Morphological evolution of banding structures at high solidification velocity

Laser rapid solidification experiments were performed on a Ti-53at.%Al hypoperitectic alloy to investigate the dendritic growth behavior near the limit of high velocity absolute stability. By adopting an improved sampling method of TEM, the growth morphology evolution of the laser-resolidified layer was observed directly. Higlivelocity banding structures was firstly detected in Ti-Al peritectic alloys. The high velocity banding structures are parallel to the solid-liquid interface and made of the oscillation structures grown alternatively in modes of cell and plane morphologies. In the light bands with cellular growth mode, all dislocation assembles parallel to the growth direction and forms cell boundaries; while all dislocation distributes randomly in the dark bands. The determined growth velocity range for the appearance of banding structures is 0.5-1.1 m/s and the origin of the banding structure agrees well with the prediction of the CGZK phenomenological model. (C) 2002 Elsevier Science B.V. All rights reserved.