PRESSURELESS SINTERING AND PHASE RELATIONSHIP OF SAMARIUM ALPHA-SIALONS

The sinterability of samarium alpha-sialon (alpha') compositions and t he phase assemblage around the alpha-sialon region have been studied. Samarium oxide is an effective stabiliser for alpha-sialons and has a significantly superior densification effect on alpha-sialon ceramics t han neodymium and yttrium oxides. The 21R polytypoid phase is found to be in equilibrium with Sm alpha-sialons instead of 12H as found in th e yttrium system. Two phase regions containing the alpha-sialon phase have been found, namely, alpha'-beta'-21 R-L (liquid) and alpha'-21R-2 7R-L. Compositions in the alpha'-beta'-21R-L region possess relatively more liquid phase than those in other alpha-sialon-containing phase r egions. With careful compositional selection, almost fully dense alpha -sialon ceramics can be prepared by pressureless sintering.