Dense silicion nitride ceramic containing fine grained titanium carbide, tungsten carbide or tantalum carbide

摘要

This invention relates to a sintered silicon nitride ceramic material comprising:
<UnorderedLists id="ula01" listStyle="none" compact="compact"><ListItem>a) at least 80 wt% silicon nitride grains, and</ListItem><ListItem>b) between 0.1 and 5 wt% additive grains characterized by at least one of :
<UnorderedLists id="ula02" listStyle="none" compact="compact"><ListItem>i)a Knoop hardness of at least 25 GPa,</ListItem><ListItem>ii) a coefficient of thermal expansion of at least 6 x 10<Sup>-6</Sup>/K, and</ListItem><ListItem>iii) a modulus of elasticity of at least 600 GPa,</ListItem></UnorderedLists></ListItem></UnorderedLists> wherein the maximum detectable grain size of the additive grains is no more than 4 um, as determined by a photomicrograph of a polished 75 mm<Sup>2</Sup> microstructure of the silicon nitride material.