JPH09301771A - Method for producing silicon nitride based sintered body - Google Patents

Abstract

(57) Abstract: To provide a method for manufacturing a silicon nitride sintered body, which is capable of maintaining a healing effect against scratches and defects of the silicon nitride sintered body and increasing internal high temperature strength. . SOLUTION: S having an average particle size of 0.75 μm and an α ratio of 95%
Rare earth oxides having an average particle diameter of 1 to 3 μm, Al compounds, 5a group element oxides, 6a group element oxides and the like are appropriately added to the i ₃ N ₄ powder, wet mixed, and dried with a spray dryer. . After isostatic pressing the obtained powder,
Sintering was carried out by pressureless sintering to obtain a sintered body. The obtained sintered body is first subjected to heat treatment by heating at a relatively low temperature for 8 hours in an oxidizing atmosphere in order to obtain a healing effect, and thereafter, in order to improve the internal high temperature strength, nitrogen is added. In an atmosphere, heat treatment was performed by heating for 4 hours in a temperature range from the liquid phase formation temperature of the auxiliary agent to the firing temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat engine component such as a gas turbine rotor or a turbocharger rotor, particularly a silicon nitride component such as a complex-shaped component having a polished portion and a burnt surface where polishing is difficult. The present invention relates to a method for manufacturing a high quality sintered body.

[0002]

2. Description of the Related Art Conventionally, a silicon nitride sintered body is more stable than a metal at high temperatures, and is excellent in oxidation resistance and creep resistance. Therefore, it has been used for engine parts such as turbine rotors. Research is being conducted.

However, the burned surface of the silicon nitride sintered body,
That is, there is a problem that the strength of the surface which is directly subjected to heat during firing is reduced due to defects due to volatilization of the auxiliary component during firing, processing scratches during raw processing and the like. Therefore, in the past, a shape that can be polished has been dealt with by polishing, but a scratch that occurs during polishing or a structural part having a three-dimensional shape that is difficult to polish is different. Measures were needed.

For example, a technique has been proposed for dealing with the above-described polishing scratches and complicated shaped products by obtaining a healing effect by heat treatment in an oxidizing atmosphere. That is, as a means for recovering the burnt surface strength that has been reduced due to the surface scratches caused by the processing scratches on the polished surface and the volatilization of the auxiliary agent on the burnt surface, a technique of heat treatment at 600 to 1000 ° C. in an oxidizing atmosphere is known. Proposed (JP-A-6-8046)
No. 9).

[0005]

In the above method, although the healing effect for defects caused by polishing scratches and volatilization of the auxiliary agent is certainly obtained by the heat treatment in an oxidizing atmosphere, the heat treatment at the low temperature The auxiliary component is separated into a crystallized part and a melted part, and the auxiliary component becomes non-uniform, resulting in another problem that the high temperature strength inside the sintered body (internal high temperature strength) decreases. Will end up.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to maintain the healing effect against scratches and defects of the silicon nitride sintered material and to increase the internal high temperature strength. An object of the present invention is to provide a method for producing a quality sintered body.

[0007]

In order to achieve the above object, the invention of claim 1 is a method for producing a silicon nitride sintered body containing a component of an auxiliary agent for sintering. After that, heat treatment is carried out in an oxidizing atmosphere, and further in a temperature range not lower than the liquid phase generation temperature of the auxiliary agent and not higher than the firing temperature of the sintered body,
The gist is a method for manufacturing a silicon nitride sintered body, which is characterized by performing heat treatment again in a non-oxidizing atmosphere.

Examples of the auxiliary include rare earth oxides, but the scope of the present invention is a silicon nitride sintered body containing no rare earth oxide. As the conditions for the heat treatment in the oxidizing atmosphere, for example, a temperature of 1000 to 1400 ° C. and a heating time of 4 to 8 hours can be adopted.

As the conditions for the heat treatment in a non-oxidizing atmosphere, the liquid phase formation temperature differs depending on the auxiliary component, and therefore the heat treatment temperature is appropriately set according to the auxiliary component (type and addition amount of auxiliary agent). Although it can be set, a range higher than the liquidus formation temperature by 50 ° C. or more is suitable, and for example, a temperature of 1500
˜1850 ° C. and a heating time of 4 to 12 hours can be preferably adopted.

A second aspect of the present invention provides a method of manufacturing a silicon nitride sintered body according to the first aspect, characterized in that a rare earth oxide is used as the auxiliary agent. Examples of the rare earth oxide include Yb ₂ O ₃ and Y _{2
O 3, Er 2 O 3,} La 2 O 3, Tm 2 O 3, Sc 2 O 3, Dy 2
O ₃ , Ho ₂ O ₃ or the like can be adopted, and a compound of a rare earth oxide and silicon oxide may be used.

The addition amount of this rare earth oxide is 4
A range of up to 16% by weight can be adopted. The invention of claim 3 is
As the auxiliary agent, in addition to the rare earth oxide, Si
The gist of the method for producing a silicon nitride sintered body according to claim 2 is to use at least one of O ₂ , an Al compound, a 5a group oxide, and a 6a group oxide.

As an auxiliary agent other than the rare earth oxide,
For example, AlN, Al ₂ O ₃ , V ₂ O ₅ , WO ₃ , SiO ₂ ,
_{Nb 2 O 5, Ta 2 O} 5, Cr 2 O 3, can be adopted MoO ₂ and the like. Incidentally, when SiO ₂ is contained in the silicon nitride raw material, it may be used as an auxiliary agent.

The amount of the auxiliary agent other than the rare earth oxide added may be in the range of 0 to 10% by weight. Therefore,
The total addition amount of the auxiliary agent including the rare earth oxide is 4 to 2
A range of 6% by weight can be adopted. A fourth aspect of the present invention provides a method for manufacturing a silicon nitride sintered body according to any one of the first to third aspects, wherein a nitrogen atmosphere is used as the non-oxidizing atmosphere.

[0014]

DETAILED DESCRIPTION OF THE INVENTION As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a silicon nitride sintered body that has been heat-treated in an oxidizing atmosphere has a temperature above the liquidus formation temperature of an auxiliary agent. It was found that the internal high temperature strength is recovered while maintaining the healing effect against scratches and defects by performing heat treatment again in a non-oxidizing atmosphere in a temperature range below the firing temperature of the sintered body, and completed the present invention. did.

That is, according to the first aspect of the invention, first, the silicon nitride sintered body is first placed in an oxidizing atmosphere (usually at a relatively low temperature).
By heat treatment, it is possible to remove scratches and defects on the surface of the sintered body (burnt surface) (healing effect). During the heating, the auxiliary component agglomerates and causes a decrease in internal strength.However, in the next step, the auxiliary component is heat-treated at the above-mentioned predetermined temperature in a non-oxidizing atmosphere. Since such a liquid phase is generated, the coagulated auxiliary component diffuses during the heat treatment in the oxidizing atmosphere. This reduces the ubiquity of the auxiliary component inside the sintered body, thereby promoting the homogenization of the structure of the sintered body, and thus the internal strength,
In particular, the internal high temperature strength is restored.

On the other hand, when heated at a temperature lower than the liquid phase formation temperature, the internal high temperature strength is not recovered because the aggregated auxiliary component does not diffuse, and at a temperature higher than the firing temperature. When heated, grain growth of silicon nitride occurs, so that the characteristics of the silicon nitride sintered body deteriorate.

Further, in the invention of claim 2, as an auxiliary agent,
Rare earth oxide is used. When this rare earth oxide is used, it exhibits the effect of improving the sinterability during sintering. However, in the present invention, when the auxiliary agent is a rare earth oxide, the auxiliary agent is formed by liquid phase formation. It is advantageous in that the diffusion of the components easily proceeds.

In the third aspect of the invention, SiO ₂ , Al compounds, 5a group oxides and 6a group oxides can be used in addition to the rare earth oxides. Of these, SiO ₂ and A
The action of the 1 compound is to improve the sinterability, and the actions of the group 5a oxide and the group 6a oxide are to improve the sinterability and the creep resistance.

According to the fourth aspect of the invention, since the nitrogen atmosphere is used as the non-oxidizing atmosphere, there is an advantage that the decomposition of silicon nitride is suppressed. Note that, in addition to nitrogen, an atmosphere such as argon can be used, but it is preferable to include nitrogen at a nitrogen partial pressure that suppresses decomposition of silicon nitride.

[0020]

EXAMPLES Examples of the method for producing a silicon nitride sintered body of the present invention will be described below. (Example) Si ₃ having an average particle size of 0.75 μm and an α ratio of 95%
The N ₄ powder, rare earth oxide having an average particle diameter of 1 to 3 [mu] m (Yb ₂
0 ₃ , Y ₂ 0 ₃ , Er ₂ O ₃ ) and Al compounds (AlN, Al ₂
0 _8), 5a group element oxide (V ₂ O _5), 6a group element oxide (WO _3), or the like, for example, wet mixed with a composition such as shown in the following Table 1, was dried in a spray dryer. After the obtained powder is isostatically pressed under a pressure of 4 tons into a 60 mm square × 25 mm thickness, it is sintered by normal pressure sintering or hot isostatic pressing, for example, a firing temperature of 1600 to 1850 ° C. Was fired to obtain a sintered body. In addition to this sintering method, gas pressure sintering or a sintering method combining these can be adopted.

The obtained sintered body is first subjected to, for example, 1100 in an oxidizing atmosphere in order to obtain a healing effect.
Heat treatment is performed by heating at a relatively low temperature of ˜1300 ° C. for 8 hours, and thereafter, in order to improve internal high temperature strength, in a nitrogen atmosphere, at a temperature higher than the oxidizing atmosphere, that is, a liquid phase formation temperature of the auxiliary agent In the temperature range above and below the firing temperature, for example (depending on the composition) 1600 to 1800 ° C.
Was heat-treated by heating for 4 hours.

As a result, a silicon nitride sintered body having a healing effect and an improved internal high temperature strength was obtained. (Experimental Example) Next, an experimental example performed for confirming the effects of the above-described embodiment will be described.

Internal Strength Test 3 pieces of the sintered body fired at the composition and firing temperature shown in Table 1 were used.
For a test piece that was processed into a size of 4 mm × 4 mm × 40 mm and then heat-treated in the front and rear two steps under the conditions shown in Table 1,
SR-1601 (4-point bending test at room temperature), JIS
According to R-1604 (4-point bending test at high temperature of 1100 ° C.), the burnt surface was removed and an internal strength test (fold test) was performed. The results are shown in Table 1 as internal room temperature strength and internal high temperature strength.

Healing test 3 pieces of the sintered body fired at the composition and firing temperature shown in Table 1 were used.
mm × 4 mm × 40 mm to fabricate a test piece, and a diamond indenter is used for the tensile surface (during the bending test) of the test piece (load; 10 kgf, speed; 15 se)
c) A scratch of about 250 μm was made, and thereafter, heat treatment was similarly performed under the conditions shown in Table 1 and an internal strength test was similarly performed at room temperature. The results are shown in Table 1 as the internal room temperature strength. In the healing test, since the surface from which the burnt surface was removed was scratched, the internal room temperature strength was used.

Also, for those outside the scope of the present invention,
Similarly, a sintered body was prepared, and an internal strength test and a healing test were performed. The results are also shown in Table 1. In addition, in the following Table 1, it is divided into four groups according to the auxiliary agent and the firing temperature (first group; sample No. 1 to 1).
5, second group; sample Nos. 6 to 10, third group;
Sample Nos. 11 to 13, fourth group; Sample Nos. 14 to 1
5). Among them, sample No. 1, 6, 7, 11, 14
It corresponds to the Examples within the scope of the present invention, Sample N
o.2 to 5,8 to 10,12,13,15,16 correspond to comparative examples outside the scope of the present invention. Further, the samples Nos. 3, 8, 12, and 15 of the comparative example are those which are not annealed (heat treatment) at all, and the samples Nos. 2, 9, 10, and 1
Nos. 3 and 16 are only heat-treated in an oxidizing atmosphere, sample N
o.4 is the one in which the heat treatment temperature in the nitrogen atmosphere is lower than the liquid phase formation temperature after the heat treatment in the oxygen atmosphere, Sample No. 5
Indicates that the heat treatment temperature in the nitrogen atmosphere exceeds the firing temperature.

Of the samples in Table 1, sample Nos. 6 to 1
0 and sample Nos. 11 to 13 are those subjected to atmospheric pressure sintering, and sample Nos. 1 to 5 and sample Nos. 14 to 16 are those subjected to hot isostatic pressing.

[0027]

[Table 1]

As is apparent from Table 1, in the first group, the sample No. 1 of this example is the sample No. 1 of the comparative example.
Compared with Nos. 2, 4, and 5, the internal high-temperature strength and the healing effect were excellent. Sample No. 3 of the comparative example
Although the internal high temperature strength is higher than that of the example, since it is not heat-treated in an oxidizing atmosphere, there is no healing effect on scratches and defects, which is not preferable. In addition, the sample N of the comparative example
o.4 performs heat treatment in a nitrogen atmosphere, but the temperature is lower than the liquidus formation temperature, so the internal high temperature strength is low, and sample No. 5 of the comparative example performs heat treatment in a nitrogen atmosphere.
Since the temperature exceeds the firing temperature, grain growth occurs and the internal room temperature strength decreases.

In the second group, sample Nos. 6 and 7 of this example were excellent in internal high temperature strength and healing effect as compared with sample Nos. 9 and 10 of the comparative example. Although the sample No. 8 of the comparative example has a higher internal high temperature strength than the examples, it is not preferable because it has no healing effect because it is not heat-treated in an oxidizing atmosphere.

In the third group, sample No. 11 of this example was superior in internal high temperature strength and healing effect to sample No. 13 of the comparative example.
Although the sample No. 12 of the comparative example has higher internal high temperature strength than the examples, it is not preferable because it has no healing effect because it is not heat-treated in an oxidizing atmosphere.

In the fourth group, the sample No. 14 of this example had excellent internal high temperature strength as compared with the sample No. 16 of the comparative example. Incidentally, the sample No. of the comparative example.
Sample No. 15 has a higher internal high temperature strength than those of the examples, but it is not preferable because it has no healing effect because it is not heat-treated in an oxidizing atmosphere.

Needless to say, the present invention is not limited to the above-mentioned embodiments, and can be carried out in various modes without departing from the gist of the present invention.

[0033]

As described above in detail, according to the method for manufacturing a silicon nitride sintered body of the present invention, the sintered body is fired and then heat-treated in an oxidizing atmosphere. Since the heat treatment is performed again in a non-oxidizing atmosphere in a temperature range from the generation temperature to the firing temperature of the sintered body, the healing effect against scratches and defects of the silicon nitride sintered body is maintained and the internal high temperature strength is increased. There is a remarkable effect that can be done.

Claims (4)

[Claims] 1. A method for producing a silicon nitride-based sintered body containing a component of a sintering aid, which is followed by heat treatment in an oxidizing atmosphere after forming a sintered body by firing.
Further, the method for producing a silicon nitride sintered body is characterized by performing heat treatment again in a non-oxidizing atmosphere in a temperature range not lower than the liquid phase formation temperature of the auxiliary agent and not higher than the firing temperature of the sintered body. 2. The method for producing a silicon nitride sintered body according to claim 1, wherein a rare earth oxide is used as the auxiliary agent. 3. The auxiliary agent, in addition to the rare earth oxide, further contains SiO ₂ , an Al compound, a 5a group oxide and 6
The method for producing a silicon nitride sintered body according to claim 2, wherein at least one kind of group a oxide is used. 4. The method for producing a silicon nitride sintered body according to claim 1, wherein a nitrogen atmosphere is used as the non-oxidizing atmosphere.