Precipitation of Ti5Si3 phase in TiAl Alloys

The nucleation, growth and interface structure of Ti5Si3 precipitates in Ti52Al48–3Si, Ti52Al48–3Si2M (M=Cr, V), and Ti52Al48–3Si2Cr2V (at.%) alloys were studied. It is found that nucleation of Ti5Si3 precipitates depends on the dislocation types, γ domain boundary or γ/γ lamellar boundaries. Most of the Ti5Si3 nucleates at 1/2[101̄] super-dislocation networks, particularly at the extended nodes of [101̄], where stacking faults exist, while some Ti5Si3 precipitates at 1/2[11̄0] dislocations. In addition, most Ti5Si3 are precipitating out heterogeneously at pseudo-twin type γ/γp* and 120°-rotational order-fault type γ/γR* lamellar boundaries, but no Ti5Si3 is found to precipitate at true-twin type γ/γT* lamellar boundaries. The growth mechanism of Ti5Si3 in TiAl is also studied.