Peritectic Solidification Kinetics and Mechanical Property Enhancement in a Rapidly Solidified Ti–48 at% Al–8 at% Nb Alloy via Hierarchical Twin Microstructure

Abstract

The strength and ductility trade‐off dilemma has limited the wide application of TiAl‐based alloys. Here, a new insight into the potential for increasing the strength and ductility of a hypoperitectic Ti–48 at% Al–8 at% Nb alloy is accomplished by the electromagnetic levitation (EML) technique. Moreover, a systematic analysis of the primary and subsequent peritectic solidification kinetics is conducted in the undercooling range of 308 K. Assisted by a high‐speed camera, in situ observation of the liquid–solid (primary β‐Ti phase and peritectic α‐Ti phase) interface migration is accomplished. When the alloy melt is undercooled to 240 K, high‐ordered nanotwins are observed in the Ti–48 at% Al–8 at% Nb alloy, which form a unique hierarchical microstructure. Upon further increasing the undercooling, the density of these nanotwins is significantly enhanced. The room‐temperature compression results reveal that the strength and ductility increase up to 140% and 150%, respectively. This is mainly ascribed to the remarkable grain refinement, formation of nanotwins with various orientations, accumulation of dislocations and stacking faults, and retention of the metastable γ‐phase. The superior combination of strength and ductility indicates the possibility to fabricate high‐ordered nanotwins via rapid solidification, thus improving the performance of γ‐TiAl‐based alloys.