TOUGHENING EFFECTS OF WC CO PARTICLES AND COMPRESSIVE SURFACE STRESS ON (AL2O3 WC/CO) TIC/NI GRADED MATERIALS/

A graded material of the (Al2O3 WC/Co)/TiC/Ni was prepared by using th e self-propagating high-temperature synthesis-aided hot isostatic pres sing process. The WC/Co particles were added to the outer Al2O3 layer in order to activate the heterophase toughening effects and control th e thermal expansion mismatch between the outer and inner layers. SEM a nd TEM observations show a clustering structure of the WC/Co cermet in the Al2O3 matrix. The residual stress introduced by the compositional ly graded structures was analysed using FEM calculation and X-ray diff raction. Measurements of the indentation toughness and R-curve behavio ur indicated that the compressive surface stresses and WC/Co particles can significantly strengthen and toughen the Al2O3 ceramics. The inde ntation toughness of the (Al2O3 WC/Co)/TiC/Ni at the surface was 13.1 MPam(1/2), while those of the (Al2O3 WC/Co) uniform composite and the monolithic Al2O3 were 7.3 and 4.0 MPam(1/2), respectively. It was foun d by SEM observation of the crack propagation induced by indentation, that the crack deflection, bridging, blunting and arresting occurred a t the WC/Co clusters. (C) 1998 Chapman & Hall.