MULTIPHASE COMPOSITES OF TETRAGONAL ZIRCONIA AGGLOMERATE DISPERSED INTO ALUMINA AND ALUMINA-ZIRCONIA MATRICES

Multiphase composites of yttria- and ceria-doped tetragonal zirconia a gglomerates (10-50 mum) dispersed into an alumina or alumina-zirconia matrix were sintered at 1500-1600-degrees-C in air, followed by post-H ot Isostatic Pressing (HIP) at 1450-degrees-C and 150 MPa in an Ar gas atmosphere. The relative density of the recovered composites was abov e 98% of the theoretical density. By chemically etching on the surface of zirconia agglomerates, the sinterability of composites was apparen tly improved; and no microcracks nor pores were observed at the interf ace of agglomerate and matrix. According to scanning electron microsco py (SEM) observation, tetragonal and tetragonal monoclinic zirconia ag glomerates were highly dispersed into the alumina or alumina zirconia matrix. The multiphase composites containing 10 vol% spherical agglome rates demonstrate the relatively low value of bending strength, < 400 MPa, and a high value of fracture toughness, > 11 MPa m1/2. The crack propagation introduced by Vickers indentation was efficiently suppress ed and deflected by the agglomerates.