Micromechanics of deformation in porous liquid-phase-sintered alumina under Hertzian contact

A series of fine-grained porous alumina samples, with and without a liquid phase, were fabricated in compositions matched closely to commercially avai lable alumina used as microelectronic substrates. Hertzian indentation on m onolithic specimens of the glass-containing samples produced a greater quas i-ductile stress-strain response compared with that observed in the pure al umina. Maximum residual indentation depths, determined from surface profilo metry, correlated with the stress-strain results. Moreover, microstructural observations from bonded interface specimens revealed significantly more d amage in the form of microcracking and under extreme loading, pore collapse , in the glass-containing specimens. The absence of the typical twin faulti ng mechanism observed for larger-grained alumina suggests that the damage m echanism for quasi-ductility in these fine-grained porous aluminas was deri ved from the pores acting as a stress concentrator and the grain boundary g lass phase providing a weak path for short crack propagation.