JPH05238829A - Sintered silicone nitride ceramic - Google Patents

Abstract

PURPOSE:To provide a sintered silicon nitride ceramic having improved mechanical strength under high-temperature condition and especially further improved oxidation resistance under severe temperature condition at >=1200 deg.C. CONSTITUTION:The objective sintered silicon nitride ceramic is produced by baking a ceramic mixture composed of 1-10wt.% of MgO.Al2O3 spinel structure, 1-10wt.% of aluminum nitride, 0.1-5wt.% of at least one kind of compound selected from oxide, carbide or silicide of Hf, Nb or Ti and the remaining part of silicon nitride.

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, and particularly to a silicon nitride ceramics sintered body having not only excellent mechanical strength at high temperature use but also excellent oxidation 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.

Conventionally, 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, magnesium or zirconium oxides and the like are known.

Oxides of rare earth elements such as yttrium oxide (Y ₂ O ₃ ) in the above-mentioned sintering composition have been generally used as a sintering aid from the past, and enhance the sinterability to densify the sintered body. , Is added to prevent the strength deterioration of the sintered body at high temperature. Then, by adding a combination of a plurality of kinds of oxides, it is devised so as to exhibit excellent mechanical strength even in a severe use environment at high temperature.

[0005]

However, any of the ceramic sintered bodies having the above composition still has insufficient oxidation resistance in a high temperature environment, particularly in a use environment of reaching 1200 ° C. or higher, and thus the structure for high temperature use is high. When it is used as a material, the predetermined durability and reliability cannot be obtained, and improvement in oxidation resistance is strongly desired.

In particular, in recent years, in a combustion engine such as a gas turbine, in order to improve the operation efficiency, the practical use has been promoted in the direction of significantly increasing the operation temperature and the pressure as compared with the conventional case. Therefore, there is a demand for the development of a silicon nitride ceramics sintered body that has little deterioration in mechanical properties even in high-temperature combustion exhaust gas containing a large amount of oxidizing components.

The present invention has been made in order to meet the above-mentioned demands, and improves the mechanical strength under high temperature conditions and, particularly, the oxidation resistance under severe temperature conditions of 1200 ° C. or higher. It is an object of the present invention to provide a silicon nitride ceramics sintered body having further improved properties.

[0008]

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, some spinel structures and H
When a predetermined amount of each of f, Nb or Ti oxide and aluminum nitride is added to the silicon nitride raw material, it has great oxidation resistance even under high temperature conditions exceeding 1300 ° C. It was found that a silicon nitride ceramics sintered body with little 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 MgO.Al ₂ O ₃ spinel structure 1 to
10% by weight and 1 to 10% by weight of aluminum nitride,
Firing a ceramic mixture consisting of 0.1 to 5% by weight of at least one selected from the group consisting of oxides, carbides or suicides of Hf, Nb or Ti, and silicon nitride constituting the balance. It is characterized by

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 plays a role in forming a protective film having a large oxidation resistance on the surface of the sintered body, so In the range of 1 to 10% by weight. If the amount added is less than 1% by weight, the formation of the above-mentioned protective film will be insufficient, and the deterioration of mechanical strength of the obtained sintered body at high temperature, particularly in an oxidizing atmosphere of 1200 ° C or higher, can be prevented. The function to do is not fully exerted. On the other hand, the addition amount is 10% by weight
If the amount exceeds the limit, the high temperature strength will start to decrease, and therefore the above range is set. Especially preferably 2-5
It is desirable to set the weight.

Incidentally, instead of the above spinel structure, Mg
When the mixture of O powder and Al ₂ O ₃ powder is added, α-sialon (Si-Al-O-N) is easily formed, and the original properties of the silicon nitride based sintered body are obtained. It is not preferable because it cannot be done.

Further, by adding the above 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 manufacturing method, and the density improving effect of the sintered body becomes remarkable. .. Further, when a sintered body having the same density as that of the conventional manufacturing method is produced, the sintering temperature is set to 50 to 10
It is possible to lower the temperature by about 0 ° C., the manufacturing conditions can be relaxed, and the manufacturing cost can be reduced.

Further, aluminum nitride (AlN) as another component added to the raw material powder in the present invention not only increases the mechanical strength of the sintered body in a high temperature range but also contributes to the promotion of sintering. In particular, it exhibits a remarkable effect when performing normal pressure sintering. When the addition amount is less than 1% by weight, the improvement of the high temperature strength and the sinterability are insufficient, while when the addition amount exceeds 10% by weight, the strength of the sintered body at normal temperature deteriorates. Therefore, the addition amount is set in the range of 1 to 10% 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 3 to 6% by weight.

In addition, the oxides, carbides or silicides of Hf, Nb or Ti, which are other components added to the raw material powder in the manufacturing process of the sintered body according to the present invention, function as a sintering promoter and It becomes a high-melting point compound after binding and has a form in which it is dispersed as particles in the sintered body structure independently, and has the effect of improving the wear resistance of the sintered body. It is added in the range of% by weight.

If the amount added is less than 0.1% by weight, the effect of improving high-temperature strength and wear resistance is small, while if the amount added exceeds 5% by weight, the high-temperature strength decreases.
In order to maintain the mechanical strength of the sintered body at an optimum value, it is desirable to set the content in the range of preferably 0.3 to 5% by weight, more preferably 1 to 4% by weight.

As the silicon nitride (Si ₃ N ₄ ) which is the main component of the sintered body according to the present invention, both of rhombohedral α-phase type and 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. Furthermore, 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 8
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 through the following processes, for example.
That is, with respect to silicon nitride powder, MgO.Al ₂ O ₃ spinel structure powder, aluminum nitride powder, Hf,
A predetermined amount of at least one powder selected from the group consisting of oxides, carbides, and silicides of Nb or Ti is added to prepare a raw material mixture, and the obtained raw material mixture is then die-pressed. After being formed into a molded product having a predetermined shape by a general-purpose molding method such as the above, the molded product is fired at a temperature of about 1700 to 1800 ° C. for a predetermined time in an atmosphere of an inert gas such as nitrogen gas or argon.

The reason why the firing atmosphere is an inert gas atmosphere such as nitrogen or argon is that the silicon nitride is oxidized during high temperature sintering in an oxidizing atmosphere containing oxygen or the like and SiO _{2 is used.}
This is because the desired high-temperature 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 such as a hot pressing method,
It may be carried out by using an atmospheric pressure method, a hot isostatic pressing method (HIP) or the like. Dense in any firing method,
In addition, a silicon nitride ceramics sintered body having high temperature mechanical strength, particularly excellent oxidation resistance in a high temperature environment exceeding 1200 ° C., 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.

[0021]

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

Example 1 and Comparative Example 1 Average particle size of 0.6 μm containing 95 wt% of α-phase silicon nitride
88% by weight of silicon nitride powder, 5% by weight of MgO.Al ₂ O ₃ spinel structure powder having an average particle size of 0.8 μm, and 5% by weight of aluminum nitride powder having an average particle size of 0.9 μm,
A mixture with 2% by weight of hafnium oxide powder having an average particle diameter of 0.8 μm was mixed with ethanol as a solvent in a ball mill for 24 hours.
The materials were mixed for a time to prepare a uniform raw material powder mixture.

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, after degreasing the obtained molded body in a nitrogen gas atmosphere at a temperature of 500 ° C. for 2 hours, the degreased body was subjected to normal pressure sintering at a temperature of 1775 ° C. for 2 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,
5% by weight of yttrium oxide (Y ₂ O ₃ ) having an average particle size of 0.9 μm is used instead of the MgO · Al ₂ O ₃ spinel structure.
Mixing of raw materials, molding under the same conditions as in Example 1 except that the addition was performed,
The silicon nitride ceramics sintered body according to Comparative Example 1 was prepared by degreasing and sintering.

With respect to the silicon nitride ceramics sintered bodies (samples) according to Example 1 and Comparative Example 1 thus obtained, the bending strength at room temperature (room temperature of 25 ° C.) and 1300 ° C. was measured. In order to evaluate the properties, each sample was heated in air at 1300 ° C. for 5 hours to carry out an oxidation treatment, and the bending strength of each sample after the oxidation treatment at room temperature was measured to obtain the results shown in Table 1 below. It was

[0027]

[Table 1]

The bending strength values in Table 1 are measured by a three-point bending strength test, and the sample size is 4 mm ×
3mm x 40mm, crosshead speed 0.5mm / min,
The measurement was performed under the test conditions of a span of 30 mm. The measurement operation at each temperature was carried out four times, and the average value is shown.

As is clear from the results shown in Table 1, the sintered body according to Example 1 exhibits a high bending strength value even after the oxidation treatment, and is excellent in oxidation resistance at high temperatures. On the other hand, in the sintered body of Comparative Example 1 in which the conventional sintering aid (Y ₂ O ₃ ) was added without adding the spinel structure, it was almost the same as the sintered body of Example 1 before the oxidation treatment. Although it has characteristics, it was found that the strength was significantly reduced after the high temperature oxidation treatment.

Examples 2 to 12 and Comparative Examples 2 to 9 As Examples 2 to 12, the silicon nitride powder used in Example 1, the MgO.Al ₂ O ₃ spinel structure powder, and the aluminum nitride powder, Hafnium oxide powder,
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 respective raw material mixtures.

Next, the respective raw material mixtures thus obtained were mixed under the same conditions as in Example 1, raw materials were mixed, molded, degreased and sintered to produce silicon nitride sintered bodies according to Examples 2 to 12, respectively.

On the other hand, as shown in the left column of Table 2 as Comparative Examples 2 to 9, a metal compound added in an excessive amount (Comparative Example 2),
An excessive amount of AlN powder (Comparative Example 3), an excessive amount of spinel structure (Comparative Example 4), no spinel structure (Comparative Example 5), a spinel structure and AlN powder were used. No addition (Comparative Example 6), no metal compound (Comparative Example 7), Al
A raw material mixture was prepared in which neither the N powder nor the metal compound was added (Comparative Example 8) and the AlN powder was not added (Comparative Example 9), and the sintering operation was performed from the raw material mixing under the same conditions as in Example 1. It carried out and manufactured the sintered compact which concerns on Comparative Examples 2-9, respectively.

The yttrium oxide powder used in Comparative Examples 5 and 6 was the same as that used in Comparative Example 1, and the Al ₂ O ₃ powder used had an average particle size of 0.9 μm.

With respect to the silicon nitride ceramics sintered bodies according to Examples 2 to 12 and Comparative Examples 2 to 9 thus manufactured, the bending strengths before and after the oxidation treatment were measured under the same conditions as in Example 1, and Table 2 below. The results shown in the right column were obtained.

[0035]

[Table 2]

As is clear from the results shown in Table 2, the sintered bodies according to Examples 2 to 12 each containing a predetermined amount of the spinel structure, aluminum nitride and metal compound had high bending even after the oxidation treatment. It has strength values, and it was confirmed that it has excellent oxidation resistance in a high temperature environment.

On the other hand, as shown in Comparative Examples 2 to 9, when at least one component of the above spinel structure, aluminum nitride and metal compound is added in an excessive amount or is insufficient, especially after the oxidation treatment. It was confirmed that the bending strength tended to decrease and the oxidation resistance at high temperature was poor.

[0038]

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, aluminum nitride and H
The compound of f, Nb or Ti is added in combination, and since the oxidation resistant film is formed on the surface of the sintered body by the spinel structure in particular, it has excellent mechanical strength even at high temperature, and more than 1200 ° C. The mechanical strength is not significantly reduced even in the high temperature oxidizing atmosphere. Therefore, it is extremely useful as a high-strength heat-resistant member that replaces conventional heat-resistant superalloys such as gas turbine parts.

Claims (2)

[Claims] 1. A MgO.Al ₂ O ₃ spinel structure is used.
-10 wt% and aluminum nitride 1-10 wt%
And 0.1 to at least one selected from the group consisting of oxides, carbides or silicides of Hf, Nb or Ti.
A silicon nitride ceramics sintered body obtained by firing a ceramics mixture composed of 5% by weight and the remaining silicon nitride. 2. The α-phase type silicon nitride in the silicon nitride raw material powder is 80% by weight or more.
The described silicon nitride ceramics sintered body.