Hot pressed silicon nitride containing finely dispersed silicon carbide or silicon aluminum oxynitride

摘要

A hot-pressed silicon nitride product containing a finely dispersed silicon carbide mixture is described. The product has very high strength at room temperature as well as high strength at elevated temperature. It has a high density and its electrical conductivity can be controlled over several orders of magnitude. In preferred forms the electrical resistivity is on the order of 2-10 ohm centimeters and, accordingly, the product can be machined by electric discharge machining. Where high strength is desired the product can be made to have a transverse rupture strength in excess of 100,000 p.s.i. as measured by a four point test at room temperature and, at 1375 DEG C, the transverse rupture strength can be in excess of 40,000 p.s.i., as measured by a three point test. This high strength product is formed predominantly of an essentially continuous matrix of silicon nitride which, under a scanning electron microscope, appears to have an average crystal size less than 1 micron.