JPH11147774A - Ceramic material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of the strength of a ceramic product. SOLUTION: A ceramic product having a low strength is easily removed by subjecting a ceramic product to an overload test comprising adding a larger load than a practically used load to a sintered ceramic product in the same state as a practical using state and further preferably to a thermal treatment carried out in the atmosphere. The fine detects of the surface of the ceramic product are repaired with a new product produced from a sintering auxiliary, silicon nitride and silicon carbide (in a case of a composite material). Thereby, the reliability of the strength of the ceramic product can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various structural ceramic materials and methods for producing the same. For example, oxide ceramic materials include alumina and mullite, and non-oxide ceramic materials include silicon nitride and aluminum nitride. There are silicon carbide, sialon, and the like. This application includes various parts of automobiles, gas turbines, fuel cells, furnaces, springs, and the like, and particularly relates to a silicon nitride ceramic material, a composite material mainly composed of silicon nitride, and a method for producing the same.

[0002]

2. Description of the Related Art Generally, a ceramic material (product) is manufactured by adding a sintering aid to a raw material powder, mixing and adjusting the mixture, and adding and mixing a binder for imparting plasticity and shape retention. , Forming step and sintering step. Thereafter, machining is performed to improve the shape accuracy and the properties (roughness, surface altered layer) of the product surface.

[0003]

However, since the ceramic material has low toughness, the strength is reduced even with minute defects. In addition, cracks often occur during machining such as grinding, and cracks (defects) often occur for some reason in the manufacturing process, and there is a problem that the reliability of the strength of the completed ceramic product is low. It is very difficult to find these fine defects by nondestructive inspection. The inventor of the present invention has considered that the reliability of the finished ceramic product can be remarkably improved if the ceramic product having these defects can be removed before use and the surface defect can be cured (self-healing).

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to improve the reliability of strength of a ceramic product.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention relates to a method of manufacturing a semiconductor device, comprising the steps of: Provided are a method for producing a ceramic material, which is characterized by applying the above load and further performing a heat treatment, and a ceramic material produced by this method.

[0006]

Preferred embodiments of the present invention will be described below.

[0007] After sintering or machining, which is the final stage of the manufacturing process of a ceramic product, a product (defected product) that breaks at a low stress by applying a stress equal to or higher than the stress used by the product is obtained. Removal and heat treatment cure defects on the surface of the product and improve the reliability of strength. As the main process, if no machining is performed, material adjustment → molding → degreasing → sintering → overload test → heat treatment → product or material adjustment → molding → degreasing → sintering → heat treatment → overload test → product When processing, adjust raw materials → molding → degreasing → sintering → machining → overload test →
Heat treatment → product or raw material adjustment → molding → degreasing → sintering → machining → heat treatment → overload test → product. The order of the steps of the overload test and the heat treatment may be reversed. In the overload test, under the same load condition as the use condition of the product, a stress equal to or higher than the stress used is applied, and a product (a product having a defect) that is broken by low stress is removed. Here, the same load state as the use state of the product means that a load is applied in the same direction as the load applied to the product, and is not limited to a state in which the load is applied in the same mounting state as the product. . As the heat treatment temperature, a range of 800 ° C. to 1400 ° C. is suitable, though appropriate conditions vary depending on the material. Then, the heat treatment is performed in the air, in a vacuum, or in an inert gas. In particular, performing in the atmosphere has a large effect of improving strength.

[0008]

EXAMPLES Example 1 Silicon nitride (Si ₃ N ₄ ) was used as a main raw material. Sintering aids added to the main raw materials include Mg, Al, Be, Z
oxide or nitride such as r, Y ₂ O ₃ , CeO, Er
Rare earth oxides such as ₂ O ₃ and La ₂ O ₃ are exemplified. In this example, 5 wt% of Y ₂ O ₃ and 3 wt% of Al ₂ O ₃ were added to the silicon nitride powder. These powders were wet-mixed with distilled water using a ball mill, and then dried to obtain a mixed powder. To this mixed powder, methylcellulose and a plasticizer were used as a binder, and distilled water was added as a solvent, followed by uniform kneading.

Thereafter, the kneaded material was formed into a wire using an extruder. Further, the wire was subjected to a binder removal treatment (degreasing) and sintered. Sintering suppresses the decomposition reaction of Si ₃ N ₄ and obtains a high-density wire with good surface properties.
_{In two} atmospheres, the N ₂ gas pressure was set to 0.93 MPa, and 185
The pressure sintering was performed under the conditions of 0 ° C. × 4 hours.

The wire has a diameter of 3.6 mm and a length of 4 mm.
0.0 mm. No machining such as grinding or polishing was performed. The overload test was performed by a four-point bending test at room temperature with a stress of 675 MPa and a crosshead speed of 0.5 mm / min. The heat treatment is carried out at a temperature of 8 in the atmosphere.
The test was performed at a temperature of 00 ° C. to 1400 ° C., a holding time of 1 hour to 10 hours, and a heating rate of 10 ° C./min. The strength of the wire was evaluated by a four-point bending test at room temperature under the conditions of a long span of 30 mm, a short span of 10 mm, and a crosshead speed of 0.5 mm / min.

Table 1 shows the evaluation results of the four-point bending strength and the Weibull value of a wire made of a silicon nitride ceramic material heat-treated in the air after sintering, with the sintering aid being Y ₂ O ₃ + Al ₂ O _3. . Specimen A was heat-treated in air without sintering after sintering, and Specimen B was subjected to overloading after sintering and had a low strength (relative to the inside and surface). After the removal of a material having a large defect), it is further heat-treated in the air.

[0012]

[Table 1]

As shown in Table 1, the heat treatment improved the strength at all heat treatment temperatures from 800 ° C. to 1400 ° C. as compared with those not heat-treated. Further, since the m-value calculated by the Weibull analysis is high, the variation in strength is small, and the reliability is improved. By performing an overload test, a material having a lower strength could be removed in advance, and the strength and reliability were further improved.

The improvement in strength is due to the fact that the residual stress is removed by the heat treatment and a new product is formed on the surface, covering and healing the defect (crack). The new product has been produced from primary raw material and sintering aid products, Si ₂ from the X-ray diffraction
It was confirmed that Y ₂ O ₇ and SiO ₂ were healing substances.

Example 2 5 wt% of Y ₂ O _{3 based on} silicon nitride (Si ₃ N ₄ ) powder
And 3 wt% of Al ₂ O ₃ . In addition, silicon nitride (Si
_When 3N ₄ ) is used, other than the above, sintering aids added to the raw material include oxides or nitrides such as Mg, Al, Be, and Zr, CeO, Er ₂ O ₃ , and La ₂ O ₃ . Rare earth oxides and the like. These powders were wet-mixed with distilled water using a ball mill, and then dried to obtain a mixed powder. To this mixed powder, methylcellulose and a plasticizer were used as a binder, and distilled water was added as a solvent, followed by uniform kneading.

Thereafter, the kneaded material was formed into a wire using an extruder. The wire was coiled into a coil spring shape, and then the coil spring was debindered (degreased) and sintered. In the sintering, in order to suppress the decomposition reaction of Si ₃ N ₄ and obtain a high-density coil spring having good surface properties, the N ₂ gas pressure is set to 0.93 MPa in an N ₂ atmosphere.
The pressure sintering was performed at 1850 ° C. × 4 hours. The coil spring has an outer diameter of φ20.65 mm and a wire diameter of φ2.4.
5 mm, free length: 54.65 mm, total number of turns: 13, effective number of turns: 11.5. In the overload test, at room temperature, the stress was 42.5 kgf / mm ² and the crosshead speed was 20 m.
m / min. The heat treatment is performed in the atmosphere at a temperature of 1000 ° C. to 1300 ° C. and a holding time of 1 hour to 1 hour.
The operation was performed at a heating rate of 10 ° C./min for 0 hour. Actually, the coil spring may be subjected to the heat treatment while applying a stress. For evaluation of the strength of the coil spring, a compression test was performed at room temperature under the condition of a crosshead speed of 20 mm / min, and a destructive test was performed.

Table 2 shows the results of a fracture strength test of a coil spring made of a silicon nitride ceramic material heat-treated in the air after sintering, with the sintering aid being Y ₂ O ₃ + Al ₂ O ₃ . Sample A was heat-treated in air without sintering after sintering. Sample B was subjected to overload after sintering, and after removing low-strength materials, Heat treated inside.

[0018]

[Table 2]

As shown in Table 2, the average strength is compared.
At all the heat treatment temperatures, the strength was improved as compared with those not heat-treated. However, when a large defect (crack) is present inside the coil spring, a large improvement in strength cannot be expected even if heat treatment is performed.
Breaks down under a load of 0.0 kgf / mm ² or less. Therefore,
By performing an overload test (42.5 kgf / mm ² ) and removing such a low-strength material in advance, the strength is further improved by a subsequent heat treatment, the strength variation is reduced, and the reliability is improved.

Although the overload test is performed at room temperature in the above embodiment, the overload test may be performed in a heated state according to the use environment of the product.

[0021]

As is apparent from the above description, according to the ceramic material and the method of manufacturing the same according to the present invention, the sintering is performed under the same condition as the actual use condition, by applying a load more than the load used. By a load test and a heat treatment preferably performed in the air, low-strength materials are easily removed, and surface defects are cured by a new product produced by heat treatment from a sintering aid or a ceramic main material ( Self-healing), thereby improving the reliability of the strength of the ceramic product.

Continuation of the front page (72) Inventor Yasuyoshi Kobayashi 3-10-10 Fukuura, Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture Within Nihon Hojo Co., Ltd. (72) Inventor Autumn 29 Fujigazawa House 7-401 (72) Inventor Tomoyuki Sone 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki Prefecture

Claims (11)

[Claims] 1. A ceramic material characterized in that after sintering, in a state similar to an actual use state, a load greater than an actually applied load is applied and a heat treatment is performed. 2. The ceramic material according to claim 1, wherein the ceramic material is machined after sintering, and then subjected to the load and heat treatment. 3. The ceramic material according to claim 1, wherein the heat treatment is performed in a state where a stress is applied. 4. The heat treatment is performed at 800 ° C. to 1400 ° C.
The ceramic material according to any one of claims 1 to 3, wherein the ceramic material is formed at a temperature of between: 5. The ceramic material according to claim 1, wherein the heat treatment is performed in the atmosphere. 6. The ceramic material is made of a silicon nitride ceramic material, and one or more selected from oxide ceramics, nitride ceramics, and rare earth oxides are added as a sintering aid. The ceramic material according to any one of claims 1 to 5, wherein: 7. A method for producing a ceramic material, comprising: a step of applying a load equal to or more than an actually applied load in a state similar to an actual use state after sintering; and a step of performing a heat treatment. 8. The method for producing a ceramic material according to claim 7, further comprising a step of performing machining after sintering, and thereafter further applying the load and heat-treating. 9. The heat treatment is performed at 800 ° C. to 1400 ° C.
9. The method for producing a ceramic material according to claim 7, wherein the method is carried out at a temperature between the steps (a) and (b). 10. The method according to claim 7, wherein the heat treatment is performed in the atmosphere. 11. A ceramic material comprising a silicon nitride ceramic material, wherein one or more selected from an oxide ceramic, a nitride ceramic and a rare earth oxide are added as a sintering aid to sinter a raw material. 11. The method for manufacturing a ceramic material according to claim 7, wherein each of the subsequent processes is performed.