JPS63282163A - Production of high-toughness silicon nitride ceramics - Google Patents

Abstract

PURPOSE:To obtain high-toughness Si3N4 type ceramics by molding metallic Si powder added with Si3N4 whiskers, then subjecting the molding to reaction nitriding and calcination. CONSTITUTION:An org. binder is added to the starting raw material prepd. by adding and mixing (B) 5-30wt.% Si3N4 whiskers and, if necessary, (C) 2-30wt.% sintering assistant such as Y2O3, MgO and spinel to and with (A) metallic silicon powder and after the mixture is thoroughly mixed, the mixture is molded and degreased. This degreased molding is subjected to the reaction nitriding for about 2hr at 1,300-1,500 deg.C in an N2 atmosphere, then to the regular calcination for about 3hr at 1,700-1,900 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A highly tough silicon nitride ceramic can be obtained by reactively nitriding a metal silicon powder compact to which silicon nitride whiskers have been added and then subjecting it to main firing.

[Industrial application field]

The present invention relates to a method for manufacturing and using high toughness silicon nitride ceramics.

[Prior art and problems to be solved by the invention] Silicon nitride ceramics have excellent characteristics such as high high temperature strength, hardness, and wear resistance, and are expected to be used as new structural materials. However, since ceramics are inherently brittle materials, their strength strongly depends on minute defects, and their strength tends to vary, making it difficult to ensure product reliability, and their widespread use has been delayed.

A method of adding whiskers, particularly silicon carbide whiskers, to improve the toughness of silicon nitride ceramics is known, but the achieved toughness is still not sufficient and further improvements are desired.

[Means for solving problems]

In order to solve the above problems, the present invention molds a mixture of metal silicon powder and silicon nitride whiskers,
The present invention provides a method for producing high-toughness silicon nitride ceramics, which is characterized by carrying out reactive nitriding and then main firing.

The starting material is a mixture of metallic silicon powder, silicon nitride whiskers, and optionally a sintering aid such as yttrium oxide, magnesium oxide, or spinel.

The amount of silicon nitride whiskers added is generally 5 to 30% by weight, preferably 10 to 20% by weight, and the amount of sintering aid added is generally 2 to 30% by weight.

After adding an organic binder to the above starting materials, mixing well, molding, and degreasing, first
Bake at 0°C for about 2 hours. Through this firing, metallic silicon is nitrided to become silicon nitride and sintered, but the silicon nitride produced at this time intimately wets not only the silicon nitride itself but also the silicon nitride whiskers. This is thought to be the cause of increasing the toughness of the product.

The conditions for reactive nitriding can be similar to conventional reactive nitriding for producing silicon nitride sintered bodies from metallic silicon.

After reactive nitriding, main firing is performed at a temperature of 1700 to 1900° C. for about 3 hours. This is done to advance the sintering of the silicon nitride ceramic and increase its density. The firing conditions can be essentially the same as those for conventional silicon nitride sintering.

〔Example〕

10 g of ittria powder 1 silicon nitride whisker (average length 15 μm) to 80 g of fine metal silicon powder (average particle size 2 μm)
m1 aspect ratio 20) Log was added, 8 g of an organic binder was added to the mixture, and ball milling was performed for 2 hours. The obtained powder was bent for test specimens (40×4×3
mm).

After degreasing, the temperature was raised to 1400°C in a nitrogen atmosphere, held for 4 hours to cause reaction nitridation, and then further heated to 1800°C for 3
Main firing was carried out by holding for a certain period of time.

The obtained sintered body was measured for three-point bending strength and fracture toughness by the Vickers indentation method in accordance with JJSR1601.

As a comparative example, 80g of silicon nitride powder and Iatria 10
A mixture of g and 10 g of silicon nitride whiskers was compacted using the same method, degreased, and then heated in a nitrogen atmosphere for 18 g.
A sintered body was prepared by firing at 00°C for 3 hours, and the three-point bending strength and fracture toughness were similarly measured.

The results are shown in the table below.

Table [Effects of the Invention] According to the present invention, silicon nitride ceramics with improved toughness can be obtained compared to ceramics obtained by adding silicon nitride whiskers to silicon nitride powder and sintering the mixture.

Claims (1)

[Claims] 1. A method for producing high-toughness silicon nitride ceramics, which comprises molding a mixture of metallic silicon powder and adding silicon nitride whiskers, reacting and nitriding the mixture, and then firing the mixture.