtain a ceramic product. In this case, it is possible to perform a heat treatment step after performing a strength test such as a Vickers hardness test.
In the case of this embodiment, for example, a ceramic sintered body to be subjected to shot peening treatment is used that has no cracks on the surface, and after performing shot peening treatment to form a compressive residual stress introduction layer and cracks, Furthermore, it is possible to form a crack in the surface of the ceramic sintered body and then perform a heat treatment step similar to that in the first embodiment described above. In addition, it does not exclude the use of a ceramic sintered body to be subjected to shot peening treatment having a crack on the surface.

  In addition, in terms of improving the strength of the ceramic sintered body, it is more effective to perform shot peening treatment under conditions that can form cracks on the surface of the ceramic sintered body. In the second and third embodiments described above, The use of a shot peening process under conditions that do not form cracks is not excluded by using a fine particle projection material having a low hardness or by keeping the shot pressure low.

(Machining)
In the manufacturing method according to the present invention, the ceramic sintered body can be subjected to machining such as drilling, cutting and grinding before the heat treatment step.
For example, in the second embodiment described above, the use of the ceramic sintered body 21 in which the cracks 22 are formed on the surface by machining has been described. Separately, the ceramic sintered body is machined after the shot peening treatment. You can go. Further, the machining may be performed during the shot peening process.
The machining of the ceramic sintered body may be performed any time before the heat treatment step, and this is common to the first to third embodiments described above. Further, the machining described here does not require the formation of cracks on the surface of the ceramic sintered body. What does not form a crack may be sufficient.

Even when the ceramic sintered body is machined before the heat treatment step, the contact strength and bending strength of the ceramic sintered body can be improved by performing the heat treatment step after completing the machining and shot peening treatment. it can.
Moreover, since the crack formed in the ceramic sintered body by the machining is healed, this healing portion also contributes to the improvement of the bending strength of the ceramic sintered body.

(Heat treatment process under bending stress)
The heat treatment step may be performed in a state where a bending stress is applied as a load stress to the ceramic sintered body.
For example, without removing the ceramic sintered body attached to the apparatus, the ceramic sintered body is subjected to the shot peening treatment and the heat treatment process in the attached state (while the bending stress is applied). It is also possible to do it.

(Verification 1: Verification of strength characteristics)
The test materials (ceramic sintered bodies) of the following Examples 1-9 and Comparative Examples 1-18 were prepared and subjected to a bending test to verify strength characteristics.

(Examples 1, 2, and 3: “SP + VC + heat treated material” in FIGS. 6 and 9)
20 wt% SiC particles with an average particle size of 0.27 μm are mixed (mixed) in Si ₃ N ₄ powder and 8 wt% Y ₂ O ₃ is used as a sintering aid, compressed in nitrogen gas at 35 MPa While being applied with stress, it was heated at 1850 ° C. for 2 hours to perform pressure sintering. A test piece (ceramic sintered body) cut into a size of 3 mm × 4 mm × 22 mm from the sintered body was produced.
Next, ZrO ₂ beads (Vickers hardness (HV) 1250) having an average particle size of 300 μm were projected onto a 4 mm × 22 mm size surface (hereinafter also referred to as a surface) of the test piece, and a shot peening treatment was performed. This shot peening process was performed using a direct pressure shot peening apparatus with a shot pressure of 0.2 MPa, a coverage of 300%, and a shot time of 30 to 40 seconds. As shown in FIG. 5, it was confirmed by X-ray diffraction that compressive residual stress could be introduced from the surface of the test piece to about 40 μm. Further, it was confirmed that the introduced compressive residual stress was the largest on the surface of the test piece and showed a distribution that decreased as the distance from the surface (distance in the depth direction from the surface) increased. The measured value of the compressive residual stress on the surface of the test piece was 876 MPa. In FIG. 5, the value of the compressive residual stress on the vertical axis is displayed as a negative value, but it goes without saying that the magnitude of the compressive residual stress that can be introduced can be grasped as an absolute value.
Moreover, when the test piece after a shot peening process was investigated, it confirmed that many fine cracks with a depth of several micrometers were formed in the surface.

Next, a pre-crack (hereinafter sometimes abbreviated as Vickers crack) is introduced by applying an indentation load of the indenter to the surface of the test piece after the shot peening treatment using a Vickers hardness tester. Was heat-treated at 1100 ° C. for 1 hour in the air.
However, in order to grasp the relationship between the indentation load of the Vickers indenter (hereinafter also referred to as “Vickers indentation load”) and the bending strength, the introduction of the Vickers crack is performed with the Vickers indentation load of 19.6 N (Example 1), 29.4 N. (Example 2), 49N (Example 3), and 98N (Example 4) were set in four ways to obtain four types of test materials. Then, a three-point bending test was performed on these specimens (SP + VC + heat treated material), and the results are shown in FIG. Further, the length of the Vickers crack 30a on the surface of the test piece 30 (surface crack length; reference numeral 2C shown in FIG. 12) is measured, and the relationship between the surface crack length of the Vickers crack and the bending strength is collectively shown in FIG. It was.
In FIG. 12, reference numeral 30b denotes an indentation formed by pushing a Vickers indenter.

(Examples 5, 6, 7, and 8: “VC + SP + heat treated material” in FIGS. 7 and 10)
After introducing a Vickers crack on the surface of the test piece, a shot peening treatment was performed under the same conditions as in the production of the SP + VC + heat treated material, and then the same heat treatment as in the production of the SP + VC + heat treated material was performed. It is the same as SP + VC + heat treated material except that the introduction of Vickers cracks to the test piece is performed before the shot peening treatment. In the introduction of the Vickers crack, the Vickers indentation load is set to 4 types of 19.6N (Example 5), 29.4N (Example 6), 49N (Example 7), and 98N (Example 8), and four types are set. A specimen was obtained. Then, a three-point bending test was performed on these specimens (VC + SP + heat treated material). FIG. 7 shows the relationship between the Vickers indentation load and the bending strength, and FIG. 10 shows the relationship between the surface crack length of the Vickers crack and the bending strength.

(Example 9: “SP + heat treatment material” in FIGS. 6 and 9)
A sample material (Example 9) was obtained in the same manner as the preparation of SP + VC + heat treated material except that the introduction of Vickers crack was omitted. The results of a three-point bending test performed on this specimen (SP + heat treated material) are shown in the column “No pre-cracking” in FIGS. 6 and 9.

(Comparative Examples 1, 2, 3, 4: “SP + VC material” in FIGS. 6 and 9)
Except that the heat treatment was omitted, a test material was produced in the same manner as the production of SP + VC + heat treated material (Examples 1, 2, 3, 4). This test material is obtained by introducing a Vickers crack after performing the same shot peening treatment as that of SP + VC + heat treated material on a 3 mm × 4 mm × 22 mm size three-point bending test piece obtained by sintering the raw material. The introduction of the Vickers crack is performed by setting the Vickers indentation load to 4 types of 19.6N (Comparative Example 1), 29.4N (Comparative Example 2), 49N (Comparative Example 3), and 98N (Comparative Example 4). Four kinds of test materials were obtained. A three-point bending test was performed on these specimens (SP + VC material). FIG. 6 shows the relationship between the Vickers indentation load and the bending strength, and FIG. 9 shows the relationship between the surface crack length of the Vickers crack and the bending strength.

(Comparative examples 5, 6, 7, 8: “VC + SP material” in FIGS. 7 and 10)
Except that the heat treatment was omitted, a test material was produced in the same manner as the production of the above-described VC + SP + heat treated material (Examples 5, 6, 7, 8). This test material was obtained by introducing a Vickers crack into a 3 mm × 4 mm × 22 mm size three-point bending test piece obtained by sintering a raw material and then performing the same shot peening treatment as SP + VC + heat treated material. The introduction of the Vickers crack is performed by setting the Vickers indentation load to 4 types of 19.6N (Comparative Example 5), 29.4N (Comparative Example 6), 49N (Comparative Example 7), and 98N (Comparative Example 8). Four kinds of test materials were obtained. A three-point bending test was performed on these specimens (VC + SP material). FIG. 7 shows the relationship between the Vickers indentation load and the bending strength, and FIG. 10 shows the relationship between the surface crack length of the Vickers crack and the bending strength.

(Comparative Example 9: “SP material” in FIGS. 6 and 9)
Except that the heat treatment was omitted, a test material was produced in the same manner as in the production of the SP + heat treatment material (Example 9) described above (Comparative Example 9). This test material (SP material) is obtained by subjecting a 3 mm × 4 mm × 22 mm size three-point bending test piece obtained by sintering raw materials to the same shot peening treatment as SP + VC + heat treated material. Vickers cracks are not introduced.
The results of the three-point bending test performed on this specimen are shown in the “No crack” column of FIGS. 6 and 9.

(Comparative Example 10: “Non-SP material” in FIGS. 8 and 11)
Comparative Example 10 was a test material that was not subjected to shot peening treatment, introduction of Vickers cracks, or heat treatment on a 3 mm × 4 mm × 22 mm size three-point bending test piece obtained by sintering the raw material.
The results of a three-point bending test performed on this specimen (non-SP material) are shown in the column “No pre-cracking” in FIGS.

(Comparative Examples 11, 12, 13, and 14: “Non-SP + VC material” in FIGS. 8 and 11)
Except that the shot peening treatment and the heat treatment were omitted, a test material was produced in the same manner as the production of the SP + VC + heat treatment material. This test material is obtained by introducing a Vickers crack into a three-point bending test piece having a size of 3 mm × 4 mm × 22 mm obtained by sintering a raw material. Shot peening and heat treatment are not performed. The introduction of the Vickers crack is performed by setting the Vickers indentation load to 4 types of 19.6N (Comparative Example 11), 29.4N (Comparative Example 12), 49N (Comparative Example 13), and 98N (Comparative Example 14), Four kinds of test materials were obtained. A three-point bending test was performed on these test materials (non-SP + VC materials). FIG. 8 shows the relationship between the Vickers indentation load and the bending strength, and FIG. 11 shows the relationship between the surface crack length of the Vickers crack and the bending strength.

(Comparative Examples 15, 16, 17, and 18: “Non-SP + VC + Heat Treatment Material” in FIGS. 8 and 11)
Except that the shot peening treatment was omitted, a test material was prepared in the same manner as the SP + VC + heat treated material. This test material is obtained by introducing a Vickers crack into a 3 mm × 4 mm × 22 mm size three-point bending test piece obtained by sintering the raw material and then performing a heat treatment. The introduction of the Vickers crack is performed by setting the Vickers indentation load to 4 types of 19.6N (Comparative Example 15), 29.4N (Comparative Example 16), 49N (Comparative Example 17), and 98N (Comparative Example 18). Four kinds of test materials were obtained. A three-point bending test was performed on these specimens (non-SP + VC + heat treated material). FIG. 8 shows the relationship between the Vickers indentation load and the bending strength, and FIG. 11 shows the relationship between the surface crack length of the Vickers crack and the bending strength.

As described above, when the SP + VC + heat treated material was produced, fine cracks having a depth of several μm were formed on the surface immediately after the shot peening treatment.
This is the same for other specimens subjected to shot peening treatment. For the VC + SP + heat treated material, SP + heat treated material, SP + VC material, VC + SP material, SP material, a test piece immediately after the shot peening treatment is prepared. It was confirmed that fine cracks having a depth of several μm were formed on the surface.

The specimen prepared by introducing the Vickers crack is the depth of the Vickers crack with respect to the Vickers indentation load when the Vickers crack is introduced after the shot peening process (SP + VC + heat treated material, SP + VC material is applicable). It was shallower than the other specimens prepared by introducing Vickers cracks, and the length (reference numeral 2C shown in FIG. 12) was also short.
As shown in FIG. 13, the Vickers crack 30 a introduced into the test piece 30 (ceramic sintered body) is formed in a substantially semicircular shape centering on the indentation 30 b in the depth direction from the surface of the test piece 30. For this reason, the depth of the Vickers crack is deepest in the vicinity of the indentation 30b, and the dimension (depth dimension) can be regarded as almost half of the surface crack length 2C. As apparent from FIG. 9, FIG. 10, and FIG. 11, the surface crack length 2C of the Vickers crack of the SP + VC + heat treated material (FIG. 9) and the SP + VC material (FIG. 9) is VC + SP material (FIG. 10), VC + SP +. It was possible to grasp the tendency that the surface crack length 2C of the Vickers crack of the heat treated material (FIG. 10), the non-SP + VC material (FIG. 11), and the non-SP + VC + heat treated material (FIG. 11) was shorter.
14A shows a Vickers crack 31 formed in the non-SP + VC material, and FIG. 14B shows a Vickers crack 32 formed in the SP + VC material with the same Vickers indentation load as in FIG. 14A.
As shown in FIGS. 14A and 14B, the length of the Vickers crack 32 of the SP + VC material is considerably shorter than the length of the Vickers crack 31 formed in the non-SP + VC material.

This is because the fracture toughness of the specimen surface is enhanced by the action of the compressive residual stress introduced by the shot peening process, and the occurrence and propagation of cracks is suppressed by improving the fracture toughness, and the length of the Vickers crack is reduced. It will be shorter.
As shown in Table 1, when the fracture toughness value of the surface was measured by the IF method (Indentation Fracture method: JIS R1607) for the non-SP material and the SP material, the fracture toughness value of the SP material was 130- It was improved by 150%. In addition, the measurement was performed about three kinds of Vickers indentation loads 29.4N, 49N, and 98N.

(Consideration of test results)
As can be seen with reference to FIGS. 6 to 11, the SP + VC + heat treated material and the VC + SP + heat treated material according to the present invention were able to improve the bending strength compared to the non-SP + VC material that was not subjected to shot peening and heat treatment. The SP + heat-treated material according to the present invention was able to improve the bending strength compared to the non-SP material that was not subjected to shot peening and heat treatment.
Further, the SP + VC material, the VC + SP material subjected only to the shot peening treatment among the shot peening treatment and the heat treatment, and the non-SP + VC + heat treated material subjected only to the heat treatment were able to improve the bending strength as compared with the non-SP + VC material.

As shown in FIGS. 7 and 10, the VC + SP + heat treatment material in which the shot peening treatment and the heat treatment are performed after the introduction of the Vickers crack is bent higher than the VC + SP material in which the shot peening treatment is performed after the introduction of the Vickers crack and the heat treatment is not performed. Strength was obtained.
The technique of improving the fracture toughness value on the surface of ceramic products by shot peening treatment as in Patent Document 1 (the peening method described above, crack healing by heat treatment as in the present invention is not performed) has already cracks on the surface. When applied to ceramic products, if the depth of cracks is small and shallower than the depth of introduction of compressive residual stress introduced into the ceramic sintered body by shot peening, the surface fracture toughness value is improved by compressive residual stress. Is considered to contribute to the improvement of bending strength. For this reason, when the depth of the crack exceeds the depth of introduction of compressive residual stress by shot peening treatment, the improvement of the surface fracture toughness value due to the compressive residual stress does not sufficiently contribute to the improvement of bending strength, and the strength improvement effect is achieved. It is thought that it will become smaller.
In contrast, the VC + SP + heat treated material according to the present invention, as can be seen with reference to FIG. 10, has a bending strength greater than that of the VC + SP material when the Vickers crack depth is 50 μm or more (surface crack length 2C is 100 μm). It is clear that can be improved. This is considered to be because, in the VC + SP + heat treated material, since the Vickers crack was healed by the heat treatment, the influence of the Vickers crack on the bending strength of the test material was suppressed.

As described above, the VC + SP + heat treated material and the VC + SP material have a depth of introduction of compressive residual stress by shot peening treatment of about 40 μm. Therefore, the VC + SP + heat treated material has a depth of introduction of compressive residual stress compared to the VC + SP material. This effectively contributes to the improvement of the bending strength of the ceramic sintered body in which cracks with a depth exceeding 1 are formed.
In addition, for VC + SP + heat treated material, although residual compressive stress introduced by shot peening treatment is attenuated by heat treatment after shot peening treatment, it can be confirmed that the bending strength exceeding VC + SP material can be ensured by cracking by heat treatment. It was.

As shown in FIG. 6, the SP + VC + heat treated material was able to greatly improve the bending strength compared to the SP + VC material that was not heat treated. Even when a crack was formed in the shot peened sample, it was confirmed that the bending strength could be improved by curing the crack by heat treatment.
Further, for this SP + VC + heat treated material, fracture outside the crack occurred when the Vickers indentation load was 49 N or less (see FIG. 6), the surface crack length 2C was 130 μm or less (see FIG. 9). That is, it was confirmed that the Vickers crack was made harmless. For this SP + VC + heat treated material, when the Vickers indentation load is 49 N or less (see FIG. 6), the surface crack length 2C is 130 μm or less (see FIG. 9), the influence of the Vickers crack on the bending strength can be canceled. I can say that.

  Also, the SP + heat treated material according to the present invention was able to improve the bending strength compared to the SP material not subjected to heat treatment. The SP + heat-treated material is considered to contribute to the improvement of bending strength by the fact that minute cracks formed on the surface of the test material (surface layer) by the shot peening treatment are cured by the heat treatment.

(Verification of the effect of heat treatment temperature on fracture toughness value 1)
A sample material produced by changing the heat treatment for producing the SP + heat treatment material to 1000 ° C. for 1 hour and a sample material produced by changing the heat treatment to 1300 ° C. for 1 hour were produced, and the IF method was used. The fracture toughness value of the surface was measured. The measurement was performed for three kinds of Vickers indentation loads of 29.4N, 49N, and 98N.
As a result, as shown in Table 1, it was confirmed that the specimens subjected to heat treatment at 1000 ° C. for 1 hour were able to secure a higher fracture toughness value than the unSP material. On the other hand, the fracture toughness value of the test material subjected to heat treatment at 1300 ° C. for 1 hour was greatly reduced as compared with the test material subjected to heat treatment at 1000 ° C. for 1 hour.

(Verification of the effect of heat treatment temperature on fracture toughness value 2)
Further, as shown in FIG. 15, the test piece (SP material described above) subjected to the shot peening treatment was prepared by setting the heat treatment temperature in increments of 100 ° C. from 800 to 1300 ° C. and performing the heat treatment for 1 hour each. Specimens were prepared, and fracture toughness values were measured for each specimen by IF method. However, the Vickers indentation load was 49N. In addition, the above-mentioned non-SP material and SP material were also measured.
As shown in FIG. 15, the fracture toughness value tended to decrease as the heat treatment temperature for producing the specimen was increased. Further, at the heat treatment temperature of 1300 ° C., the fracture toughness value was greatly reduced as compared with the heat treatment temperature of 1200 ° C.

  The SP + VC + heat treated material, VC + SP + heat treated material, and SP + heat treated material according to the present invention can cancel (detoxify) or suppress the influence of the Vickers crack on the bending strength due to the heat treatment (heat treatment step), and also after the heat treatment. The compressive residual stress remaining in the specimen contributes to the improvement of the fracture toughness value of the specimen (ceramic sintered body) surface. As described above, the compressive residual stress remaining in the specimen after heat treatment increases the fracture toughness value of the specimen (ceramic sintered body) surface and suppresses the development of new Vickers cracks and new cracks. Fulfills the function of As a result, high mechanical reliability can be obtained.

(Evaluation 2: Evaluation of contact strength)
As shown in FIG. 16, three types of specimens prepared by heat treatment at a heat treatment temperature of 900 ° C., 1100 ° C., and 1300 ° C. were prepared on the shot peened test piece (the SP material described above). The indentation test of a WC (tungsten carbide) sphere having a diameter of 4.0 mm was performed on the three kinds of test materials and the above-described non-SP material and SP material.
The indentation load P (ball indenter indentation load in FIG. 16) was set in increments of 0.5 kN from 0.5 to 4.5 kN, and indentation was performed at an indentation load speed of 2.0 kN / min, and the desired test load was reached. By unloading, the surface of the test material was observed with an optical microscope, and it was confirmed whether ring cracks (see reference numeral 41 in FIGS. 19A and 19B) were generated.
In FIGS. 19A and 19B, reference numeral 42 denotes a test material, and 43 denotes a ball indenter (WC sphere). 19A is a view showing a state in which the ball indenter 43 is pushed into the test material 42, and FIG. 19B is a plan view showing the ring crack 41 formed in the test material 42 by the push of the ball indenter 43. It is.

A ball indenter is pushed into the three points of the specimen with the same indentation load P, and the limit load (indentation load P) at which no ring crack occurs at all three points is defined as the crack initiation limit load Pc. The crack initiation limit load Pc was determined for. The crack initiation limit load Pc is indicated by a symbol Pc in FIG.
As a result of the indentation test, the crack initiation limit load Pc of the non-SP material was 0.5 kN. The SP material did not generate ring cracks even at the maximum load of 4.5 kN that can be tested, and it was confirmed that the crack initiation limit load Pc was significantly improved as compared with the non-SP material. Further, three kinds of test materials obtained by heat-treating the SP material (in FIG. 16, SP + 900 ° C. × 1 h heat treatment (Example 10), SP + 1100 ° C. × 1 h heat treatment (Example 11), SP + 1300 ° C. × 1 h heat treatment ( In Comparative Example 19)), it was confirmed that the crack initiation limit load Pc was significantly improved as compared with the non-SP material. Moreover, about three types of test materials obtained by heat-treating SP material, the crack initiation limit load Pc decreased as the heat treatment temperature increased.

Next, for each test material, the crack initiation limit stress σc is calculated from Hertz's elastic contact theoretical formula (Formula 1 below, Japan Tribology Society, Ceramics Tribology, 51-57, Yokendo (2003)). The results are shown in FIG.
In Equation 1, W is the indentation load, ν ₁ is the Poisson's ratio of the specimen, and a is the contact circle radius. The contact circle radius a is given by Equation 2 below. In Equation 2, R is the radius of the ball indenter, W is the indentation load, ν ₁ is the Poisson's ratio of the specimen, ν ₂ is the Poisson's ratio of the spherical indenter, E ₁ is the Young's modulus of the specimen, and E ₂ is the spherical indenter. Young's modulus.

In addition, the apparent fracture toughness value K _IC was calculated for each specimen, and the results are summarized in FIG. The fracture toughness value K _IC was calculated according to the calculation method of the fracture toughness value K _IC in the IF method.

The σc of the SP material was 3.4 GPa or more, which showed a significant improvement of 100% or more compared with 1.6 GPa of the non-SP material.
In addition, three kinds of test materials obtained by heat-treating the SP material also improved the crack initiation limit stress σc compared to the non-SP material, but the improvement rate was lower than that of the SP material.
The apparent fracture toughness value K _{IC on the} surface of the SP material was 9.6 MPa · m ^1/2 , which was an improvement of 134% compared to 4.2 MPa · m ^1/2 of the non-SP material. In the three types of specimens obtained by heat-treating the SP material, the improvement rate decreased with increasing temperature. The measurement results of the crack initiation limit stress σc and the apparent fracture toughness value K _IC are consistent with the tendency of the measurement results of the compressive residual stress. Therefore, it is considered that the significant improvement in the crack initiation limit stress σc and the apparent fracture toughness value K _IC are attributed to the compressive residual stress introduced into the surface.

(Evaluation 3: Evaluation of critical stress for crack healing)
A pre-crack (surface length 2c = 100 μm) is introduced into the SP material described above with a Vickers indentation load of 49 N, and heat treatment (heat treatment process) under stress is performed under a constant stress of 300 to 450 MPa of load stress (bending stress). It was. The heat treatment conditions were 1100 ° C. and 5 hours in the air (hereinafter also referred to as “SP + stressed heat treatment material. Example 12”).
As a comparative material, (1) 100 μm pre-cracked material in which a pre-crack having a surface length of 100 mm was introduced with 19.6 N of a Vickers indentation load was subjected to the same heat treatment as SP + VC + stressed heat-treated material. Heat treatment material similar to SP + VC + stressed heat treatment material (hereinafter referred to as SP + VC + stressed heat treated material) was applied to a non-SP + stressed heat treated material 1. Comparative Example 20 What was done (hereinafter, non-SP + heat-treated material 2 under stress, Comparative Example 21) was prepared.

  FIG. 18 shows the load stress during the heat treatment and the room temperature bending strength after the heat treatment. The critical stress capable of crack healing at 1100 ° C. of the heat-treated material under SP + stress was 400 MPa. This critical stress greatly exceeded 300 MPa of the unSP + stressed heat treated material 1 having the same crack of about 100 μm and 200 MPa of the unSP + stressed heat treated material 2 having the crack introduced at the same load. That is, the SP + stressed heat-treated material was able to greatly improve the limit stress capable of crack healing both when having cracks of the same size or when cracks were generated by the same level of impact.

In addition, this invention is not limited to the above-mentioned embodiment, It can change suitably.
The present invention can also be applied to a product (ceramic sintered body) in use as a structural material, for example. The ceramic product according to the present invention can be obtained by performing shot peening treatment and heat treatment (heat treatment step) on the product in use.
The ceramic product according to the present invention includes those in which a protective layer is separately provided on the surface of the ceramic sintered body by coating or the like.

(A)-(c) is a figure which shows 1st Embodiment of the manufacturing method of the ceramic product based on this invention. (A)-(c) is a figure which shows 2nd Embodiment of the manufacturing method of the ceramic product based on this invention. It is a figure which shows the depth direction distribution of the compressive residual stress introduced into the ceramic sintered compact by the shot peening process. It is a figure which shows the influence which the heat processing time of the ceramic sintered compact after a shot peening process has on a compressive residual stress. It is a figure which shows the reduction | decrease of the compressive residual stress by the heat processing of the ceramic sintered compact after a shot peening process. It is a figure which shows the influence which a shot peening process and heat processing have on the bending strength of a ceramic sintered compact, and the relationship between the Vickers indentation load and bending strength for introduction of a Vickers crack about SP + VC material and SP + VC + heat treatment material, and SP material The bending strength of SP + heat-treated material is summarized. It is a figure which shows the influence which the shot peening process and heat processing have on the bending strength of a ceramic sintered compact, and the relationship between the Vickers pushing load and bending strength for introduction of a Vickers crack about VC + SP material and VC + SP + heat treatment material, and SP material The bending strength of SP + heat-treated material is summarized. It is a diagram showing the effect of shot peening treatment, heat treatment on the bending strength of ceramic sintered body, the relationship between Vickers indentation load and bending strength for the introduction of Vickers cracks for non-SP + VC material, non-SP + VC + heat treated material, and The bending strength of non-SP material and non-SP + VC + heat treated material is shown collectively. It is a figure which shows the influence which the shot peening process and heat processing have on the bending strength of a ceramic sintered compact, The relationship between the surface crack length of the Vickers crack introduced into SP + VC material and SP + VC + heat processing material, and bending strength, SP material, SP + The bending strength of heat-treated materials is summarized. It is a figure which shows the influence which the shot peening process and heat processing have on the bending strength of a ceramic sintered compact, The relationship between the surface crack length and bending strength of the Vickers crack introduced into VC + SP material, VC + SP + heat processing material, and SP material, SP + The bending strength of heat-treated materials is summarized. It is a figure which shows the influence which the shot peening process and the heat processing have on the bending strength of the ceramic sintered body, and the relationship between the surface crack length of the Vickers crack introduced into the non-SP + VC material, the non-SP + VC + heat treated material and the bending strength, and the non-SP The bending strength of the material, non-SP + VC + heat treated material is summarized. It is a figure which shows an example of the Vickers crack formed in the ceramic sintered compact. It is a figure which shows the formation range in the depth direction from the ceramic sintered compact surface of the Vickers crack formed in the ceramic sintered compact. (A) is a figure which shows the Vickers crack formed in the ceramic sintered compact which has not performed shot peening processing, (b) is a figure which shows the Vickers crack formed in the ceramic sintered compact after shot peening processing. It is a figure which shows the relationship between the heat processing temperature of a ceramic sintered compact, and a fracture toughness value. It is a figure which shows the relationship between the heat processing temperature of a ceramic sintered compact, and a ball indenter indentation load. It is a figure which shows the relationship between the heat processing temperature of a ceramic sintered compact, a crack generation critical stress, and a fracture toughness value. It is a figure which shows the influence which the applied stress applied at the time of the heat processing of a ceramic sintered compact has on the limit stress which can be crack-healed. (A), (b) is a figure explaining the generation | occurrence | production state of the ring crack in a ball | bowl indenter indentation test.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Ceramic sintered compact, 11 ... Ceramic matrix, 12 ... SiC fine particle, 2 ... Crack, 3 ... Surface, 4 ... Compressive residual stress introduction layer, 5 ... Ceramic product, 6 ... Fine particle projection material, 7 ... Filling junction part, DESCRIPTION OF SYMBOLS 21 ... Ceramic sintered compact, 22 ... Crack, 23 ... Ceramic product, 30a ... Vickers crack, 30b ... Indentation, 31, 32 ... Vickers crack, 41 ... Ring crack, 42 ... Test material, 43 ... Ball indenter (WC sphere ).

Claims (10)

By introducing compressive residual stress into the ceramic sintered body made of a Si ₃ N ₄ / SiC composite material containing 10 to ₃₀ wt% of SiC fine particles by shot peening treatment, the ceramic sintered body has a depth of 30 from the surface of the ceramic sintered body. After forming a compressive residual stress introduction layer introduced in the range of 800 to 1000 MPa of compressive residual stress in the surface layer portion in a range of up to 50 μm, and forming a crack in the ceramic sintered body,
The ceramic sintered body is heated in an oxygen-containing atmosphere to a temperature of 1100 ° C. or lower and 800 ° C. or higher, which is lower than the heating temperature at which all the compressive residual stress introduced by the shot peening treatment can be removed. A ceramic product characterized by performing a heat treatment step of oxidizing SiC in the body to produce SiO ₂ and leaving a compressive residual stress of 250 MPa or more in a compressive residual stress introduction layer in a surface layer portion of the ceramic sintered body Production method. Si ₃ N ₄ / SiC composite material containing 10 to ₃₀ wt% of SiC fine particles, and by introducing compressive residual stress to the ceramic sintered body having cracks on the surface by shot peening treatment, the surface of the ceramic sintered body After forming a compressive residual stress introduction layer in which a compressive residual stress is introduced in the range of 800 to 1000 MPa on the surface layer portion in the range of 30 to 50 μm in the depth direction,
The ceramic sintered body is heated in an oxygen-containing atmosphere to a temperature of 1100 ° C. or lower and 800 ° C. or higher, which is lower than the heating temperature at which all the compressive residual stress introduced by the shot peening treatment can be removed. A ceramic product characterized by performing a heat treatment step of oxidizing SiC in the body to produce SiO ₂ and leaving a compressive residual stress of 250 MPa or more in a compressive residual stress introduction layer in a surface layer portion of the ceramic sintered body Production method. By introducing compressive residual stress into the ceramic sintered body made of a Si ₃ N ₄ / SiC composite material containing 10 to ₃₀ wt% of SiC fine particles by shot peening treatment, the ceramic sintered body has a depth of 30 from the surface of the ceramic sintered body. A compressive residual stress-introduced layer is formed on the surface layer in the range of up to 50 μm and a compressive residual stress is introduced in the range of 800 to 1000 MPa, and cracks are formed on the surface of the ceramic sintered body after the shot peening treatment is completed. After
The ceramic sintered body is heated in an oxygen-containing atmosphere to a temperature of 1100 ° C. or lower and 800 ° C. or higher, which is lower than the heating temperature at which all the compressive residual stress introduced by the shot peening treatment can be removed. A ceramic product characterized by performing a heat treatment step of oxidizing SiC in the body to produce SiO ₂ and leaving a compressive residual stress of 250 MPa or more in a compressive residual stress introduction layer in a surface layer portion of the ceramic sintered body Production method.   4. The ceramic sintered body is machined before the heat treatment step, and the heat treatment step is performed after the shot peening treatment and the machining are completed. Manufacturing method of ceramic products.   In the shot peening treatment, a fine particle projection material having a Vickers hardness (HV) of 50 to 80% of the hardness of the ceramic sintered body and a particle size of 100 to 400 μm is projected onto the ceramic material at a shot pressure of 0.1 to 0.3 MPa. The method for producing a ceramic product according to claim 1, wherein:   The method for producing a ceramic product according to any one of claims 1 to 5, wherein a particle diameter of the fine particle projection material used in the shot peening treatment is 100 to 200 µm.   The production of the ceramic product according to any one of claims 1 to 6, wherein the shot pressure for projecting the fine particle projection material onto the ceramic sintered body in the shot peening treatment is 0.1 to 0.2 MPa. Method.   The method for manufacturing a ceramic product according to any one of claims 1 to 7, wherein the heat treatment step is performed in the air.   The method for manufacturing a ceramic product according to any one of claims 1 to 8, wherein the heat treatment step is performed in a state where bending stress is applied to the ceramic sintered body. A ceramic product manufactured by the method for manufacturing a ceramic product according to claim 1,
It has a ceramic sintered body made of a Si ₃ N ₄ / SiC composite material containing 10 to ₃₀ wt% of SiC fine particles, and in the surface layer portion in the range of ₃₀ to 50 μm in the depth direction from the surface of the ceramic sintered body, In a crack-like groove formed so as to have a compressive residual stress introduction layer remaining at a compressive residual stress of 250 MPa or more, and to extend from the surface of the compressive residual stress introduction layer to the inside of the ceramic sintered body A ceramic product comprising a filling joint portion made of SiO ₂ to be filled and joining portions located on both sides of the ceramic sintered body via the groove.

Images