Microstructure and heterogeneous nucleation phenomena in cast SiC particles reinforced magnesium composite

The microstructure and heterogeneous nucleation phenomena in cast SiC parti cles reinforced magnesium composite have been studied using optical and tra nsmission electron microscopy (TEM). The microstructure of magnesium compos ites showed that most SiC particles were pushed and segregated at the grain boundaries while few SIC particles (3%) were entrapped in the magnesium gr ain. The SiC particles in the magnesium composite were identified as 6H alp ha-SiC structure. Stacking faults and pits defects were also observed withi n the SiC particles. The primary magnesium phase which heterogeneously nucl eated on the SiC particle surface has been identified with a small lattice disregistry (2.3%) while their crystallographic orientation relationship wa s (1010)(Mg)//(0001)(SiC). Examination of the composite interface indicated that the eutectic and Cu5Zn8 phases were able to wet the SiC particles and heterogeneously nucleate on the SIC particles while the crystallographic o rientation relationships between them were (0111)(SiC)//(110)(Mg17A112) and (0001)(SiC)//(001)(Cu5Zn8), respectively. Finally, the factors that influe nce the heterogeneous nucleation of primary magnesium phase, eutectic and C u5Zn8 phases on the SiC particles are discussed. (C) 2000 Published by Else vier Science S.A.