Lamellar boundary alignment of DS-processed TiAl-W alloys by a solidification procedure

Abstract

In this study, a beta solidification procedure was used to align the lamellae in a Ti-47Al-2W (at.%) alloy parallel to the growth direction. The Bridgman technique and the floating zone process were used for directional solidification. The mechanical properties of the directionally solidified alloy were evaluated in tension at room temperature and at 800 degrees C. At a growth rate of 30 mm/h (with the floating zone approach), the lamellae were well aligned parallel to the growth direction. The aligned lamellae yielded excellent room temperature tensile ductility. The tensile yield strength at 800 degrees C was similar to that at room temperature. The orientation of the gamma lamellar laths in the directionally solidified ingots, which were manufactured by means of a floating zone process, was identified with the aid of electron backscattered diffraction analysis. On the basis of this analysis, the preferred growth direction of the bcc-beta dendrites that formed at high temperatures close to the melting point was inferred to be [001](beta) at a growth rate of 30 mm/h and [111](beta) at a growth rate of 90 mm/h.