High-resolution and analytic electron microscopy investigations on the microstructure of a TiAl (W, Si) alloy

The microstructure of a Ti-47Al-2W-0.5Si alloy has been investigated using high-resolution electron microscopy and analytical electron microscopy. Fro m the three main phases, i.e. gamma, alpha(2) and B2, many precipitates: ar e formed. Ti5Si3 particles formed in the equiaxed grains match well with th e gamma matrix. A new orientation relationship has been identified between the Ti5Si3 and gamma phase. Due to the stabilizing effect of W, B2 phase is formed in the alloy, and it contains much more W, more Si and shows a high er Ti to Al ratio in comparison with the equiaxed gamma phase. Moreover, th e gamma precipitates formed in the B2 phase contain small amounts of W and Si. In the (gamma + alpha(2)) lamellar structure, Ti5Si3 and B2 particles a re formed. The Ti5Si3 particles were formed mainly by the dissolution of th e preliminary B2 particles. This is atcributed to the enrichment of Si and the Ti to Al ratio in the B2 phase.