B2 precipitates and distribution of W in a Ti–47Al–2W–0.5Si alloy

The precipitation behavior of B2 particles and the distribution of W in a Ti–47Al–2W–0.5Si alloy were investigated using high-spatial resolution analytical electron microscopy (AEM) and high-resolution electron microscopy (HREM). The ledges at the α2/γ interfaces were found to be enriched in W and therefore the preferable nucleation sites for the B2 precipitates. In the B2 phase, as high as one third of Al is substituted by W in comparison with the composition of the γ phase. The segregation of W to the α2/γ and B2/γ interfaces was also detected. These results provide explanations for the previous observations that additions of tungsten are effective in promoting the creep resistance of TiAl alloys.