JPH04317468A - SiC reinforced silicon nitride composite - Google Patents

Abstract

PURPOSE:To obtain a composite material having excellent fracture toughness and mechanical strength and suitable for a cutting tool, etc., by dispersing SiC whiskers whose average diameter and aspect ratio are within a specified range and elliptical SiC particles whose average diameter and aspect ratio are within a specified range. CONSTITUTION:Fine Si3N4 powder (A) is mixed with a sintering aid (B) such as Y2O3, SiC whiskers (C) having 0.3-1.2mum average diameter and 10-40 aspect ratio and elliptical SiC particles (D) having 2-10mum average diameter and 2-8 aspect ratio so that a produced composite material contains 5-40vol.% of the components C, D, preferably in 60:40-40:60 vol. ratio of C:D. The resulting mixture is dried, granulated and sintered by a hot press, etc., to produce an SiC reinforced silicon nitride composite material contg. 5-40vol.% of the components C, D uniformly dispersed in the structure of the silicon nitride matrix.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to SiC-reinforced silicon nitride composites having high fracture toughness and mechanical strength.

0002

[Prior Art] Ceramic materials such as silicon nitride are generally useful as various structural materials used at high temperatures because of their excellent mechanical strength, thermal and chemical stability, etc. However, the material has the disadvantage of poor toughness against fracture. In recent years, much research has been conducted to improve this fracture toughness, and as one means of doing so, many attempts have been proposed to combine various whisker reinforcing materials into a ceramic base material.

[0003] The improvement in toughness due to the composite of whiskers is due to the fact that the whiskers dispersed in the sintered structure of ceramics stop or suppress crack growth, increase fracture resistance by deflecting cracks (deflection effect), and pull out the whiskers. This is said to be because it functions effectively in energy absorption at the tip of the crack. However, it has been found that compounding a large amount of whiskers is effective in improving toughness, but it also reduces the strength of the material [J
．． Am. Ceram. Soc. , 72(5) 791-7
98 (1989), Ibid. Bull. 65(2)3
51-356 (1986)]. The reason for this is that when the blending amount of whiskers is increased, smooth sintering of the composite material is likely to be inhibited due to mutual aggregation of the whiskers.

[0004] Also, a research report on improving the toughness of silicon nitride material by simultaneously compounding SiC whiskers and particles [J
．． Am. Ceram. Soc. , 73 (3) 678-6
83 (1990)], but it has been shown that in this case as well, the material strength is lower than that of a simple silicon nitride material.

[0005]

Problems to be Solved by the Invention The present invention aims to improve the silicon nitride matrix material by adding Si to it without impairing the original strength of the material.
In order to improve toughness by combining C whiskers, SiC
The development was based on the knowledge that it is effective to create a structure in which oval SiC particles are dispersed together with whiskers.

[0006] Accordingly, an object of the present invention is to provide a SiC-reinforced silicon nitride composite material having a composition structure that has both excellent fracture toughness and mechanical strength.

[0007]

[Means for Solving the Problems] A SiC-reinforced silicon nitride composite material according to the present invention to achieve the above object includes SiC whiskers with an average diameter of 0.3 to 1.2 μm and an aspect ratio of 10 to 40. SiC elliptic particles with a diameter of 2 to 10 μm and an aspect ratio of 2 to 8 have a volume content (Vf) of 5 to 8.
The structural feature is a composition structure in which 40% of silicon nitride is homogeneously dispersed in a matrix structure.

[0008] SiC whiskers are a material that mainly contributes to improving strength, and have an average diameter of 0.3 to 1.2 μm.
, an aspect ratio of 10 to 40 is used. When the average diameter is less than 0.3 μm and the aspect ratio is less than 10, agglomeration tends to occur and it becomes difficult to obtain a homogeneous structure, and when the average diameter exceeds 1.2 μm, the strength improving function is reduced. Moreover, when the aspect ratio exceeds 40, the denseness of the structure decreases.

[0009] SiC elliptical particles are grains shaped like cocoons or rice grains, and are a material that functions to improve fracture toughness. The SiC elliptical particles have an average diameter of 2 to 10
It is important that the aspect ratio is 2 to 8,
If the average diameter is less than 2 μm and the aspect ratio is less than 2, the bridging effect and deflection effect will be insufficient and no improvement in toughness can be expected. On the other hand, if the average diameter is more than 10 μm and the aspect ratio is more than 8, the composite performance will be poor. Decline.

The SiC whiskers and SiC elliptical particles having the above properties have a volume content (
Vf) is homogeneously dispersed in the range of 5 to 40%, preferably 15 to 35%. If the volume content (Vf) is less than 5%, no composite effect will be produced, and if it is added in excess of 40%, no improvement in properties can be expected, but rather the sinterability will deteriorate.

[0011] At this time, it is desirable to set the blending ratio of SiC whiskers and SiC elliptical particles in a volume ratio of 60:40 to 40:60 in order to impart strength and toughness in a well-balanced manner.

[0012] The SiC reinforced silicon nitride composite material having such a composition structure has SiC whiskers having the above properties and SiC
Manufactured by a method in which elliptical particles are mixed with silicon nitride matrix powder so that the volume content (Vf) is 5 to 40%, and the mixture is sintered under normal pressure, uniaxial pressure, or isotropic pressure. can do. The conditions during sintering are N2 atmosphere.
It is non-oxidizing, such as, and sintered at a temperature range of 1,600 to 1,850°C.

[0013]

[Function] According to the present invention, SiC whiskers with specific properties are capable of crack deflection, pull-out, and
It functions to improve the fracture toughness of the composite material by a stress relaxation mechanism at the tip of a crack such as ll out), and to increase the structural strength by suppressing the grain growth of the matrix during composite sintering.

[0014] The SiC elliptical particles act to relieve local stress at the crack tip mainly based on bridging effect and deflation effect, and contribute to improving toughness. This effect is effective for elliptical particles, which exhibit a better effect than spherical or disk-shaped SiC particles. Moreover, mixing and filling of raw materials during production becomes smooth, and sinterability is also improved.

[0015] These effects and the balance function by volume content (Vf) work together to form a microstructure of the SiC-reinforced silicon nitride composite material that has both a high degree of fracture toughness and material strength.

[0016]

[Examples] Examples of the present invention will be explained below in comparison with comparative examples. Examples 1 to 8, Comparative Examples 1 to 5 5 each of Y2 O3 and Al2 O3 as sintering aids
% Si3N4 powder (manufactured by Ube Industries, Ltd., SN-E10) with an average particle diameter of 0.2 μm was used as a matrix, and SiC whiskers and SiC elliptical particles were added to it under the properties and conditions shown in Table 1, and ethanol was added. The mixture was placed in a ball mill and mixed thoroughly with wet stirring. In addition, comparative example 1
~2 is an example in which the properties of SiC elliptical particles deviate from the specific requirements of the present invention, Comparative Example 3 is a sintered body of silicon nitride alone, Comparative Example 4 is a composite material of only SiC whiskers, and Comparative Example 5 is a material made of a composite of only SiC whiskers.
This is a composite material made only of iC elliptical particles.

[0017]

The mixed slurry was dried and granulated by a spray drying method, and sintered using a hot press under the conditions of a nitrogen atmosphere of 600 Torr, a pressure of 400 kg/cm 2 , a temperature of 1750° C., and a time of 30 minutes. Each SiC obtained
The reinforced silicon nitride composite material was processed into a test piece, and its density (relative density), transverse rupture strength, and fracture toughness were measured, and the results are shown in Table 2. The transverse rupture strength is measured using the 3-point bending test method (JIS
1601), fracture toughness was determined using the IF method (load 20 kg, time 1
5 seconds, Hv), part of which was measured by the SEPB method.

[0019]

From the results in Table 2, it can be seen that the Examples having the composition structure of the present invention have improved strength and toughness compared to the Comparative Examples.

[0021]

As described above, according to the present invention, by using SiC whiskers and SiC elliptical particles together as reinforcing materials under specified conditions, high-grade SiC can be produced that has both excellent fracture toughness and mechanical strength. A reinforced silicon nitride composite can be provided. Therefore, it is useful for members such as cutting tools.

Claims (2)

[Claims] Claim 1: SiC whiskers with an average diameter of 0.3 to 1.2 μm and an aspect ratio of 10 to 40 and an average diameter of 2 to 40.
A SiC-reinforced silicon nitride composite material having a composition structure in which SiC elliptical particles having a diameter of 10 μm and an aspect ratio of 2 to 8 are homogeneously dispersed in a silicon nitride matrix structure at a volume content (Vf) of 5 to 40%. 2. The SiC-reinforced silicon nitride composite material according to claim 1, wherein the blending ratio of SiC whiskers and SiC elliptical particles is in the range of 60:40 to 40:60 by volume.