High-velocity banding structure in the laser-resolidified hypoperitectic Ti47Al53 alloy

Stability analysis of a growing solid/liquid interface is the fundamental concept of modern solidification theory. Here, serial laser rapid solidification experiments were performed on a hypoperitectic Ti47Al53 alloy to explore the dendritic growth behavior near the limit of high-velocity absolute stability. SEM and TEM techniques were carried out to investigate the microstructure and identify the phase composition. By adopting an improved sampling method of TEM, the growth morphology evolution of the laser-resolidified layer was observed directly and high-velocity banding structure was firstly detected in Ti-Al peritectic alloys. The high-velocity banding structures are parallel to the solid/ liquid interface (normal to the growth direction) and made of the oscillation structures grown alternatively in modes of cell and plane morphologies. In light bands with cellular growth mode, all dislocation assembles are parallel to the Growth direction and forms the cell boundaries, while all dislocation distributes randomly in dark bands. The determined growth velocity range for the appearance of high-velocity banding structures is about 0.5 similar to 1.1 m s(-1) according to the rapid solidification experiments, and the origin of the banding agrees well with the prediction of the CGZK phenomenological model (Acta Metal. Mater. 40 (1992) 983). (C) 2002 Elsevier Science B.V. All rights reserved.