JPH06219837A - Silicon nitride ceramic sintered compact and its production - Google Patents

Abstract

PURPOSE:To produce a silicon nitride ceramic sintered compact easily densified with small amts. of auxiliaries, excellent in toughness, strength, wear resistance and rolling fatigue characteristics and suitable for use as a sliding member and a bearing material. CONSTITUTION:A ceramic mixture of 100 pts.wt. silicon nitride with 2-7 pts.wt. yttrium oxide, 0.3-9 pts.wt. aluminum oxide, 0.6-7 pts.wt. MgO.Al2O3 spinel and <=2 pts.wt. at least one among titanium oxide, zirconium oxide, hafnium oxide, molybdenum carbide and tungsten carbide is sintered to obtain the objective silicon nitride ceramic sintered compact.

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 a method for producing the same, and particularly to densification easily with a small amount of additive aid, excellent toughness, wear resistance and rolling fatigue characteristics, and sliding. The present invention relates to a silicon nitride ceramics sintered body suitable as a member and a bearing material and a method for manufacturing the same.

[0002]

2. Description of the Related Art Ceramic sinters containing silicon nitride as a main component are lightweight and have high strength, as well as excellent wear resistance and slidability. It has begun to spread widely as a member and bearing member, and is also used for automobile parts and chemical mechanical parts. In particular, a silicon nitride sintered body has excellent heat resistance in a high temperature range up to about 1900 ° C. and has a small coefficient of thermal expansion.
In addition, since it has better resistance to thermal shock than conventional metal materials, its application is being developed as various high-strength heat-resistant parts materials such as gas turbine blades, gas turbine nozzles, and internal combustion engine parts.

By the way, since silicon nitride is a strong covalently-bonded ceramic, and the sinterability is extremely poor only with the silicon nitride powder forming the sintered body, when a silicon nitride sintered body is usually manufactured, For silicon nitride powder of a predetermined particle size,
A rare earth oxide such as yttrium oxide (Y ₂ O ₃ ) or a metal oxide such as magnesia, alumina or zirconia is added as a sintering aid, and the obtained raw material mixture is formed into a compact by a press molding method. It is manufactured by compacting a compact by pressureless sintering in a vacuum or non-oxidizing atmosphere.

Additives such as the above-mentioned sintering aids exist as a second phase at the grain boundaries after sintering, and the existence form of this second phase greatly affects the characteristics of the silicon nitride ceramics sintered body. That is, when the second phase is amorphous with a low melting point, the high temperature strength of the sintered body is significantly deteriorated. On the other hand, when the second phase is crystalline, the decrease in high temperature strength is small.
Further, it has been found that the absolute amount of the second phase also has a great influence on the wear resistance of the sintered body and especially on the rolling fatigue life when applied to bearing parts. It has been generally confirmed that the characteristics of the sintered body are improved as the absolute amount of the second phase is reduced.

[0005]

However, if the absolute amount of the second phase of the grain boundary is extremely reduced, the mechanical strength and toughness inherent in silicon nitride are impaired, so that the original quality characteristics can be guaranteed. It will be difficult.

On the other hand, conventionally, an organic solvent such as trichloroethane, trichloroethylene or ethyl alcohol has been used in order to uniformly mix the silicon nitride raw material powder and the above-mentioned addition aid. However, while chlorine-based organic solvents such as trichloroethane are highly toxic and their use is being restricted, when flammable solvents such as ethyl alcohol are used, a means to enhance the safety of production equipment is required. However, there were difficulties in manufacturing technology. Therefore, a method of using water as a solvent is also adopted, but there is a problem that an auxiliary agent that reacts with water, such as aluminum nitride (AlN), cannot be used.

As described above, as additive aids used in the production of silicon nitride ceramics sintered bodies, yttrium oxide-aluminum oxide-based materials, zirconium and titanium oxides, molybdenum and tungsten carbides, and the like have been used. The added system is adopted. However, it is required to obtain a sintered body that is dense and has high wear resistance, rolling fatigue strength, mechanical strength and toughness while further increasing the sinterability while reducing the amount of the auxiliary agent that causes a decrease in high temperature strength. Has been done.

The present invention has been made in order to meet the above-mentioned demands and problems, and in particular, it is easily densified with a small amount of an additive aid, and has excellent toughness, wear resistance and rolling fatigue characteristics. An object of the present invention is to provide a silicon nitride ceramics sintered body suitable as a sliding member and a bearing material, and a method for manufacturing the same.

[0009]

In order to achieve the above object, the inventor of the present application prepared a large number of sintered body samples by changing the addition amount of various sintering aids and dispersion strengthening agents, and sintering them. The effects on the sinterability and strength characteristics of the body were quantitatively understood. As a result, MgO.Al ₂ O _{3 is} used as a sintering aid.
By adding spinel (MgAl ₂ O ₄ ) to the yttrium oxide-aluminum oxide-based material, the sintering characteristics are significantly improved, and even when a small amount of an auxiliary agent is added, densification easily proceeds during sintering, A silicon nitride ceramics sintered body excellent in wear resistance, high temperature strength and rolling fatigue resistance was obtained. The present invention has been completed based on these findings.

That is, in the silicon nitride ceramics sintered body according to the present invention, 2 to 7 parts by weight of yttrium oxide and 0.3 to 9 parts of aluminum oxide are used with respect to 100 parts by weight of silicon nitride.
Parts by weight, 0.6 to 7 parts by weight of MgO.Al ₂ O ₃ spinel, and 2 parts by weight or less of at least one selected from titanium oxide, zirconium oxide, hafnium oxide, molybdenum carbide and tungsten carbide. It is characterized in that the mixture is sintered.

The total content of yttrium oxide, aluminum oxide, MgO.Al ₂ O ₃ spinel, titanium oxide, zirconium oxide, hafnium oxide, molybdenum carbide and tungsten carbide is 13 parts by weight or less based on 100 parts by weight of silicon nitride. Good to set.

A method of manufacturing a silicon nitride ceramics sintered body according to the present invention comprises molding the above ceramic mixture,
The obtained molded body is degreased and then sintered or hot isostatic pressing (HIP) is performed at a temperature of 1650 to 1825 ° C. in a non-oxidizing atmosphere.

Here, as the silicon nitride powder, it is preferable to use a fine and highly pure raw material powder having a particle size of 5 μm or less, preferably 2 μm or less. In particular, a raw material powder containing 0.5% by weight or less of impurities such as lithium, potassium, sodium, calcium and iron that form a low melting point compound at the grain boundaries of the sintered body is used. Silicon nitride (Si ₃ N ₄ ) is α
Both of the phase type and the β phase type can be used, but the α phase type silicon nitride has crystal grains grown longer after high temperature sintering and has a higher mechanical strength than the β phase type. Therefore, it is desirable that α-phase type silicon nitride accounts for 80% by weight or more of the entire raw material silicon nitride. Further, in order to secure the thermal shock resistance and wear resistance peculiar to silicon nitride, it is desirable to set the amount of other additive components so that the silicon nitride component ratio in the sintered body is 85% by weight or more.

Yttrium oxide (Y ₂ O ₃ ), which is one of the additional components of the sintered body according to the present invention, reduces the densification rate in the sintering process, but the phase from the α phase type to the β phase type is reduced. It is added in an amount of 2 to 7 parts by weight in order to accelerate the transition rate and accelerate the formation of β-phase type columnar crystals to improve the strength and toughness of the sintered body. If the addition amount is less than 2 parts by weight, the above effect becomes insufficient, while if the addition amount exceeds 7 parts by weight, the mechanical strength and thermal shock resistance of the obtained sintered body are likely to decrease, which is not preferable. .

Aluminum oxide (Al ₂ O ₃ ) is added in an amount of 0.3 to 9 parts by weight in order to increase the high temperature strength and contribute to the promotion of sintering. The effect is great when you do. Addition amount is 0.
If the amount is less than 3 parts by weight, the effect of promoting sintering will be insufficient, while if the amount added exceeds 9 parts by weight, the thermal shock resistance will decrease and the room temperature strength will also tend to deteriorate.

Further, MgO.Al ₂ O ₃ spinel functions as a sintering accelerator in the manufacturing process and can improve the chemical resistance of the sintered body, and is added in an amount of 0.6 to 7 parts by weight. When the addition amount is less than 0.6 parts by weight, the formation of the grain boundary phase becomes insufficient and the chemical resistance of the sintered body at a high temperature tends to decrease, while when the content exceeds 7 parts by weight. In addition, since a large amount of liquid phase having a low melting point is generated after sintering and mechanical strength starts to decrease, the addition amount is set within the above range.

Incidentally, the MgO component and the Al ₂ O ₃ component are not separate, but MgO.Al ₂ O having a high melting point as an auxiliary agent.
By adding in the form of ₃ spinels, the sinterability is greatly improved as compared with the conventional manufacturing method, and in particular, as compared with the case where the conventional sintering aid such as Y ₂ O ₃ or MgO is used, In addition to being able to reduce the addition amount of, the density of the sintered body can be significantly improved. Further, when a sintered body having the same density as that of the sintered body manufactured by the conventional manufacturing method is manufactured, the sintering temperature can be lowered by about 50 to 100 ° C., the manufacturing conditions can be relaxed, and the manufacturing cost can be reduced. Can be planned.

Further, in the manufacturing process of the sintered body according to the present invention, Ti, Zr, which is another component added to the raw material powder,
The oxides of Hf and the carbides of Mo and W are MgO.Al ₂
It acts synergistically with O ₃ spinel to function as a sintering accelerator that promotes densification sintering, and has a grain size of 1 after sintering.
The compound has a high melting point of ˜5 μm and is dispersed as a particle in the grain boundary of the sintered body, and has the effect of improving the strength and wear resistance of the sintered body. On the other hand, it is added at a ratio of 2 parts by weight or less. If the amount added exceeds 2 parts by weight, the chemical resistance and toughness will decrease, while if the amount added is less than 0.1 part by weight, the effect of improving the strength characteristics and wear resistance will not be sufficiently obtained. Therefore, it is preferably added in the range of 0.3 to 1.5 parts by weight.

The above yttrium oxide, aluminum oxide, MgO.Al ₂ O ₃ in the ceramic mixture is used.
Spinel, oxides of Ti, Zr, Hf, and Mo, T
The total addition amount of the sintering aid such as carbide of i is 13 parts by weight or less,
More preferably, it is set in the range of 7 to 10 parts by weight. When the ratio of yttrium oxide to the total amount of aluminum oxide and MgO.Al ₂ O ₃ spinel is less than 0.5, the strength and toughness of the sintered body are significantly decreased, while the ratio value is If it exceeds 3, the densification rate will decrease, so the ratio of each auxiliary component is set so that the value of the above ratio falls within the range of 0.5 to 3.

As described above, the MgO.Al ₂ O ₃ spinel has the effect of increasing the densification rate, but it tends to form a liquid phase having a low melting point after sintering. Therefore, MgO ・ Al ₂
The ratio of aluminum oxide to O ₃ spinel is 0.5-
A range of 5 is desirable. This is because when the ratio value is less than 0.5, the high temperature strength due to the liquid phase is significantly reduced, while when the ratio value exceeds 5, the effect of MgO.Al ₂ O ₃ spinel is relatively reduced. Because it will be.

The silicon nitride ceramics sintered body according to the present invention is manufactured through the following processes, for example. That is, Y ₂ O ₃ as an auxiliary agent for silicon nitride powder,
Al ₂ O ₃ , MgO.Al ₂ O ₃ spinel, Ti,
A predetermined amount of Zr, Hf oxide and at least one powder of Mo, W carbide is added to prepare a ceramic mixture, and the obtained ceramic mixture is then used in a general-purpose die press or the like. After forming a molded body having a predetermined shape by a molding method, the molded body is degreased, and further 1650 to 1825 in a non-oxidizing atmosphere such as nitrogen gas or argon gas.
Baking is performed at a temperature of about C for 1 to 10 hours.

The reason why the firing atmosphere is a non-oxidizing atmosphere such as nitrogen or argon is that in an oxidizing atmosphere containing oxygen or the like, silicon nitride is oxidized during high temperature sintering to change to SiO ₂ and the desired nitriding is performed. This is because the original mechanical strength of the silicon sintered body cannot be obtained.

The above-mentioned firing operation may be carried out by the atmospheric pressure sintering method or another sintering method, for example, a hot pressing method,
You may implement by using an atmosphere pressurizing method, a hot isostatic pressing (HIP) method, etc. In any firing method, it is possible to obtain 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. In particular, since the sinterability is good even by the atmospheric pressure sintering method, the mass productivity of the silicon nitride ceramics sintered body can be greatly improved.

[0024]

According to the silicon nitride ceramics sintered body and the method of manufacturing the same having the above-described structure, a yttrium oxide-aluminum oxide based sintering aid is further used, and MgO.Al ₂ O _{3 is} further added.
Since a predetermined amount of spinel is added, the sintering characteristics are significantly improved even when a small amount of sintering additive is added, while Ti, Zr, Hf oxides and Mo, W carbides are Dispersion in the grain boundaries improves wear resistance and rolling fatigue properties. Therefore, a silicon nitride ceramics sintered body suitable for the sliding member and the bearing member can be obtained.

[0025]

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

Examples 1 to 5 Average particle size of 0.6 μm containing 95% by weight of α-phase type silicon nitride
As shown in the left column of Table 1, Y ₂ O ₃ , Al ₂ O ₃ , MgO.Al ₂ O ₃ spinel, MoC, etc. were used as a sintering aid and a dispersion strengthener for 100 parts by weight of the silicon nitride powder of m. 5 kinds of ceramics mixtures were prepared by adding a predetermined amount each. Next, each ceramic mixture obtained is wet-mixed with ethanol as a solvent in an alumina pot for 48 hours, then dried, and pressure-molded with a press molding machine at a molding pressure of 800 kgf / cm ² , to obtain a length of 50 mm x a width of 50 mm x A large number of 10 mm thick molded bodies 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 heated at a temperature of 18 at a pressure of 5 atm in a nitrogen gas atmosphere.
After pressure calcination at 00 ° C, hot isostatic pressure (HIP) treatment was further performed at a temperature of 1700 ° C and a pressure of 1000 atm.
Silicon nitride ceramics sintered bodies according to Examples 1 to 5 were prepared.

Comparative Examples 1 to 6 On the other hand, as Comparative Examples 1 to 6, the addition amounts of Y ₂ O ₃ , Al ₂ O ₃ , MgO.Al ₂ O ₃ spinel, MoC and the like as sintering aids and dispersion strengtheners. Was treated in the same manner as in Examples 1 to 5 except that the amount was set to be too small or too large as shown in the left column of Table 1, to prepare silicon nitride ceramics sintered bodies according to Comparative Examples 1 to 6, respectively.

Three-point bending strength, Vickers hardness (Hv), and fracture toughness values at normal temperature and 1000 ° C. of the silicon nitride ceramics sintered bodies (samples) according to Examples 1 to 5 and Comparative Examples 1 to 6 thus prepared And the specific wear amount was measured.

The bending strength values were measured by a 3-point bending strength tester, and the sample size was 4 mm × 3 mm × 4.
0mm, crosshead speed 0.5mm / min, span 30
It was measured under the test condition of mm. The measurement operation of each sample was performed 5 times, and the average value is shown. The fracture toughness value was measured using the microindentation method.

Further, the specific wear amount was measured using a block-on-ring type FALEX wear tester as shown in FIG. The wear tester 1 shown in FIG. 1 has a steel ring 3 with a lower end portion immersed in an engine oil 2 and a Si ₃ N ₄ sample block 4 pressed against the upper outer peripheral surface of the steel ring 3 with a predetermined load P. The specific wear amount of the Si ₃ N ₄ sample block 4 was measured by continuously rotating in a predetermined rotation direction for 6 hours. The load P as sample conditions was set to 150 kgf, the peripheral speed of the steel ring 3 was set to 1.2 m / sec, and the temperature of the engine oil 2 was set to 125 ° C.

The measurement results are shown in Table 1 below.

[0033]

[Table 1]

As is clear from the results shown in Table 1, according to the Si ₃ N ₄ sintered bodies according to Examples 1 to 5, bending strength,
The hardness, fracture toughness value, and specific wear amount were relatively higher than those of Comparative Examples 1 to 6, and a high-quality sintered body having excellent mechanical strength was obtained.

[0035]

As described above, according to the silicon nitride ceramics sintered body and the method for manufacturing the same according to the present invention, a yttrium oxide-aluminum oxide based sintering aid is further provided with MgO.Al ₂ O ₃ spinel. Since a fixed amount is added, the sintering characteristics are significantly improved even when a small amount of sintering additive is added, while oxides of Ti, Zr, Hf,
Further, carbides of Mo and W are dispersed in the grain boundaries, and wear resistance and rolling fatigue characteristics are improved. Therefore, a silicon nitride ceramics sintered body suitable for the sliding member and the bearing member can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of a Falex wear tester.

[Explanation of symbols]

1 abrasion tester 2 engine oil 3 steel ring 4 Si ₃ N ₄ sample block P load

Claims (2)

[Claims] 1. Yttrium oxide in an amount of 2 to 7 parts by weight and aluminum oxide in an amount of 0.3 to 100 parts by weight of silicon nitride.
9 parts by weight and 0.6 to 7 of MgO.Al ₂ O ₃ spinel
A silicon nitride ceramic calcination, characterized by comprising, by weight, a ceramic mixture containing 2 parts by weight or less of at least one selected from titanium oxide, zirconium oxide, hafnium oxide, molybdenum carbide and tungsten carbide. Union. 2. Yttrium oxide in an amount of 2 to 7 parts by weight and aluminum oxide in an amount of 0.3 to 100 parts by weight of silicon nitride.
9 parts by weight and 0.6 to 7 of MgO.Al ₂ O ₃ spinel
Parts by weight and at least one selected from titanium oxide, zirconium oxide, hafnium oxide, molybdenum carbide, and tungsten carbide in an amount of 2 parts by weight or less are molded into a ceramic mixture, and after degreasing the resulting molded body, A method for producing a silicon nitride ceramics sintered body, which comprises sintering or hot isostatic pressing (HIP) at a temperature of 1650 to 1825 ° C. in an oxidizing atmosphere.