NUCLEATION AND GROWTH OF ALPHA'-SIALON ON ALPHA-SI3N4

Morphology, composition, and growth defects of alpha'-SiAlON have been studied in a fine-grained material with an overall composition Y0.33Si10Al2O1N15 prepared from alpha-Si3N4, AlN, Al2O3, and Y2O3 powders. TEM analysis has shown that fully grown alpha'-SiAlON grains always contain an alpha-Si3N, core, implicating heterogeneous nucleation operating in the present system. The growth mode is epitaxial, despite the composition and lattice parameter difference between alpha-Si3N, and alpha'-SiAlON. The inversion boundary that separates two domains in the seed crystal is seen to continue in the grown alpha'-SiAlON. Lacking a special growth habit, the growth typically proceeds from more than one site on the seed crystal, and the different growth fronts impinge on each other to give an equiaxed appearance of alpha'-SiAlON. Misfit dislocations on the alpha/alpha' interface are identified as [0001] type (b = 5.62 angstrom) and 113 [1210BAR] type (b = 7.75 angstrom). These nucleation and growth characteristics dictate that microstructural control of alpha'-SiAlON must rest on the size distribution of the starting alpha-Si3N, powder.