JPS63206358A - Manufacture of silicon nitride sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a silicon nitride sintered body having excellent high-temperature strength, and more specifically, to a method for manufacturing a silicon nitride sintered body having excellent high-temperature strength.
Pressing (abbreviated as "HP") relates to a method of manufacturing a silicon nitride sintered body having excellent wear resistance and mechanical strength and suitable as a sliding member of a bearing member.

(Prior Art) In recent years, ceramic sintered bodies have been actively used in gas turbine engine parts, high-precision parts, bearing parts, etc. for the purpose of improving thermal efficiency, saving fuel, reducing pollution, and reducing weight.

Among these ceramic sintered bodies, silicon nitride (Si3N4) is attracting attention as one of the most promising materials that has sufficient strength at high temperatures, is chemically stable, and is resistant to thermal shock.

Pressure sintering is the most well-known method for sintering silicon nitride to make it more dense and using a small amount of sintering aid. This pressure sintering method is a method in which silicon nitride raw material powder and a sintering aid are mixed in advance, the resulting compact is placed in a carbon goose case, and sintered while pressurized in the -axial direction. Compared to the normal pressure sintering method under atmospheric pressure, the sintered body produced using this method has the following characteristics: i) the densification temperature during sintering is lower, and ii) the sintered body becomes more uniform as the sintering temperature decreases. It has the advantage that a sintered body having a small particle size and a theoretical density can be produced in a short time.

(Problems to be Solved by the Invention) However, as a result of experiments conducted by the present inventors in accordance with this pressure sintering method, - Even if the compression press pressure in the axial direction was increased, the produced nitride Four-point bending strength JI of silicon sintered bodies
SR1601-1981) did not exceed 1000 MPa.

The purpose of the present invention is to achieve excellent wear resistance by using a pressure sintering method.
It is an object of the present invention to provide a method for manufacturing a silicon nitride sintered body having excellent mechanical strength.

(Means for Solving the Problems) The method for producing silicon nitride of the present invention includes a shrinkage start temperature and a shrinkage completion temperature of the silicon nitride powder compact when pressurizing and sintering the sinterable silicon nitride powder compact. The method is characterized in that the amount of pressure is increased between the two steps, and the maximum amount of pressure is applied to perform sintering.

(Function) As a result of investigating the relationship between the pressurizing temperature during hot pressing and the shrinkage rate of the sintered object, the present invention found that when the sintered object is hot pressed with a constant amount of pressure, the sintered object The shrinkage curve was created based on the fact that the material draws a curve that changes rapidly in a certain temperature range, that is, it shrinks rapidly in a certain temperature range.

Generally, in the hot press method, the maximum pressure P that can be applied is defined by the following equation based on the tensile strength of the goo case.

■ Here, δt: Tensile strength of the die case D: Outer diameter of the die case d: Inner diameter of the die case L: Length of the die case in the compression direction β: Length of the sample in the compression direction S Two safety factors (constant) k: Side pressure Ratio (constant) As is clear from the above formula, if l of the sample becomes smaller,
It can be seen that the maximum pressure P can be increased.

Therefore, when the sample contracts, the maximum pressure P that can be applied can be increased in accordance with the amount of contraction. That is, during hot pressing, applying pressure between the shrinkage start temperature and the shrinkage completion temperature of the sample has the advantage that higher pressure can be applied, and the sample after sintering also becomes more dense. By the way, the reason why we decided not to apply pressure after the shrinkage is complete is that after the shrinkage is complete, most of the material used as a sintering agent near the surface of the sample has been scattered and has lost its fluidity. This is because if a sample that has lost its surface fluidity is pressurized, it may cause cracks or fractures, and there is also a risk that the desired molded shape may not be obtained due to shrinkage.

(Example) The present invention will be explained in detail below.

Si, N, powder 100% by weight of average particle size IAtm,
5r00.5% by weight, Mg02% by weight, CeO□2.5
Add and mix in the proportion of 200 M
Rubber press molded with a molding pressure of Pa! =100mm
Seven specimens 1 of Hot press sintered.

(A) Maximum pressure that can be applied to this sample from the beginning in a nitrogen atmosphere: 29 MPa (300 kg f/cnf)
was applied, the temperature was raised to 1750° C. at a rate of 500° C./hr, and the temperature was maintained for 1.0 hour for sintering. The shrinkage rate of the sample at this time was also measured, and it was confirmed that the shrinkage start point and shrinkage completion point of the sample were 1200° C. and 1700° C., respectively (see FIG. 1 (Δ)).

(B) Increase the temperature to around 1200℃ in a nitrogen atmosphere (50℃)
The temperature was raised at a rate of 0 t/hr, a pressure of approximately 29 MPa was applied at a temperature of 1260°C, and then the temperature was increased to 1750°C at a rate of 500°C/hr.
The temperature was raised for 1.0 hours and sintered by holding for 1.0 hours (Fig. 1 (
B)).

(C) Under a nitrogen atmosphere, the temperature is raised to 1400℃ for 500 tons
After that, the temperature was raised to 1750°C at a rate of 500°C/hr and sintered by holding for 1.0 hours (Figure 1 (C)). ).

(D) Under a nitrogen atmosphere, increase the temperature to around 1700℃ for 50 minutes.
The temperature was increased at a rate of 0°C/hr, a pressure of approximately 29 MPa was applied at a temperature of 1615°C, and then the temperature was increased to 1750°C at a rate of 500°C/hr.
The temperature was raised for 1.0 hours and sintered by holding for 1.0 hours (Fig. 1 (
D)).

(E) Temperature 500℃ to 1740℃ under nitrogen atmosphere
/hr, and at this temperature, a pressure of about 29 MPa was applied, and then the temperature was raised to 1750°C at a rate of 500 t/hr, and sintered by holding for 1.0 hour (Fig. 1 (E)). .

(F) Temperature 500℃ to 1300℃ under nitrogen atmosphere
/hr, and from this temperature 0.145 MPa /hr.
The pressure was increased at 500 t/hr, and the temperature was increased at 500°C/hr. After 1500°C, the pressure was maintained at about 29 MPa and the temperature was increased at 500 t/hr until 1750°C.
The temperature was raised at 1.0 h and sintered by holding for 1.0 h (Fig. 1 (
F)).

(G) Apply a pressure of 10 MPa from room temperature under a nitrogen atmosphere, and raise the temperature to 1300°C at a rate of 500°C/hr for 10
A pressure of MPa was maintained. 0. after reaching 1300℃.
The pressure was increased to 095MPa/t and the temperature was also increased to 500MPa/t.
Raise the temperature at a rate of ℃/h, and after 1500℃, increase the pressure to about 29MP.
The temperature was raised to 1750° C. at a rate of 500° C./hr and held for 1.0 hours for sintering (Fig. 1 (G)).

JI
A four-point bending strength test piece was cut out according to SR-1601r Fine Ceramics Bending Strength Test Method and its room temperature strength was measured, and the results shown in Table 1 below were obtained.

Table 1 It is clear from Table 1 above that pressure is applied at a temperature before the contraction start point and after the contraction completion point of the sample, and a higher pressure than before is applied between the temperature immediately after the contraction start point and just before the contraction completion point of the sample. It can be seen that the numerical values of samples A and E to which no voltage was applied are low. Further, the strength of samples B and D, in which pressure was applied at a temperature immediately before the contraction start point and immediately before the contraction completion point of the sample, is smaller than that of sample C, in which pressure was applied at a temperature in the middle of the contraction process. Furthermore, the sample F, in which the pressure was gradually increased in a region where the shrinkage was particularly large, as the sample contracted, had the highest bending strength in this example. Also, if a constant pressure is applied before contraction starts, as in example (G),
If the pressure is at a level that does not adversely affect the sintered body, a sintered body with high strength can be obtained by increasing the pressure between the temperature at which contraction begins and the temperature at which contraction ends. The reason for this high bending strength is that when the maximum pressure is applied to the silicon nitride needle crystals in the silicon nitride sintered body before the compact starts shrinking, these needle crystals are sintered. While they are arranged randomly in the body, when (maximum) pressure is applied during contraction of the compact, the crystalline arrangement of the needle-like crystals tends to be closely aligned, which is thought to increase the bending strength. .

The temperature immediately after the contraction start point of the sample is, for example, approximately 105% of the temperature at the sample contraction start point, and the temperature immediately before the sample contraction completion point is, for example, the temperature at the sample contraction completion point. The temperature is preferably about 95% of the temperature.

(Effects of the Invention) According to the method for producing a silicon nitride sintered body of the present invention, it is possible to apply a greater pressure than before, and the pressure is applied while the silicon nitride powder or molded body is shrinking. Since the pressure is applied, the crystal directions of the needle crystals in the silicon nitride sintered body are aligned, and the sintered body is dense, so there is an advantage that a high-strength silicon nitride sintered body can be obtained.

[Brief explanation of the drawing]

Figure 1 (A) is an explanatory diagram showing the conventional hot pressing method and the amount of shrinkage of the sample. Figures 1 (B) to (F) are diagrams showing the shrinkage process of the sample when the temperature at which the pressure is applied is changed. FIG. 2 is a schematic diagram showing the main parts of the hot press machine. 1... Sample 2... Formwork procedure
Amendment (formality) May 12, 1988 Commissioner of the Patent Office Black 1) Akio Tono 1, Indication of the case Patent Application No. 35923 of 1988 3, Person making the amendment Relationship to the case Patent applicant 4, Agent 7, Contents of amendment (as attached) 1. [Figures 1 (B) to (F)] on page 10, line 14 of the specification
” should be corrected to “Fig. 1 (B) to (G).” Representative patent attorney Akira Sugimura Hidegai 1 person

Claims (1)

[Claims] 1. When pressurizing and sintering the silicon nitride powder compact, the amount of pressure is increased between the shrinkage start temperature and the shrinkage completion temperature of the silicon nitride powder compact, and the maximum amount of pressure is applied for sintering. A method for producing a silicon nitride sintered body, characterized by: