JPH0653610B2 - Manufacturing method of high toughness silicon nitride sintered body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a silicon nitride sintered body having high toughness, and is useful as various engineering parts such as mechanical parts and automobile parts as engineering ceramics.

[Conventional technology]

Several methods have been proposed so far for improving brittleness, which is an essential property of ceramics. The composite method is a typical method, and the fracture toughness can be improved by mixing and dispersing whiskers, fibers, particles and the like. For example, it is described in "Special Issue on Strengthening Ceramics", Ceramics Vol.21 NO.7, July, 1986, published by Ceramic Industry Association. At present, addition of whiskers seems to be the most effective for increasing the toughness of a silicon nitride sintered body.

[Problems to be Solved by the Invention]

However, a uniform dispersion is required to strengthen the composite. In particular, whiskers and fibers are difficult to disperse, and not only must they be mixed for a long time with a wet ball mill, but complete uniform dispersion is practically impossible. Also, molding methods such as slip casting and injection molding become difficult. Furthermore, it is difficult to sinter those containing whiskers and fibers, and even with the hot press method, it is not easy to bring the density close to the theoretical density.

The present invention intends to solve the above problems and to relatively easily obtain a high toughness silicon nitride sintered body.

[Means for Solving the Problems]

That is, the present invention is based on a silicon nitride powder having an average particle size of 1 μm or less as a main component, and an MgAl ₂ O ₄ —Al ₂ O ₃ -based sintering aid as 1 to 5% by volume as an average particle size of MgAl ₂ O ₄ minutes. Form a mixed raw material powder containing 3 to 10 μm of TiN powder 10 to 40% by volume.
This is a method for producing a high toughness silicon nitride sintered body, which is characterized by sintering.

The present invention will be described in more detail below.

As the main mechanism for improving fracture toughness by compounding, crack / diffusion, microcracking, stress-induced transformation, pullout, etc. are considered, but in the method of the present invention, crack / diffusion and microcracking are used. King is important. The crack day flexion causes energy to increase as the crack bends around the dispersed particles in a zigzag manner due to differences in the physical properties such as the toughness and the coefficient of thermal expansion of the matrix and the dispersed phase, and the interfacial state between the two. It is dissipated. Also, in microcracking, distortion occurs around the dispersed particles due to the difference in the coefficient of thermal expansion between the dispersed phase and the matrix, and a large number of cracks are generated. As a result, fine cracks are bonded to each other to grow, or new fine cracks are generated, so that the elastic modulus in this region is lowered. Therefore, the stress applied to the tip of the main crack is reduced.

As a result of various studies on the toughness of the silicon nitride sintered body, the present inventors found that TiN particles are optimal as the dispersed particles, and in order to disperse the TiN particles in the silicon nitride sintered body,
TiN powder having an average particle size of 3 to 10 μm was added to a mixed raw material powder consisting of silicon nitride powder, a sintering aid and TiN powder in an amount of 10 to 40
It was found that it is necessary to include the capacity%. Ti
If the average particle size of the N powder is less than 3 μm or exceeds 10 μm, it is not possible to achieve significant toughness, and
The content of TiN powder is 10 to 40% by volume in the mixed raw material powder.
Similarly, there is no significant improvement in toughness at other ratios,
In particular, if it exceeds 40% by volume, the strength will decrease.

The average particle size of the silicon nitride Si ₃ N ₄ powder used in the present invention is 1
It is necessary to be less than μm, and if it exceeds 1 μm, improvement in toughness is not recognized.

The sintering aid used in the present invention is a MgAl ₂ O ₄ -Al ₂ O ₃ -based one having MgAl ₂ O ₄ and Al ₂ O ₃ as the main components, and the amount used is in the mixed raw material powder, It is a ratio of 1 to 5% by volume as MgAl ₂ O ₄ minutes. As the proportion of Al ₂ O ₃ , in the mixed raw material powder,
It is preferably contained in an amount of about 0.2 to 5% by volume. Mg
The content of Al ₂ O ₄ -Al ₂ O ₃ based sintering aid is MgA in the mixed raw material powder.
If less than 1% by volume of l ₂ O ₄ , the sintering effect is small, and
If it exceeds 5% by volume, the strength will decrease. With a sintering aid different from the present invention, for example, an Al ₂ O ₃ —Y ₂ O ₃ -based sintering aid, high toughness cannot be achieved. In the present invention, MgO, MgSiO ₄ , M
gSiO ₃ , Mg (OH) ₂ , Mg (NO ₃ ) ₂ , MgSO ₄ , cordierite, etc.
It can also be used in combination with Mg compounds and further with sintering aids such as Y ₂ O ₃ , CoAl ₂ O ₄ , ZrO ₂ and SiO ₂ , the ratio of which is about 0.2 to 5% by volume in the mixed raw material powder. Is the content of.

The Si ₃ N ₄ powder, the MgAl ₂ O ₄ —Al ₂ O ₃ -based sintering aid and the TiN powder are mixed in a wet or dry manner using a mixer such as a ball mill. The forming / sintering method is not particularly limited, and normal pressure sintering, hot pressing, and HIP sintering can be adopted.

There are various methods for measuring the fracture toughness value K _IC , but in the present invention, IM
(Indentaion Micro fracture) method is adopted. this is,
"A survey research report on the standardization of fine ceramics entrusted by the Agency of Industrial Science and Technology, Ministry of International Trade and Industry in 1984, March 1985.
This is a measurement method described in "Monthly Fine Ceramics Association" and consists of four processes: mirror polishing of sample, indentation, indentation measurement, crack length measurement, and K _IC calculation using empirical formula.
That is, a Vitzkers indenter is pressed into the surface-polished sample. The device uses a Vitzkers or Knoop hardness tester. The length of cracks generated in the sample is measured using an optical microscope or SEM.

Although there are many empirical formulas for calculating K _IC , the following formula was used in the present invention.

(K _IC φ / Ha ^1/2 ) (H / E φ) ^2/5 = 0.129 (c / a) ^-3/2 E ... Young's modulus, H ... Hardness, a ... Indentation length, c ... Crack length, φ = 3, load 20 kg, load application time 15 seconds The fracture toughness value K _IC (MPa · m ^1/2 ) of various ceramics is generally Si ₃ N ₄ 4-6, SiC 3-5, Al ₂ O ₃ 3 ~ 5, partially stabilized ZrO ₂ (PSZ) 7 ~ 10, glass 0.75, WC-Co alloy 12 ~ 1
6. It is said to be aluminum alloy 34. According to the invention,
This can be increased to 8.5 or more by pressureless sintering.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 Various volume% sintering aids MgO, MgAl ₂ O ₄ , Al ₂ O shown in Table 1
₃ , Y ₂ O ₃ and 15% by volume of TiN powder having an average particle size of 4.0 μm as dispersed particles and a thermal expansion coefficient of 9.3 × 10 ⁻⁶ / ° C.
6 μm of Si ₃ N ₄ powder (SN-GD3 manufactured by Denki Kagaku Kogyo Co., Ltd.) was mixed to prepare 100% by volume of mixed raw material powder. A serpentine Si ₃ N ₄ sintered body was obtained by subjecting this to a pressureless sintering method of N ₂ 9 kg / cm ² at 1750 ° C. for 6 hours, and the fracture toughness value K _IC was measured. The results are shown in Table-1.

Example 2 In Experiment No. 9 of Table 1, TiN powder was mixed in various proportions.
Sintered bodies were prepared under the same conditions except that Si ₃ N ₄ powder was used instead, and the fracture toughness value K _IC was measured. The results are shown in Table-2.

Example 3 In Experiment No. 9 of Table-1, a sintered body was prepared under the same conditions except that the average particle size of Si ₃ N ₄ powder and TiN powder was changed as shown in Table-3, and fracture toughness was obtained. The room temperature bending strength of the value K _IC and JIS R1601 was measured. The results are shown in Table-3.

Example 4 In Experiment No. 9 of Table-1, a sintered body was prepared under the same conditions except that MgAl ₂ O ₄ powder was used in various proportions in place of Si ₃ N ₄ powder, and fracture toughness value K _IC was measured. The results are shown in Table-4.

The following can be understood from the above-described examples.

(1) From Example 1 and Example 4, when the addition amount of the MgAl ₂ O ₄ —Al ₂ O ₃ -based sintering aid was 1 to 5% by volume as MgAl ₂ O ₄ minutes, 8.5 MPa · A high K _IC of m ^1/2 or more can be obtained.

(2) From Example 2, when the TiN powder is 10 to 40% by volume, a high K _IC of 8.5 MPa · m ^1/2 or more can be obtained.

(3) From Example 3, when the average particle size of the Si ₃ N ₄ powder is 1 μm or less and the TiN powder has an average particle size of 3 to 10 μm,
A high K _IC of 8.6 MPa · m ^1/2 or more can be obtained.

〔The invention's effect〕

According to the present invention, a high toughness silicon nitride sintered body having a fracture toughness value of 8.5 MPa · m ^1/2 or more can be easily manufactured.

Claims (1)

[Claims] 1. A silicon nitride powder having an average particle diameter of 1 μm or less as a main component, and a MgAl ₂ O ₄ -Al ₂ O ₃ -based sintering aid as MgAl ₂ O ₄ min.
˜5% by volume and average particle size 3˜10 μm TiN powder 10˜4
A method for producing a high toughness silicon nitride sintered body, which comprises molding and sintering a mixed raw material powder containing 0% by volume.