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, gamma domain boundary or gamma/gamma lamellar boundaries. Most of the Ti5Si3 nucleates at 1/2[1 (1) over bar0] super-dislocation networks, particularly at the extended nodes of [10 (1) over bar], where stacking faults exist, while some Ti5Si3 precipitates at 1/2[1 (1) over bar0] dislocations. In addition, most Ti5Si3 are precipitating out heterogeneously at pseudo-twin type gamma/gamma(p)* and 120degrees-rotational order-fault type gamma/gamma(R)* lamellar boundaries, but no Ti5Si3 is found to precipitate at true-twin type gamma/gamma(p)* lamellar boundaries, The growth mechanism of Ti5Si3 in TiAl is also studied. (C) 2002 Elsevier Science B.V. All rights reserved.