JPH0920563A - Sintered silicon nitride - Google Patents

Abstract

PURPOSE: To obtain a sintered silicon nitride exhibiting excellent chemical resistance (corrosion resistance) to chemicals such as acid and alkali without deteriorating characteristic high strength, abrasion resistance, heat-resistance, etc., of sintered silicon nitride. CONSTITUTION: This sintered silicon nitride contains 0.1-1.5wt.% of magnesium, 0.1-3wt.% of aluminum, 0.01-6wt.% of carbon and 0.2-5wt.% of oxygen as constituent elements and the remaining part essentially composed of silicon nitride. The sintered silicon nitride can be produced by burning a ceramic mixture composed of 0.5-6wt.% of an MgO-Al2 O3 spinel structure material, 0.1-20wt.% of silicon carbide, <=1wt.% of silicon oxide, <=3wt.% of aluminum oxide and the remaining part essentially composed of silicon nitride. The sintered silicon nitride can be used as a chemical resistance part or bearing parts 1, 2, 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride sintered body, and more particularly to a silicon nitride sintered body having excellent chemical resistance in addition to excellent mechanical strength and wear resistance.

[0002]

2. Description of the Related Art Sintered ceramics containing silicon nitride as a main component have excellent heat resistance and a small coefficient of thermal expansion, and thus have various properties such as excellent thermal shock resistance. As a high-temperature structural material to replace the heat-resistant alloy of
Application to engine parts, mechanical parts for steelmaking, and the like has been attempted. Further, since it is also excellent in wear resistance, it is being put to practical use as a sliding member such as a bearing and a cutting tool.

Since silicon nitride is usually a ceramic material which is difficult to sinter, a predetermined amount of rare earth oxide, aluminum oxide or the like as a sintering aid is added to the raw material powder to improve the sinterability and to make it dense. We have obtained a high-strength ceramic sintered body.
For example, the sintering composition of the silicon nitride Motokei _{ceramics, Si 3 N 4 -Y 2 O} 3 -Al 2 O 3 system, Si ₃ N _{4
-Y 2 O 3 -Al 2 O 3} -AlN system, Si ₃ N ₄ -Y ₂
Oxide systems such as O ₃ —Al ₂ O ₃ —Ti, Mg, and Zr are known.

A silicon nitride sintered body formed by adding an oxide of a rare earth element such as yttrium oxide or aluminum oxide in the above-mentioned sintering composition has improved sinterability, promotes densification, and has mechanical strength characteristics. Will also be excellent. Further, it is devised to improve mechanical properties and wear resistance at high temperature by adding a combination of plural kinds of compounds such as aluminum nitride and titanium oxide.

[0005]

However, any of the silicon nitride sintered bodies having the above composition has insufficient corrosion resistance to chemicals such as acids and alkalis, and is used in an environment in which chemicals are mixed. When adopted as a structural material, there is a problem that predetermined durability and reliability cannot be obtained. On the other hand, as a material having excellent chemical resistance, a sintered body made of β-sialon is widely used, but it has a drawback that its application range is limited due to insufficient mechanical properties. 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 environments where a large amount of chemical substances are present, and they have been conventionally used for such applications. Corrosion-resistant / heat-resistant alloys and heat-resistant cemented carbides are difficult to handle, so the emergence of ceramic members not only superior in heat resistance and wear resistance to metals, but also in chemical resistance (corrosion resistance) Strongly desired. In particular, there is an increasing demand for bearings that can be used in environments where chemicals are present, but conventional metal rolling bearings have insufficient durability. Therefore, it has been attempted to apply a ceramic material, which has basic characteristics such as chemical resistance and heat resistance, which are superior to those of metal materials, as a bearing constituent material. Ceramics satisfying all the required characteristics of the bearing material. The material has not been realized yet.

The present invention has been made in order to solve such a problem, and further, without impairing the high strength, wear resistance, heat resistance, etc., which are the original characteristics of the silicon nitride sintered body, the acid and alkali It is an object of the present invention to provide a silicon nitride sintered body that exhibits excellent chemical resistance (corrosion resistance) against chemicals such as.

[0008]

Means and Actions for Solving the Problems In order to achieve the above-mentioned object, the present inventors have paid attention to the kind and amount of the additive aid, and added various compounds to the raw material powder of silicon nitride and sintered it. The effects of the types and amounts of the above-mentioned additives on the corrosion resistance of the sintered body were confirmed by comparing the sintered body characteristics after preparing the sintered body and exposing each sintered body to a corrosive atmosphere. did.

As a result, the MgO.Al ₂ O ₃ spinel structure, silicon carbide and, if necessary, silicon oxide, T
By mixing at least one of i, Hf and W oxides, and at least one of carbides into the silicon nitride raw material as an additive aid, a silicon nitride sintered body having excellent chemical resistance and little strength deterioration can be obtained. I found that

The present invention was made based on the above findings, and the silicon nitride sintered body of the present invention has the following constituent elements:
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 0.2 to 5% by weight of oxygen, with the balance substantially. It is characterized by being made of silicon nitride. Further, in the above silicon nitride sintered body, the silicon nitride sintered body further contains 0.1 to 3.8% by weight of at least one selected from titanium, hafnium, and tungsten as its constituent elements.
You may comprise so that it may be included in the range of.

The silicon nitride sintered body according to the present invention defined by the starting material composition is 0.5 to 6% by weight of MgO.Al ₂ O ₃ spinel structure and 0.1 to 20% by weight of silicon carbide. A ceramic mixture containing 1% by weight or less (including 0) of silicon oxide, 3% by weight or less (including 0) of aluminum oxide, and the balance substantially consisting of silicon nitride. It has a feature. In addition, the above MgO / Al
_{In addition to the 2} O ₃ spinel structure, silicon carbide, silicon oxide, and aluminum oxide, at least one compound selected from titanium, hafnium, tungsten oxides and carbides may be added as necessary. .1 to 4
It is characterized in that it is obtained by firing a ceramics mixture containing it in the range of wt%.

MgO added to the silicon nitride raw material powder in the step of producing the silicon nitride sintered body according to the present invention.
The Al ₂ O ₃ spinel structure not only functions as a sintering accelerator, but also improves the chemical resistance of the sintered body by forming a grain boundary phase that is particularly resistant to chemicals. is there. Therefore, it is added to the raw material powder in the range of 0.5 to 6% by weight. If the amount added is less than 0.5% by weight, the densification of the sintered body will be insufficient and the original properties of the silicon nitride sintered body will be impaired. On the other hand, if the amount added exceeds 6% by weight, the chemical resistance will start to decrease, and therefore the above range is set, but the particularly preferable amount added is within the range of 2 to 5% by weight.

Further, silicon carbide as another component added to the silicon nitride raw material powder in the present invention not only exerts the effect of enhancing chemical resistance, but also the mechanical properties of the silicon nitride sintered body, particularly It contributes to the improvement of hardness and achieves high rigidity of the sintered body. Further, in a non-lubricated environment such as in chemicals, it also has an effect of reducing frictional resistance, and is added to the raw material powder in an amount of 0.1 to 20% by weight. When 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 preferred amount is in the range of 1 to 10% by weight.

Furthermore, in the present invention, silicon oxide as another component added to the silicon nitride raw material powder has the effect of strengthening the bond between the silicon nitride particles and various additive aids and enhancing the chemical resistance. Then, 1% by weight or less (including 0) is added to the raw material powder. Silicon oxide is not necessarily required to be added, but it is desirable to add it in order to obtain the above effects, and the addition amount at that time is 1% by weight.
The following is assumed. If the amount added exceeds 1% by weight, the sinterability will be impaired. A more preferable range of addition is 0.2 to 0.6% by weight.

Further, in the present invention, aluminum oxide as another component added to the silicon nitride raw material powder 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 will be impaired. And the range of the amount of addition to function as a sintering accelerator without lowering the chemical resistance is 3% by weight or less, more preferably 0.5 to 2% by weight.

In the ceramic mixture used in the present invention, in addition to the above various additive aids, Ti and Hf are further added.
And at least one compound selected from the oxides and carbides of W can be added in the range of 0.1 to 4% by weight. These compounds of Ti, Hf and W are MgO
-Al ₂ O ₃ spinel structure acts synergistically to function as a sintering accelerator that promotes densification, and also becomes a high melting point compound after sintering, and as a particle, a sintered body structure It has the effect of improving the strength and wear resistance of the sintered body. The compounds of Ti, Hf and W are preferably added to the raw material powder in a range of 0.1 to 4% by weight. When the addition amount is less than 0.1% by weight, the effect of promoting sinterability and improving strength characteristics is small,
On the other hand, if it exceeds 4% by weight, the chemical resistance is lowered.
To maintain the mechanical strength and chemical resistance of the sintered body, 1
More preferably, it is added in the range of 2 wt%.

The content of each constituent element in the silicon nitride sintered body of the present invention is specified for the same reason as the above-mentioned addition amount specification of each additive component, and the content of Mg is 0.1% by weight. % Or the Al content is less than 0.1% by weight, good chemical resistance cannot be imparted, and the density of the sintered body decreases, while Mg
Content of more than 1.5% by weight, Al content of 3
On the other hand, if it exceeds the weight%, the chemical resistance is lowered. These are contained basically in such a ratio that they can form a MgO.Al ₂ O ₃ spinel structure, but they are somewhat changed in the sintering process or the like. The oxygen (O) content range is based on the reason for the Mg and Al content. Further, carbon (C) is added as silicon carbide, and if the content of C is less than 0.01% by weight, mechanical properties and chemical resistance cannot be sufficiently enhanced, while If 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 according to the present invention is manufactured, for example, by the following manufacturing method.

That is, MgO.
Al ₂ O ₃ spinel structure, silicon carbide, silicon oxide,
Aluminum oxide and, if necessary, Ti, H
at least 1 selected from oxides and carbides of f and W
A predetermined amount of the seed compound is added to prepare a raw material mixture. Next, after the obtained raw material mixture is formed into a formed body (ceramics mixture formed body) having a desired shape by a general-purpose forming method such as a die press, the formed body is placed in an atmosphere of an inert gas such as nitrogen gas or argon gas. Then, sintering is performed at a temperature of about 1700 to 1850 ° C. for a predetermined time. The sintering operation is
It may be carried out by the normal pressure sintering method or by applying other sintering methods such as a hot pressing method, an atmosphere pressure sintering method, a hot isostatic pressing method (HIP) and the like. Dense and high mechanical strength is obtained by any of the sintering methods, and a silicon nitride sintered body with excellent chemical resistance (corrosion resistance) is obtained, especially in a usage environment where chemicals such as acids and alkalis are mixed. To be

[0020]

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

Example 1 and Comparative Examples 1 and 2 89.5% by weight of α-phase silicon nitride powder having an average particle size of 0.7 μm and MgO.Al ₂ O ₃ spinel structure powder having an average particle size of 0.8 μm. 4% by weight, 3% by weight of silicon carbide powder having an average particle size of 0.5 μm, 0.5% by weight of silicon oxide powder having an average particle size of 0.7 μm, and aluminum oxide powder 3 having an average particle size of 0.9 μm The mixture with the weight% was mixed with toluene as a solvent in a ball mill 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 uniformly mixed, and then 1000 kgf
/ Cm pressure and pressure molded at ² of molding pressure, 50 × 50 × 5mm
Was formed. Then, the obtained molded body is heated to a temperature of 5
After degreasing in an air atmosphere of 00 ° C., the degreased body was subjected to normal pressure sintering in a nitrogen gas atmosphere at 1850 ° C. for 6 hours to prepare a silicon nitride sintered body according to Example 1.

On the other hand, as a comparison with the present invention, in Example 1 described above, MgO.Al ₂ O ₃ spinel structure powder was not added, and 2% by weight of yttrium oxide powder having an average particle size of 0.9 μm was added. 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 aluminum oxide powder having a diameter of 0.9 μm was added.

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

Example 1 and Comparative Examples 1-2 thus obtained
For each silicon nitride sintered body according to
The bending strength and fracture toughness value in (° C.) Were measured. To evaluate chemical resistance, each sample was 30
%, And heat-treated at 90 ° C. for 100 hours, and the weight loss and flexural strength after the treatment were measured. Table 1 shows the results. 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 wt%, Si 57.2 wt%, N 36.6
% By weight, and 0.01% by weight of impurities (Fe, etc.).

[0026]

[Table 1]

As shown by the results in 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 immersion are also compared. It was found that the yttrium oxide-added sintered body of Example 1 had less weight loss, was excellent in chemical resistance, and was also excellent in mechanical properties.

The difference between the sintered bodies of Example 1 and Comparative Example 2 is that the amounts of aluminum oxide contained in the raw material mixture prepared by mixing with a ball mill are 3% by weight and 6% by weight, respectively. Is the only difference. 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 dipping in HCl obviously decreased.

When a raw material mixture is prepared by using a ball mill mixer using aluminum oxide balls as a grinding medium, a considerable amount of aluminum oxide component is unavoidable due to the wear of the alumina balls. It has been confirmed by experiments by the present inventors that they are mixed in. However, as is clear from the comparison result between Example 1 and Comparative Example 2, if the contamination amount of the aluminum oxide component mixed from the ball mill mixer is 3% by weight or less, the strength characteristics and the resistance of the silicon nitride sintered body are improved. It was also confirmed that there is little risk of lowering the chemical properties.

Examples 2 to 15, Comparative Examples 3 to 6 Silicon nitride powder used in Example 1, MgO.Al ₂ O
₃ Spinel structure powder, silicon carbide powder, silicon oxide powder, aluminum oxide powder and oxides or carbides of Ti, Hf, W are compounded to have a composition ratio shown in Table 2 to form a raw material mixture. Each was prepared. Next, each of the obtained raw material mixtures was molded, degreased, under the same conditions as in Example 1.
Sintering was carried out 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, those in which silicon carbide was excessively added (Comparative Example 3), M
One in which gO.Al ₂ O ₃ spinel structure was excessively added (Comparative Example 4), one in which silicon oxide was excessively added (Comparative Example 5), and one in which titanium oxide was excessively added (Comparative Example 6) were used. Each was prepared and the sintering operation was performed from the raw material mixing under the same conditions as in Example 1, and the corresponding Comparative Examples 3 to 6 were performed.
A silicon nitride sintered body according to the above was produced.

[0032]

[Table 2]

With respect to each of the silicon nitride sintered bodies of Examples 2 to 15 and Comparative Examples 3 to 6 thus obtained, the density, the bending strength and the hardness were respectively measured under the same conditions as in Example 1, and the dipping treatment was carried out. Then, the weight loss and bending strength of each sample were measured. Table 3 shows the measurement results.

[0034]

[Table 3]

As is clear from the results shown in Table 3, the spinel structure, silicon carbide, aluminum oxide, silicon oxide as required, and oxides or carbides of Ti, Hf, and W in predetermined amounts. It was confirmed that each of the added sintered bodies of Examples 2 to 15 exhibited high mechanical properties, reduced weight loss and reduced bending strength after the HCl immersion test, and had excellent chemical resistance. It was

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, the silicon nitride sintered body prepared according to the manufacturing method of Example 12 was processed to manufacture a ceramic ball bearing (ball bearing) as shown in FIG. This ball bearing is configured by interposing a spherical rolling element (silicon nitride ball) 3 between a cylindrical inner ring 1 and an outer ring 2 made of the above 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 carried out in a grease lubrication environment in which hydrochloric acid mist was mixed together with the above ceramic ball bearing. As a result, the ceramic ball bearings, which have superior heat resistance and corrosion resistance, can maintain hardness even at high temperatures compared to conventional steel ball bearings and do not cause seizure, resulting in a life of 10 times or more. It was revealed that the film could be stretched, and it was confirmed that the excellent effect could be exhibited.

[0038]

As described above, according to the silicon nitride sintered body of the present invention, since the grain boundary phase having chemical resistance is formed in the sintered body structure by the spinel structure, corrosion resistance is improved. The mechanical properties can be improved without impairing the original wear resistance and the like of the silicon nitride sintered body. Therefore, it is useful as a silicon nitride sintered body that is extremely useful as a high-strength, wear-resistant, chemical-resistant member, etc., which replaces the conventional corrosion-resistant / heat-resistant alloys, corrosion-resistant cemented carbides, etc. that were used to configure bearing parts and gas turbine parts Is.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a ball bearing (ball bearing) formed of a silicon nitride sintered body according to the present invention.

[Explanation of symbols]

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

Claims (6)

[Claims] 1. Magnesium as a constituent element is 0.1
.About.1.5% by weight, aluminum in the range of 0.1 to 3% by weight, carbon in the range of 0.01 to 6% by weight, oxygen in the range of 0.2 to 5% by weight, the balance being substantially silicon nitride. A silicon nitride sintered body characterized by: 2. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body further comprises at least one selected from titanium, hafnium and tungsten as a constituent element thereof in a range of 0.1 to 3.8. A silicon nitride sintered body, characterized in that the content is in the range of% by weight. 3. An MgO.Al ₂ O ₃ spinel structure of 0.5 to 6% by weight, silicon carbide of 0.1 to 20% by weight,
A silicon nitride sintered body, which is obtained by firing a ceramics mixture containing silicon oxide in an amount of 1% by weight or less, aluminum oxide in an amount of 3% by weight or less, and the balance substantially consisting of silicon nitride. 4. The silicon nitride sintered body according to claim 3, wherein the ceramic mixture further comprises titanium,
A silicon nitride sintered body comprising at least one compound selected from oxides and carbides of hafnium and tungsten in a range of 0.1 to 4% by weight. 5. A chemical resistant member comprising the silicon nitride sintered body according to any one of claims 1 to 4. 6. A bearing member comprising the silicon nitride sintered body according to any one of claims 1 to 4.