A method of producing a silicon nitride ceramic component, comprising: grinding a silicon nitride sintered body comprising .alpha.--Si.sub.3 N.sub.4 having an average grain size of 0.5 .mu.m or smaller and .beta.'-sialon having an average grain size of 3 .mu.m or smaller in major axis and 1 .mu.m or smaller in minor axis into a predetermined size with a surface roughness of 1-7 .mu.m in ten-point mean roughness; heat treating the same at temperature range of 800.degree.-1200.degree. C. in the air; and standing it to allow to be cooled, whereby providing a residual stress in the ground surface before and after the heat treating as a residual compressive stress at a ratio of 1 or higher of the residual compressive stress after the heat treating to that before the heat treating (residual compressive stress after the heat treating/residual compressive stress before the heat treating), preferably 5 or more.

The present invention provides a silicon nitride-based sintered body having excellent mechanical properties from room temperature to a medium-low temperature range, a low friction coefficient and excellent wear resistance; a raw material powder for the sintered body; a method of producing the raw material powder; and a method of producing the sintered body.The sintered body of the present invention comprises silicon nitride, titanium compounds and boron nitride, or else silicon nitride, a titanium-based nitride and/or carbide, silicon carbide and graphite and/or carbon; and it has a mean particle diameter of 100 nm or less, and a friction coefficient under lubricant-free conditions of 0.3 or less, or else 0.2 or less. The silicon nitride-based composite powder, which is the raw material of the sintered body comprises primary particles of each of silicon nitride and titanium compounds, containing boron or carbon, each having a mean particle diameter of 20 nm or less, or 30 nm or less, and a phase containing an amorphous phase that surrounds the surfaces of the primary particles. Moreover, the method of producing the sintered body comprises pulverizing and mixing a silicon nitride powder, a sintering aid powder, a metallic titanium powder and a boron nitride powder, or else a silicon nitride powder, a sintering aid powder, a metallic titanium powder and a graphite and/or carbon powder, until the mean particle diameters become 20 nm or less, or else 30 nm or less, thus forming secondary

The present invention provides a silicon nitride based sintered body having excellent mechanical properties from room temperature to a medium low temperature range, a low friction coefficient and excellent wear resistance. The sintered body comprises silicon nitride, titanium compounds and boron nitride or silicon nitride, titanium based nitride and/or carbide, silicon carbide and graphite and/or carbon; and has a mean particle diameter of 100 nm or less and a friction coefficient under lubricant free conditions of 0.3 or less.

In the production of a silicon nitride sintered body through a hot press method, a sintering aid protecting agent is added to the raw material. The employable protecting agents are metallic elements such as Ta, W and Mo and compounds of the metallic elements such as nitrides and silicides. Conversion of these elements and compounds to carbides occurs preferentially to reduction of the sintering aid. Thus, it becomes possible to suppress reduction of the sintering aid in a reducing atmosphere formed, for example, of carbon monoxide, which is generated particularly when a graphite pressing die is employed.

There is disclosed a silicon nitride sintered body produced by sintering a molded article which comprises a mixture of a silicon nitride powder as the main component and plural kinds of sintering additives, wherein said silicon nitride powder is set to be 0.1 to 1.0 .mu.m in average grain size, and said plural kinds of sintering additives includes first and second sintering additives, said first sintering additive comprising oxide powders of at least one element of Group 3a element, said second sintering additive comprising oxide powders of at least one element selected from Zr (zirconium), Hf (hafnium), Nb (niobium), Ta (tantalum) and W (tungsten), said first sintering additive having the average grain size set to be 0.1 to 10 times as large as the average grain size of said silicon nitride powder and being incorporated in an amount ranging from 0.1 to 10% by weight to the mixture, said second sintering additive being such particles as that part of the particles are of grain size in the range from 10 to 100 times as large as the average grain size of said silicon nitride powder but the number of such part of the particles is in the 5 to 50% range of the total particle number and being incorporated in an amount ranging from 0 to 10% by weight to the mixture (provided that 0% by weight is not included). The sintering process of the molded article comprises a primary sintering in an atmosphere containing a nitrogen gas under the atmospheric pressure from 1 to 20 kgf/cm.sup.2 at 1600-1800.degree. C., and subsequently secondary sintering in an atmosphere containing a nitrogen gas under the atmospheric pressure ranging from 100 to 2000 kgf/cm.sup.2 at a temperature lower than that of primary sintering.