JP2007039331A - Method of manufacturing silicon nitride sintered compact, method of manufacturing chemical resistant member using the same and method of manufacturing bearing member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a silicon nitride sintered compact having excellent chemical resistance (anti-corrosive property) against a chemical agent of acid, alkali or the like without impairing high strength, high abrasion resistance, high heat resistance and the like which are intrinsic characteristics of the silicon nitride sintered compact, to provide a method for manufacturing a chemical resistant member using the silicon nitride sintered compact, and to provide a method of manufacturing a bearing member. <P>SOLUTION: The method of manufacturing the silicon nitride sintered compact is carried out by preparing a ceramic mixture comprising 0.5-6 wt.% MgO-Al<SB>2</SB>O<SB>3</SB>spinel structure, 0.1-20 wt.% silicon carbide, ≤1 wt.% silicon oxide, 0.5-3 wt.% aluminum oxide and the balance substantially silicon nitride and forming and firing the resultant ceramic mixture. The resultant silicon nitride sintered compact is used as the chemical resistant member or the bearing members 1, 2, 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a silicon nitride sintered body, a method for producing a chemical resistant member using the same, and a method for producing a bearing member. In addition to excellent mechanical strength and wear resistance, the present invention relates to chemical resistance. Further, the present invention relates to a method for manufacturing a silicon nitride sintered body that is excellent, a method for manufacturing a chemical resistant member using the same, and a method for manufacturing a bearing member.

  Ceramic sintered body mainly composed of silicon nitride has excellent heat resistance and low thermal expansion coefficient, so it has various characteristics such as excellent thermal shock resistance. As high-temperature structural materials, application to engine parts, steelmaking machine parts, and the like has been attempted. Moreover, since it is excellent also in abrasion resistance, practical use as a sliding member, such as a bearing, or a cutting tool is also achieved.

Usually, silicon nitride is a hard-to-sinter ceramic material, so a rare earth oxide or aluminum oxide is added to the raw material powder as a sintering aid to improve the sinterability, and it is dense and has high strength. A ceramic sintered body is obtained. For example, the sintered composition of silicon nitride ceramics includes Si ₃ N ₄ —Y ₂ O ₃ —Al ₂ O ₃ , Si ₃ N ₄ —Y ₂ O ₃ —Al ₂ O ₃ —AlN, and Si _3. An oxide system such as N ₄ —Y ₂ O ₃ —Al ₂ O ₃ —Ti, Mg, Zr or the like is known (for example, see Patent Document 1).

The silicon nitride sintered body formed by adding rare earth element oxides such as yttrium oxide and aluminum oxide in the above sintered composition improves sinterability, promotes densification, and has excellent mechanical strength characteristics. It will be. Further, it has been devised to improve mechanical properties and wear resistance at high temperatures by adding a combination of a plurality of types of compounds such as aluminum nitride and titanium oxide.
Japanese Patent Laid-Open No. 6-219837

  However, the silicon nitride sintered body having the above composition has insufficient corrosion resistance to chemicals such as acid and alkali, and when employed as a structural material used in an environment where chemicals are mixed, There was a problem that predetermined durability and reliability could not be obtained. On the other hand, as a material excellent in chemical resistance, a sintered body using β-sialon as a raw material is also widely used. However, since the mechanical properties are insufficient, there is a drawback that the application range is limited. It was.

  For example, in recent years, there has been an increasing demand for bearing members, heat-resistant members, and wear-resistant members that can be used in an environment where a large amount of chemical substances are present. Since it is difficult to deal with alloys and heat-resistant cemented carbides, it is strongly desired to develop ceramic members that are not only superior in heat resistance and wear resistance but also in chemical resistance (corrosion resistance). ing. In particular, the demand for bearings that can be used in an environment where chemicals are present is increasing, but conventional metal rolling bearings have insufficient durability. Therefore, attempts have been made to apply ceramic materials that are superior to metal materials in basic required properties such as chemical resistance and heat resistance as bearing components, but ceramics that satisfy all the required properties of bearing materials. The material has not been realized yet.

  The present invention has been made to cope with such problems, and without damaging the original characteristics of the sintered silicon nitride, such as high strength, wear resistance, heat resistance, and the like, and further chemicals such as acids and alkalis. For the purpose of providing a method for producing a silicon nitride sintered body exhibiting excellent chemical resistance (corrosion resistance) against chemicals, a method for producing a chemical resistant member using the same, and a method for producing a bearing member Yes.

  In order to achieve the above object, the present inventors paid attention to the type and amount of the additive aid, added various compounds to the silicon nitride raw material powder to prepare sintered bodies, and corroded each sintered body. By comparing and evaluating the characteristics of the sintered body after exposure to the atmosphere, the effect of the type and amount of the additive added on the corrosion resistance of the sintered body was confirmed.

As a result, silicon nitride is added as additive aids with MgO.Al ₂ O ₃ spinel structure, silicon carbide, and optionally silicon oxide, and oxides and carbides of Ti, Hf and W. It has been found that a silicon nitride sintered body having excellent chemical resistance and little deterioration in strength can be obtained by blending an appropriate amount into the raw material.

The present invention has been made based on the above findings. That is, in the method for producing a silicon nitride sintered body according to the present invention, the MgO · Al ₂ O ₃ spinel structure is 0.5 to 6% by weight, silicon carbide is 0.1 to 20% by weight, and silicon oxide is used. A ceramic mixture comprising 1% by weight or less and 0.5 to 3% by weight of aluminum oxide, the balance being substantially composed of silicon nitride is prepared, and the resulting ceramic mixture is molded and fired. To do.

  In the method for producing a silicon nitride sintered body, the ceramic mixture may further contain at least one compound selected from titanium, hafnium, tungsten oxides and carbides in a range of 0.1 to 4% by weight. It is preferable to contain.

  Further, in the method for producing a silicon nitride sintered body, it is preferable that the ceramic mixture contains the silicon oxide in a range of 0.2 to 0.6% by weight.

  In the method for producing a silicon nitride sintered body, the ceramic mixture preferably contains the aluminum oxide in a range of 0.5 to 2% by weight.

  Furthermore, in the method for producing a silicon nitride sintered body, it is preferable that the ceramic mixture contains the silicon carbide in an amount of 1 to 10% by weight.

In the method for manufacturing a silicon nitride sintered body, it is preferable that the ceramic mixture contains the MgO · Al ₂ O ₃ spinel structure in an amount of 2 to 5% by weight.

  Further, in the method for producing a silicon nitride sintered body, when preparing the ceramic mixture, the ceramic mixture is mixed with a ball mill using an aluminum oxide ball as a grinding medium, and the aluminum oxide ball is converted into the ceramic mixture. The amount of aluminum oxide to be mixed is preferably 3% by weight or less.

  The method for producing a chemical resistant member of the present invention is characterized in that the silicon nitride sintered body produced by the method for producing a silicon nitride sintered body is processed into a predetermined shape to form a chemical resistant member. To do.

  Furthermore, the bearing member manufacturing method of the present invention is characterized in that the silicon nitride sintered body manufactured by the method for manufacturing a silicon nitride sintered body is processed into a predetermined shape to form a bearing member.

  The silicon nitride sintered body obtained according to the present invention contains 0.1 to 1.5% by weight of magnesium, 0.1 to 3% by weight of aluminum, 0.01 to 6% by weight of carbon, and oxygen as constituent elements. It is contained in the range of 0.2 to 5% by weight, and the balance is substantially made of silicon nitride. In the silicon nitride sintered body, the silicon nitride sintered body further contains at least one selected from titanium, hafnium, and tungsten as a constituent element in a range of 0.1 to 3.8% by weight. You may comprise.

In addition, the silicon nitride sintered body defined from the starting material composition is 0.5 to 6% by weight of MgO.Al ₂ O ₃ spinel structure, 0.1 to 20% by weight of silicon carbide, and 1 of silicon oxide. It is characterized by firing a ceramic mixture containing not more than wt% (including 0), aluminum oxide not more than 3 wt% (including 0), and the balance substantially consisting of silicon nitride. In addition to the MgO · Al ₂ O ₃ spinel structure, silicon carbide, silicon oxide, and aluminum oxide, at least selected from oxides and carbides of titanium, hafnium, tungsten as required. A ceramic mixture containing one compound in a range of 0.1 to 4% by weight is fired.

In the process of producing the silicon nitride sintered body targeted by the present invention, the MgO · Al ₂ O ₃ spinel structure added to the silicon nitride raw material powder not only functions as a sintering accelerator, but also a chemical. It forms a grain boundary phase exhibiting strong resistance to improving the chemical resistance of the sintered body. For this reason, it is added in the range of 0.5 to 6% by weight in the raw material powder. When the amount added is less than 0.5% by weight, densification of the sintered body becomes insufficient, and the original characteristics of the silicon nitride sintered body are impaired. On the other hand, when the addition amount exceeds 6% by weight, the chemical resistance starts to decrease conversely, so the amount is set within the above range, but a particularly preferable addition amount is in the range of 2 to 5% by weight.

  In addition, silicon carbide as another component added to the silicon nitride raw material powder used in the present invention not only exhibits an effect of improving chemical resistance, but also mechanical properties of the silicon nitride sintered body, particularly hardness. This contributes to an improvement in the strength of the sintered body. In addition, in a non-lubricated environment such as in chemicals, it is effective for reducing frictional resistance, and is added to the raw material powder in the range of 0.1 to 20% by weight. If the amount of silicon carbide added is less than 0.1% by weight, the effect of improving mechanical properties and the effect of reducing frictional resistance are insufficient, while if it exceeds 20% by weight, the sinterability is impaired. A more preferable addition amount is in the range of 1 to 10% by weight.

  Furthermore, silicon oxide as another component added to the silicon nitride raw material powder used in the present invention has an effect of strengthening the bond between silicon nitride particles and various additive aids and improving chemical resistance. 1% by weight or less (including 0) is added to the raw material powder. Silicon oxide is not necessarily added, but it is desirable to add it to obtain the above-described effects, and the amount added is 1% by weight or less. When the added amount exceeds 1% by weight, the sinterability is hindered. A more preferable range of the addition amount is 0.2 to 0.6% by weight.

  In addition, aluminum oxide as another component added to the silicon nitride raw material powder used in the present invention functions as a sintering accelerator for improving the sinterability, so that it is desirable to add more. However, if added in a large amount, the chemical resistance of the sintered body is impaired. And the range of the addition amount which functions as a sintering accelerator without reducing chemical resistance is 3% by weight or less, and more preferably in the range of 0.5 to 2% by weight.

In the ceramic mixture used in the present invention, in addition to the above-mentioned various auxiliary additives, at least one compound selected from oxides and carbides of Ti, Hf and W is added in the range of 0.1 to 4% by weight. Can be added. These compounds of Ti, Hf, and W act synergistically with the MgO.Al ₂ O ₃ spinel structure, function as a sintering accelerator that promotes densification, and have a high melting point after sintering. Thus, it shows a form in which it is dispersed as a single particle in the sintered body structure, and has the effect of improving the strength and wear resistance of the sintered body. The Ti, Hf, and W compounds are preferably added to the raw material powder in the range of 0.1 to 4% by weight. When the addition amount is less than 0.1% by weight, the effect of promoting the sinterability and improving the strength characteristics is small, whereas when it exceeds 4% by weight, the chemical resistance is lowered. In order to maintain the mechanical strength and chemical resistance of the sintered body, it is more preferable to add in the range of 1 to 2% by weight.

The content of each constituent element in the silicon nitride sintered body produced according to the present invention is specified for the same reason as the above-described addition amount definition of each additive component, and the Mg content is 0.1 weight. If the Al content is less than 0.1% or less than 0.1% by weight, good chemical resistance cannot be imparted and the density of the sintered body is reduced, while the Mg content is 1 If it exceeds 0.5% by weight or if the Al content exceeds 3% by weight, the chemical resistance decreases. These are basically contained at a ratio that can constitute the MgO.Al ₂ O ₃ spinel structure, but slightly change in the sintering process and the like. The content range of oxygen (O) conforms to the reason for the content of Mg and Al. Carbon (C) is added as silicon carbide, and if the C content is less than 0.01% by weight, the mechanical properties and chemical resistance cannot be sufficiently improved. When it exceeds 6% by weight, the density of the sintered body is lowered. The same applies to Ti, Hf, and W.

  The silicon nitride sintered body targeted by the present invention is produced, for example, by the following production method.

That is, at least selected from MgO · Al ₂ O ₃ spinel structure, silicon carbide, silicon oxide, aluminum oxide, and, if necessary, oxides and carbides of Ti, Hf, and W in the silicon nitride raw material powder A predetermined amount of one compound is added to prepare a raw material mixture. Next, the obtained raw material mixture is formed into a desired-shaped formed body (ceramic mixture formed body) by a general-purpose forming method such as a die press, and then this formed body is placed in an inert gas atmosphere such as nitrogen gas or argon gas. And sintering at a temperature of about 1700 to 1850 ° C. for a predetermined time. The sintering operation may be performed by atmospheric pressure sintering, or by applying other sintering methods such as hot pressing, atmospheric pressure sintering, hot isostatic pressing (HIP), etc. You may implement. In any sintering method, a dense silicon nitride sintered body with high mechanical strength and excellent chemical resistance (corrosion resistance) is obtained, especially in a usage environment where chemicals such as acid and alkali are mixed. It is done.

  According to the method for manufacturing a silicon nitride sintered body, the method for manufacturing a chemical resistant member using the same, and the method for manufacturing a bearing member according to the present invention, particles having chemical resistance in the sintered body structure, in particular, due to the spinel structure. Since the field phase is formed, the corrosion resistance can be improved, and the mechanical characteristics can be improved without impairing the original wear resistance of the silicon nitride sintered body. Therefore, it is a silicon nitride sintered body that is extremely useful as a high-strength wear-resistant and chemical-resistant member that replaces conventional corrosion-resistant and heat-resistant alloys and corrosion-resistant cemented carbides that constitute bearing parts and gas turbine parts. .

  Next, the present invention will be described more specifically with reference to the following examples.

[Example 1 and Comparative Examples 1-2]
An α-phase type silicon nitride powder having an average particle size of 0.7 μm, 89.5% by weight, an MgO · Al ₂ O ₃ spinel structure powder having an average particle size of 0.8 μm, and an average particle size of 0.5 μm A ball mill using a mixture of 3% by weight of silicon carbide powder, 0.5% by weight of silicon oxide powder having an average particle size of 0.7 μm and 3% by weight of aluminum oxide powder having an average particle size of 0.9 μm, using toluene as a solvent. Were mixed for 96 hours to prepare a uniform raw material mixture.

Next, a predetermined amount of an organic binder was added to the obtained raw material mixture and mixed uniformly, and then pressure-molded with a molding pressure of 1000 kgf / cm ² to prepare a 50 × 50 × 5 mm molded body. Next, after the obtained molded body was degreased in an air atmosphere at a temperature of 500 ° C., the degreased body was sintered at 1850 ° C. for 6 hours in a nitrogen gas atmosphere, and the silicon nitride firing according to Example 1 was performed. A ligation was prepared.

On the other hand, as a comparison with the present invention, in Example 1 above, MgO.Al ₂ O ₃ spinel structure powder was not added, and yttrium oxide powder having an average particle size of 0.9 μm was 2% by weight and the average particle size was 0. A silicon nitride sintered body according to Comparative Example 1 was prepared by mixing, molding and sintering under the same conditions as in Example 1 except that only 2% by weight of 9 μm aluminum oxide powder was added.

  Further, in Example 1 above, except that the amount of aluminum oxide added was set to an excessive amount of 6% by weight, mixing, molding, degreasing, and sintering were performed under the same conditions as Example 1, and nitriding according to Comparative Example 2 was performed. A silicon sintered body was prepared.

The silicon nitride sintered bodies according to Example 1 and Comparative Examples 1 and 2 thus obtained were measured for density, bending strength at room temperature (25 ° C.), and fracture toughness. Further, in order to evaluate chemical resistance, each sample was immersed in a 30% strength HCl solution and heat-treated at 90 ° C. for 100 hours, and weight loss and bending strength after the treatment were measured. The results are shown in Table 1. The constituent elements contained in the silicon nitride sintered body according to Example 1 were Mg 0.7% by weight, Al 1.8% by weight, O 2.7% by weight, C 1.0% by weight, Si 57. They were 2 wt%, N 36.6 wt%, and impurities (Fe, etc.) 0.01 wt%.

  As shown in the results of Table 1, the silicon nitride sintered body according to Example 1 has excellent mechanical properties such as bending strength and fracture toughness, and the properties after the immersion treatment are the same as those of Comparative Example 1. It has been found that the sintered body of the yttrium oxide-added system has less weight loss and is excellent in chemical resistance and also has excellent mechanical properties.

  The difference between the sintered bodies of Example 1 and Comparative Example 2 is that the amount of aluminum oxide contained in the raw material mixture prepared by mixing with a ball mill is different from 3% by weight and 6% by weight, respectively. Only. The mechanical properties such as bending strength and fracture toughness value of the sintered body according to Comparative Example 2 are comparable to those of the sintered body of Example 1. However, in the sintered body of Comparative Example 2, it was found that the bending strength after immersion in HCl clearly decreased.

  When a raw material mixture is prepared using a ball mill mixer using aluminum oxide balls as a grinding medium, a considerable amount of aluminum oxide components are inevitably mixed into the raw material mixture due to depletion of alumina balls. This has been confirmed by experiments by the present inventors. However, as is clear from the comparison results between Example 1 and Comparative Example 2 above, if the contamination amount of the aluminum oxide component from the ball mill mixer is 3% by weight or less, the strength characteristics and anti-resistance of the silicon nitride sintered body are reduced. It was also confirmed that there was little risk of reducing chemical properties.

[Examples 2-15, Comparative Examples 3-6]
The silicon nitride powder, the MgO.Al ₂ O ₃ spinel structure powder, the silicon carbide powder, the silicon oxide powder, the aluminum oxide powder, and the oxide or carbide powder of Ti, Hf, and W used in Example 1 The raw material mixtures were prepared by blending so that the composition ratio shown in FIG. Next, each obtained raw material mixture was molded, degreased, and sintered under the same conditions as in Example 1 to produce silicon nitride sintered bodies according to Examples 2 to 15, respectively.

On the other hand, as Comparative Examples 3 to 6, as shown in Table 2, an excessive addition of silicon carbide (Comparative Example 3) and an excessive addition of MgO.Al ₂ O ₃ spinel structure (Comparative Example 4) Then, an excessively added silicon oxide (Comparative Example 5) and an excessively added titanium oxide (Comparative Example 6) were respectively prepared, and the sintering operation was performed from the raw material mixing under the same conditions as in Example 1. The silicon nitride sintered bodies according to Comparative Examples 3 to 6 respectively corresponding to these were prepared.

  For each silicon nitride sintered body of Examples 2 to 15 and Comparative Examples 3 to 6 thus obtained, the density, bending strength, and hardness were measured under the same conditions as in Example 1, and immersion treatment was performed. The weight loss and bending strength of the sample were measured. The measurement results are shown in Table 3.

  As is apparent from the results shown in Table 3, a spinel structure, silicon carbide, aluminum oxide, silicon oxide as required, and an oxide or carbide of Ti, Hf, W were added in predetermined amounts. Each of the sintered bodies of Examples 2 to 15 exhibited high mechanical properties, and was confirmed to be excellent in chemical resistance with little decrease in weight and bending strength after the HCl immersion test.

  Further, the silicon nitride sintered body prepared as described above was actually applied to a chemical-resistant member of a bearing, and the durability including the chemical resistance of the bearing was evaluated. That is, a silicon nitride sintered body prepared according to the manufacturing method according to Example 12 was processed to manufacture a ceramic ball bearing (ball bearing) as shown in FIG. This ball bearing is constructed by interposing a spherical rolling element (silicon nitride ball) 3 between a cylindrical inner ring 1 and an outer ring 2 made of the silicon nitride sintered body.

  On the other hand, as a comparative example, a conventional steel (SUJ2) ball bearing having the same dimensions was prepared, and a continuous rotation test was performed in a grease lubrication environment where hydrochloric acid mist was mixed together with the ceramic ball bearing. As a result, ceramic ball bearings with better heat resistance and corrosion resistance can maintain hardness even at high temperatures and do not cause seizure compared to conventional steel ball bearings. It was found that the film could be stretched, and it was confirmed that an excellent effect could be exhibited.

Sectional drawing which shows the structure of the ball bearing (ball bearing) formed with the silicon nitride sintered compact concerning this invention.

Explanation of symbols

1 Inner ring 2 Outer ring 3 Rolling element (silicon nitride ball)

Claims (9)

0.5 to 6% by weight of MgO.Al ₂ O ₃ spinel structure, 0.1 to 20% by weight of silicon carbide, 1% by weight or less of silicon oxide, and 0.5 to 3% by weight of aluminum oxide A method for producing a silicon nitride sintered body, comprising preparing a ceramic mixture substantially comprising silicon nitride as a balance, and forming the obtained ceramic mixture and then firing it. 2. The method of manufacturing a silicon nitride sintered body according to claim 1, further comprising 0.1 to 4 wt% of at least one compound selected from titanium, hafnium, an oxide of tungsten, and a carbide in the ceramic mixture. A method for producing a silicon nitride sintered body, wherein the silicon nitride sintered body is contained in a range. 3. The method of manufacturing a silicon nitride sintered body according to claim 1 or 2, wherein the ceramic mixture contains the silicon oxide in a range of 0.2 to 0.6% by weight. A method for producing a knot. 3. The method of manufacturing a silicon nitride sintered body according to claim 1, wherein the ceramic mixture contains the aluminum oxide in a range of 0.5 to 2% by weight. Production method. 3. The method of manufacturing a silicon nitride sintered body according to claim 1 or 2, wherein the ceramic mixture contains the silicon carbide in an amount of 1 to 10% by weight. Method. 3. The method of manufacturing a silicon nitride sintered body according to claim 1, wherein the ceramic mixture contains the MgO.Al ₂ O ₃ spinel structure in a range of 2 to 5% by weight. A method for producing a silicon sintered body. 7. The method of manufacturing a silicon nitride sintered body according to claim 1, wherein the ceramic mixture is prepared by mixing the ceramic mixture with a ball mill using aluminum oxide balls as a grinding medium. A method for producing a silicon nitride sintered body, characterized in that the amount of aluminum oxide mixed into the ceramic mixture from an aluminum oxide ball is 3% by weight or less. A chemical-resistant member formed by processing the silicon nitride sintered body produced by the method for producing a silicon nitride sintered body according to any one of claims 1 to 7 into a predetermined shape. Manufacturing method of member. A method for manufacturing a bearing member, comprising forming a bearing member by processing the silicon nitride sintered body manufactured by the method for manufacturing a silicon nitride sintered body according to any one of claims 1 to 7 into a predetermined shape. .

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