Enhanced Wear Performance of Transformation Toughened Ceramics by Microstructural Optimization

Abstract

The poor rolling/sliding wear performance of transformation toughened ceramics (TTC) such as partially stabilized zirconia (PSZ) is believed to be a result of the volume expansion accompanying phase transformation of precipitates located immediately beneath the contacting surface. The expanding precipitates induce a surface uplift leading to surface waviness and altered rolling/sliding conditions. The very same precipitates, on the other hand enhance the toughness of the ceramic by preventing the growth of surface cracks. In order to find a compromise solution, an optimization problem is formulated for an idealized model consisting of an edge crack normal to the contacting surface and a periodic distribution of transformable grains in the layer immediately beneath this surface. The objective is to maximize the crack tip shielding by varying the volume fraction and size of the layer without exceeding a prescribed allowable surface uplift. It is shown that the maximum volume fraction of t-ZrO2 is attained at a certain depth below the surface but that its magnitude is considerably smaller than that pertaining in peak-aged PSZ.