Reversible α′ ↔ β′ transformation in a textured Sm-sialon ceramic

A preferential orientation was observed in a Sm-sialon ceramic, of the composition Sm0.4Si9.6Al2.4O1.2N14.8, after hot pressing at 1800 °C for 2 h. Post-sintering heat treatment was performed at 1450 °C for 384 h, resulting in the forward α′ → β′ transformation, accompanied by the formation of M′SS and an increase in the 21R phase. Subsequent heat treatment at 1800 °C for 2 h resulted in the reverse β′ → α′ transformation, with a corresponding decrease in the M′SS and 21R phases. This confirms the fully reversible reaction of α′+liquid↔β′+M′SS+21R in Sm-sialon ceramics. In addition, the texture introduced by hot pressing was maintained after all heat treatments, indicating that there is a crystallographic relationship between the transformation phases. The microstructure and mechanical properties were also found to be mostly reversible, contrary to the behaviour of the α′ lattice parameters and bulk density.