TEM STUDY OF Y-DOPED ALPHA-SIALON COMPOSITE WITH 10 VOL-PERCENT TIN PARTICULATES

Microstructures of the 10 vol% TIN particulates added Y-doped alpha-Si AlON ceramic composites were studied by using TEM, HREM and EDS techni ques. alpha-SiAlON and TiN were the only main phases in this fully den se material. Less than 1 vol% amount of glass was detected and the maj ority of the glass was located at the triple grain boundary junction n odes while the boundaries remained clean. No reaction was noticed betw een the alpha' matrix and TIN particles, but some TiN particles, inclu ded within the matrix grains, were epitaxial with alpha-SiAlON. The ex tensive microcracking commonly existing around the very large TiN grai ns, due to the high thermal expansion mismatch between alpha' and TiN, was considered to have brought about negative effects on the strength of the composite materials and on toughening. The porosity and agglom eration of TIN particles resulting from local inhomogeneity of the liq uid during the sintering process further decreased the mechanical prop erties of the composites as they acted as cracking sources. Finally, p ossible processes were discussed for the improvement of the properties of alpha-SiAlON/TiN composites. (C) 1998 Elsevier Science B.V.