Deformation mechanisms in α-phase silicon nitride ceramics

Changes of phase composition and morphology were investigated in Si3N4 both before and after compressive deformation testing. Si3N4 specimens, with 5 wt% Y2O3 and 5 wt% MgAl2O4 additives, were rapidly consolidated to preserve the initial, metastable a-phase present in the Si3N4 starting powders. Constant strain rate compression tests were used to evaluate the strain rate dependency of the flow stress. At 1723 K, a flow stress dependency value of n = 2 was observed.