PARTIALLY STABILIZED ZIRCONIA CERAMICS; METHOD OF MAKING SAID CERAMICS, DIES CONSTRUCTED OF SAID CERAMICS, CUTTING TOOLS WITH A CUTTING SURFACE AND TAPPET FACINGS FORMED OF SAID CERAMICS

摘要

A magesia partially stabilised zirconia ceramic material possessing from about 2.8 to about 4.0 wt per cent magnesia, and made from a zirconia powder containing no more than about 0.03 per cent silica is described. The ceramic material has a microstructure, produced as a consequence of the method by which the material is made, which provides both high strength and good thermal shock resistance properties. This microstructure comprises grains of cubic stabilised zirconia within which are formed, during cooling from the firing temperature, precipitates of tetragonal zirconia. These precipitates are elliptical in shape, with a long axis of about 1500 Angstrom units. Additionally, some of the tetragonal zirconia precipitates are made to transform into a non-twinned microcrystalline monoclinic form of zirconia by reducing the temperature of the material to below 800 DEG C, then subsequently holding the material at a temperature in the range from 1000 DEG C to about 1400 DEG C. The ceramic material may also contain up to 36 wt per cent of hafnia. Such materials can be used for inter alia moulds, dies, tappet facings and cutting tools.