Effect of Ti content on the martensitic transformation in zirconia for Ti-ZrO2 composites

Ti-ZrO2 metal-ceramic composites with a series of graded compositions have been prepared by powder metallurgical process. The effect of Ti on the mart ensitic transformation in ZrO2 from tetragonal to monoclinic structure has been studied by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The experimental results show that the phases of the sint ered Ti-ZrO2 system composites are alpha -Ti, tetragonal zirconia (t-ZrO2) and monoclinic zirconia (m-ZrO2). The volume fraction of m-ZrO2 in ZrO2 inc reases with the increase of Ti content when the volume fraction of Ti is hi gher than 12.5vol.% in the Ti-ZrO2 composites. The nucleation of m-ZrO2 occ urs preferentially at the Ti-ZrO2 interface. The interfacial stress arising from the thermal expansion mismatch and the plastic deformation of Ti enha nce the driving force for the t-ZrO2-->m-ZrO2 transformation. It is noted t hat the content of Y2O3 stabilizing agent in ZrO2 should be increased as th e Ti content increases in the preparation of Ti-ZrO2 functionally graded ma terials (FGMs) to appropriately control the volume fraction of m-ZrO2. (C) 2001 Elsevier Science B.V. All rights reserved.