Thermal Shock Resistance of Ceramic Cutting Tools

Abstract

Most ceramic materials are unsuited to conditions involving non-uniform temperature distributions because of their inherent brittleness. Ceramic cutting tools operate in conditions of rapid temperature variation and consequently thermal cracking is frequently observed. Under certain cutting conditions, these cracks are the major cause of tool failure. Thus, establishing the conditions under which thermal cracking occurs and identifying material parameters governing thermal shock resistance should lead to clearer ideas about how to develop thermal shock resistant ceramic cutting tool materials. Two tool materials, CC 620 (a pure ceramic containing Al2O3 and ZrO2) and CC650 (a mixed ceramic containing Al2O3 and Ti(N, C)), were used for evaluating thermal shock resistance, both by quenching from elevated temperature into cold water and by steel machining tests (SS 2541). It is shown that material parameters quantifying thermal shock resistance developed from simple quenching experiments, although frequently used, are not directly applicable when assessing thermal shock resistance in metal cutting conditions. This is mainly because of the presence of a region of superficial plastic deformation, ∼1μm deep, at the worn ceramic tool surface and of creep deformation during cutting under conditions severe enough to cause thermal cracking upon cooling. In addition, maximum cutting edge temperatures for a given set of cutting data differ with thermal conductivity of the tool material.