INFLUENCES OF SURFACE-ROUGHNESS AND PHASE-TRANSFORMATIONS INDUCED BY GRINDING ON THE STRENGTH OF ZRO2-Y2O3

It is clear that a tetragonal phase transforms to the monoclinic and r hombohedral phases in grinding of ZrO2 doped with 3 mol% Y2O3. The gri nding process also changes the roughness of the surface. Because surfa ce roughness and structural changes in the deformed surface layer shou ld influence the mechanical properties of ZrO2-Y2O3 the bending streng th sigma(b) of ground specimens is presented as a function of both the volume of martensitic transformed phase and the roughness of the surf ace. Then, sigma(b) is assumed to be equal to sigma(o)(1+epsilon(m+r)gamma), where sigma(o) is the original bending strength of the sintere d material polished to a surface roughness of 0.1 mu m, and epsilon(mr) and gamma are the degrees of influences caused by phase transformat ion and surface roughness. Furthermore, epsilon(m+r) and gamma were de fined respectively by the following equations of 1.71(V-m-1.3)/100 and -0.55(R(max)-0.1)/100, where V-m is the volumetric percentage (vol%) Of monoclinic phase, and R(max) is the roughness of the abraded surfac e. The bending strength increased as much as 2-14% because of phase tr ansformation and decreased as much as 2-5% because of an increase in s urface roughness. The degrees of influence of epsilon(m) and epsilon(r ) by both phase transformations were approximately 6 and 5.8%.