JPH05294730A - Silicon nitride ceramic sintered compact - Google Patents

Abstract

PURPOSE:To obtain a silicon nitride ceramic sintered compact having excellent resistance to chemicals such as acids without deteriorating excellent strength, wear and heat resistance proper to silicon nitride. CONSTITUTION:A ceramic mixture consisting of 0.5-3wt.% MgO.Al2O3 spinel structure, 0.1-2wt.% at least, one of the oxides and carbides of Hf and Ti and the balance silicon nitride is fired. The oxide of at least one among Ca, Li, Sr and Si may be added to the ceramic mixture by 0.1-2wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride ceramics sintered body, which has particularly excellent mechanical strength and wear resistance as well as excellent chemical resistance. Regarding the body

[0002]

2. Description of the Related Art Ceramic sintered bodies containing silicon nitride as a main component have excellent heat resistance even in an environment of 1000 ° C. or higher, and also have excellent thermal shock resistance due to a low coefficient of thermal expansion. Because of its properties, it has been attempted to be applied to various high-strength heat-resistant parts such as gas turbine parts, engine parts, and steel-making machine parts as a high-temperature structural material replacing conventional heat-resistant superalloys. In addition, since it has excellent corrosion resistance to metals, it has been tried to apply molten metal as a melt-resistant material, and because it has excellent wear resistance, it can be put to practical use in sliding members such as bearings and cutting tools. ing.

Since it is difficult to sinter silicon nitride or its raw material powder alone, a rare earth oxide, magnesium oxide or the like as a sintering aid is usually added to the raw material powder in a predetermined amount to improve the sinterability. And made into a high-strength ceramics sintered body.

For example, as a sintering composition of a silicon nitride ceramics sintered body, silicon nitride-yttrium oxide-aluminum oxide system, silicon nitride-yttrium oxide-aluminum oxide-aluminum nitride system, silicon nitride-yttrium oxide-aluminum oxide-titanium. , Oxides of magnesium or zirconium, etc. are known.

A ceramic sintered body formed by adding an oxide of a rare earth element such as yttrium oxide (Y ₂ O ₃ ) or aluminum oxide in the above-mentioned sintering composition has high sinterability and becomes dense. It has excellent mechanical strength characteristics and can prevent strength deterioration of the sintered body at high temperature. In addition, by adding a combination of multiple types of oxides such as nitrides such as aluminum nitride and titanium oxide, it has high strength, excellent heat resistance and wear resistance, and is excellent even in high temperature and harsh operating environments. It is designed to exert mechanical strength.

[0006]

However, although the ceramic sintered bodies having the above composition have high strength and excellent heat resistance and wear resistance, they are all resistant to chemicals such as acids (chemical resistance). However, when used as a structural material used in an environment in which chemicals are mixed, predetermined durability and reliability cannot be obtained. On the other hand, a sintered body made of β-sialon is widely used as a material having excellent chemical resistance (acid resistance), but it has a drawback that its application range is limited due to insufficient mechanical properties. there were.

In recent years, in particular, in combustion engines such as gas turbines such as aircraft engines, in order to improve the operating efficiency, the practical use has been promoted in the direction of significantly increasing the rotational speed, the operating temperature and the pressure as compared with conventional ones. However, the bearings are also required to respond to the sophistication. In addition, bearings that can be used in environments with large amounts of chemical substances, such as in the field of offshore development, are also required, and it is difficult to use conventional metal rolling bearings, so chemical resistance, heat resistance, corrosion resistance, etc. There is an increasing number of attempts to apply ceramic materials, which have superior characteristics to metals, to rolling bearings.

The present invention has been made in order to meet the above-mentioned demands, and it does not impair the excellent strength, wear resistance and heat resistance originally possessed by silicon nitride, and further chemistry such as acid. An object is to provide a silicon nitride ceramics sintered body having excellent resistance to chemicals.

[0009]

In order to achieve the above-mentioned object, the present inventors have proposed a sintering aid which is generally used when producing a conventional silicon nitride ceramics sintered body,
In addition to the additives, various compounds were added to the raw materials, and the effects of the addition of the compounds on the properties of the sintered body as the final product were confirmed by experiments.

As a result, a certain spinel structure and H
When a predetermined amount of each of oxides of f and Ti and, if necessary, at least one of calcium oxide, lithium oxide, strontium oxide, and silicon oxide is added to a silicon nitride raw material as a sintering aid. It has been found that a silicon nitride ceramics sintered body having particularly excellent chemical resistance (acid resistance) and having little strength deterioration can be obtained.

The present invention has been completed based on the above findings. That is, the silicon nitride ceramics sintered body according to the present invention has a MgO.Al ₂ O ₃ spinel structure of 0.
5 to 3% by weight, 0.1 to 2% by weight of at least one kind of oxides and carbides of Hf and Ti, and silicon nitride constituting the balance, by firing a ceramic mixture. Characterize.

Further, the above spinel structure, Hf and T
In addition to at least one of the oxides and carbides of i, 0.1 to 2% by weight of ceramics is optionally mixed with at least one selected from the group consisting of calcium oxide, lithium oxide, strontium oxide and silicon oxide. It may be contained in the body.

Further, the above M in the ceramic mixture
gO.Al ₂ O ₃ spinel structure, oxides and carbides of Hf and Ti, calcium oxide, lithium oxide, strontium oxide and silicon oxide, etc. It is good to set it in the range.

Mg added to the silicon nitride raw material powder in the process of manufacturing the ceramic sintered body according to the present invention.
The O.Al ₂ O ₃ spinel structure has a cubic crystal structure and has eight chemical units (MgO.Al ₂ O) in the unit cell.
₃ ) is included. This MgO.Al ₂ O ₃ spinel structure not only functions as a sintering accelerator in the manufacturing process, but also forms a grain boundary phase that has a strong resistance to chemicals to improve the chemical resistance of the sintered body. In order to improve, it is added to the raw material powder in the range of 0.5 to 3% by weight. If the addition amount is less than 0.5% by weight, the formation of the grain boundary phase becomes insufficient, and the strength of the sintered body deteriorates when the obtained sintered body is used in an atmosphere in which chemicals are mixed. The preventive function is not fully exerted. On the other hand, if the added amount is too much over 3% by weight, the chemical resistance and mechanical strength will start to decrease, and therefore the above range is set. It is particularly desirable to set the weight to 1 to 2 weights.

By adding the above-mentioned MgO component and Al ₂ O ₃ component in the form of a spinel structure, the sinterability is greatly improved as compared with the conventional production method, and particularly, Y ₂ O ₃ and MgO are not added. Compared with the case of using a conventional sintering aid, the amount of the additive added can be reduced, and the density of the sintered body can be significantly improved. Further, when a sintered body having the same density as that of the conventional sintered body is produced, the sintering temperature is 50 to 1
It is possible to lower the temperature by about 00 ° C., the manufacturing conditions can be relaxed, and the manufacturing cost can be reduced.

Further, Hf and T which are other components added to the raw material powder in the manufacturing process of the sintered body according to the present invention.
The oxides and carbides of i act synergistically with the MgO.Al ₂ O ₃ spinel structure, function as a sintering accelerator that promotes densification sintering, and become a high melting point compound after sintering. , Has a form of being dispersed as a particle in the sintered body structure independently, has an effect of improving the strength and wear resistance of the sintered body, and is added to the raw material powder in the range of 0.1 to 2% by weight. To be done.

When the added amount is less than 0.1% by weight, the effect of improving the strength characteristics and wear resistance is small, while when the added amount exceeds 2% by weight, the chemical resistance mainly composed of acid resistance is low. Will fall. In order to maintain both the mechanical strength and the chemical resistance of the sintered body in an optimum manner, it is more preferable to set it in the range of 1 to 4% by weight.

Further, calcium oxide, lithium oxide, strontium oxide and silicon oxide as other components added to the raw material powder in the present invention increase the mechanical strength of the sintered body in a high temperature region and at the same time promote the sintering. Also contributes, and particularly, it exerts a remarkable effect when performing atmospheric pressure sintering. The amount added is 0.1% by weight
If the amount is less than the above, the improvement of the high temperature strength and the sinterability are insufficient, while if the amount exceeds 2% by weight, the strength of the sintered body at ordinary temperature deteriorates. Is set in the range of 0.1 to 2% by weight. In particular, in order to secure good strength at both normal temperature and high temperature, it is desirable to set the addition amount in the range of 0.25 to 1% by weight.

The above M in the ceramic mixture is
The total addition amount of the sintering aids such as gO.Al ₂ O ₃ spinel structure, Hf and Ti oxides and carbides, calcium oxide, lithium oxide, strontium oxide and silicon oxide is 1.5 to 5% by weight. Range, more preferably 2
It is preferable to set it in the range of 3.5% by weight. The sintered body whose addition amount is within the above range is particularly excellent in both chemical resistance (acid resistance) and mechanical strength.

As the silicon nitride (Si ₃ N ₄ ) which is the main component of the sintered body according to the present invention, both of the rhombohedral α-phase type and the hexagonal β-phase type are used. However, compared with β-phase type, α-phase type silicon nitride can grow longer after high temperature sintering and can maintain high mechanical strength. It is desirable that α-phase silicon nitride accounts for 80% by weight or more of the whole. Further, in order to secure the thermal shock resistance and wear resistance peculiar to silicon nitride, the silicon nitride component ratio in the sintered body is 9%.
It is desirable to set the amount of other additive components so as to be 5% by weight or more. The silicon nitride ceramics sintered body according to the present invention is manufactured, for example, through the following processes. That is, with respect to the silicon nitride powder, MgO.Al ₂ O
₃ spinel structure powder, at least one powder of oxides and carbides of Hf and Ti, and optionally calcium oxide, lithium oxide, strontium oxide,
A predetermined amount of at least one kind of powder selected from the group consisting of silicon oxide is added to prepare a raw material mixture, and the obtained raw material mixture is then shaped into a predetermined shape by a general-purpose molding method such as a die press. After forming the molded body of 1700, this molded body is treated with 1700 to 1 in an inert gas atmosphere such as nitrogen gas or argon.
Baking is performed at a temperature of about 800 ° C. for a predetermined time.

[0021] Here, the reason for the firing atmosphere with an inert gas atmosphere such as nitrogen or argon, in an oxidizing atmosphere containing oxygen such as is silicon nitride oxide during high temperature sintering SiO ₂
This is because the original mechanical strength of the intended silicon nitride sintered body cannot be obtained.

The above-mentioned firing operation may be carried out by a normal pressure sintering method or another sintering method, for example, a hot pressing method,
It may be carried out by using an atmospheric pressure method, a hot isostatic pressing method (HIP) or the like. In any of the firing methods, a silicon nitride ceramics sintered body which is dense and has high mechanical strength and which has excellent chemical resistance particularly in a use environment in which chemicals such as acids are mixed can be obtained. In particular, since the sinterability is good even by the atmospheric pressure sintering method, it is possible to greatly improve the mass productivity of the silicon nitride ceramics sintered body.

[0023]

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

Example 1 and Comparative Examples 1-2 Average particle size of 0.6 μm containing 95 wt% of α-phase silicon nitride
Silicon nitride powder of 96.5% by weight and average particle size of 0.8μ
of MgO.Al ₂ O ₃ spinel structure powder (2.5% by weight) and hafnium oxide powder (average particle diameter: 0.8 μm) (1% by weight) were mixed for 24 hours in a ball mill using ethanol as a solvent to obtain a uniform mixture. A raw material powder mixture was prepared.

Next, a predetermined amount of an organic binder was added to the obtained raw material powder mixture and the mixture was uniformly mixed.
50mm in length x 50mm in width by pressure molding at a molding pressure of / cm ^2.
× Many molded products having a thickness of 5 mm were manufactured.

Next, the molded body thus obtained was degreased in a nitrogen gas atmosphere at a temperature of 500 ° C. for 2 hours, and then the degreased body was subjected to atmospheric pressure sintering at a temperature of 1775 ° C. for 4 hours in a nitrogen gas atmosphere. A silicon nitride ceramics sintered body according to Example 1 was prepared.

On the other hand, as Comparative Example 1, in Example 1,
2% by weight of yttrium oxide (Y ₂ O ₃ ) having an average particle diameter of 0.9 μm instead of the MgO · Al ₂ O ₃ spinel structure.
And 2% by weight of aluminum oxide powder having an average particle size of 0.9 μm were added to 96% by weight of silicon nitride powder, and raw materials were mixed, molded, degreased, and sintered under the same conditions as in Example 1 to obtain a comparative example. A silicon nitride ceramics sintered body according to No. 1 was prepared.

In Comparative Example 2, the raw material mixing, molding, degreasing and sintering treatments were carried out under the same conditions as in Example 1 except that β-phase type sialon powder (z = 2) was used, and the silicon nitride according to Comparative Example 2 was used. An elemental ceramics sintered body was prepared.

Example 1 and Comparative Examples 1 and 2 thus obtained
After measuring relative density, bending strength and fracture toughness at room temperature (room temperature of 25 ° C.), the silicon nitride ceramics sintered body (sample) according to
In order to evaluate the
Solution, HNO ₃ solution, H ₂ SO ₄ solution
Immersion treatment was performed by heating at 100 ° C. for 100 hours, and the weight reduction of each sample after the immersion treatment was measured, and the results shown in Table 1 below were obtained.

[0030]

[Table 1] The bending strength values in Table 1 were measured by a 3-point bending strength test, and the sample size was 4 mm x 3 mm x 40 m.
m, crosshead speed 0.5 mm / min, span 30 m
It was measured under a test condition of m. The measurement operation of each sample was carried out four times, and the average value is shown. The fracture toughness value was measured using the microindentation method.

As is clear from the results shown in Table 1, the sintered body according to Example 1 has a relatively high density, bending strength, fracture toughness value, excellent mechanical strength, and weight reduction after immersion treatment. It has little chemical resistance. On the other hand, in the sintered body of Comparative Example 1 in which the conventional sintering aids (Y ₂ O ₃ and Al ₂ O ₃ ) were added without adding the spinel structure, the weight reduction after the immersion treatment was large, It was found that the chemical resistance was reduced and the mechanical strength was also significantly reduced. It was also found that the sintered body of Comparative Example 2 using β-phase type sialon as the ceramic raw material powder has a good chemical resistance, but the bending strength and the fracture toughness value are significantly reduced.

Examples 2 to 13 and Comparative Examples 3 to 5 As Examples 2 to 13, the silicon nitride powder used in Example 1, the MgO.Al ₂ O ₃ spinel structure powder and hafnium (Hf) were used. Oxide or carbide powder,
Table 2 shows oxides or carbides of Ti having an average particle size of 0.8μ.
Various metal compound powders shown in Table 2 were blended so as to have the composition ratio shown in the left column of Table 2 to prepare raw material mixtures.

Next, the raw material mixture thus obtained was mixed, molded, degreased and sintered under the same conditions as in Example 1 to produce silicon nitride sintered bodies according to Examples 2 to 13, respectively.

On the other hand, as shown in the left column of Table 2 as Comparative Examples 3 to 5, those containing hafnium oxide in excess (Comparative Example 3), those containing spinel structure in excess (Comparative Example 4), and hafnium. A raw material mixture containing no compound (Comparative Example 5) was prepared, and the sintering operation was performed from the raw material mixing under the same conditions as in Example 1, and Comparative Example 3 was performed.
The sintered bodies according to ~ 5 were manufactured.

With respect to the silicon nitride ceramics sintered bodies according to Examples 2 to 13 and Comparative Examples 3 to 5 thus manufactured, the relative density and bending strength were measured under the same conditions as in Example 1, and the dipping treatment was performed. The weight loss of each sample was measured and the results shown in the right column of Table 2 below were obtained.

[0036]

[Table 2]

As is clear from the results shown in Table 2, the sintered bodies according to Examples 2 to 13 containing the spinel structure, the oxides or carbides of hafnium and Ti and, if necessary, the metal compounds in the predetermined amounts, respectively. It was confirmed that all of them had high bending strength values and excellent chemical resistance.

On the other hand, as shown in Comparative Examples 3 to 5, when at least one component of the above spinel structure, hafnium compound and metal compound is added in an excessive amount or insufficient, the bending strength decreases. It was also confirmed that the chemical resistance was poor.

Further, using the silicon nitride ceramics sintered body prepared by the manufacturing method according to Example 1 as a chemical resistant member,
The ball bearing shown in FIG. 1 was prototyped. This ball bearing has an inner diameter of 80 mm
A plurality of ball-shaped rolling elements 3 are provided in the annular gap of a pair of concentric race rings composed of the inner ring 1 and the outer ring 2. The rolling elements 3 are held by the cage 4 at predetermined intervals. Then, at least one part of the inner ring 1, the outer ring 2 and the rolling element 3 is formed of the silicon nitride ceramics sintered body according to the first embodiment, and the ball bearings of each combination are rotated under a grease lubrication condition in which hydrochloric acid mist is mixed. The operating time (life) until peeling, abrasion or cracking of the ceramic sintered body portion was measured at a high speed of several 10,000 rpm as compared with a conventional steel ball bearing, and 1.3 to 2. 1
The life could be extended twice as long.

[0040]

As described above, according to the silicon nitride ceramics sintered body of the present invention, MgO.A is contained in the raw material powder.
l ₂ O ₃ spinel structure, compound of Hf and Ti, and oxides of Ca, Li, Sr, Si if necessary added in combination, and in particular, particles having chemical properties in the sintered body structure due to the spinel structure Since the boundary phase is formed, it has excellent chemical resistance, and further, the mechanical strength is improved without impairing the original wear resistance of the silicon nitride sintered body. Therefore, it is extremely useful as a high-strength, wear-resistant, and chemical-resistant member that replaces the conventional corrosion-resistant superalloys that have been used in bearings, gas turbine parts, and the like.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a ball bearing formed of a silicon nitride ceramics sintered body according to the present invention.

[Explanation of symbols]

 1 inner ring 2 outer ring 3 rolling element 4 cage

Claims (5)

[Claims] 1. The MgO.Al ₂ O ₃ spinel structure comprises 0.5 to 3% by weight, at least one of Hf and Ti oxides and carbides constitutes 0.1 to 2% by weight, and the balance constitutes. A silicon nitride ceramics sintered body obtained by firing a ceramics mixture containing silicon nitride. 2. A MgO.Al ₂ O ₃ spinel structure in an amount of 0.5 to 3% by weight, at least one of Hf and Ti oxides and carbides in an amount of 0.1 to 2% by weight, calcium oxide, 0.1 at least one selected from the group consisting of lithium oxide, strontium oxide and silicon oxide.
A silicon nitride ceramics sintered body obtained by firing a ceramics mixture consisting of ˜2% by weight and the balance silicon nitride. 3. The MgO in the ceramic mixture.
The total addition amount of sintering aids such as Al ₂ O ₃ spinel structure, Hf and Ti oxides and carbides, calcium oxide, lithium oxide, strontium oxide and silicon oxide is in the range of 1.5 to 5% by weight. 3. The silicon nitride ceramics sintered body according to claim 1 or 2, characterized in that 4. The α-phase type silicon nitride in the silicon nitride raw material powder is 80% by weight or more.
Alternatively, the silicon nitride ceramics sintered body according to item 2. 5. A chemical resistant member formed of the silicon nitride ceramics sintered body according to claim 1.