Nucleation and Growth of α′‐SiAlON on α‐Si ₃ N ₄

Morphology, composition, and growth defects of α′‐SiAION have been studied in a fine‐grained material with an overall composition Y 0.33 Si 10 Al 2 O 1 N 15 prepared from α‐Si 3 N 4 , AlN, Al 2 O 3 , and Y 2 O 3 powders. TEM analysis has shown that fully grown α′‐SiAloN grains always contain an α‐Si 3 N 4 core, implicating heterogeneous nucleation operating in the present system. The growth mode is epitaxial, despite the composition and lattice parameter difference between α‐Si 3 N 4 and α′‐SiAlON. The inversion boundary that separates two domains in the seed crystal is seen to continue in the grown α′‐SiAION. 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 α′‐SiAlON. Misfit dislocations on the α/α’interface are identified as [0001] type ( b = 5.62 Å) and 1/3 [1 2 10] type ( b = 7.75 Å). These nucleation and growth characteristics dictate that microstructural control of α′‐SiAlON must rest on the size distribution of the starting α‐Si 3 N 4 powder.