Stability of lamellar microstructure of hard orientated PST crystal of TiAl alloy

Microstructural changes were investigated quantitatively during the creep deformation of a hard oriented Ti-48Al PST crystal with the lamella plates oriented parallel to the compression axis. Six orientation variants of the gamma lamellae were present in similar proportions, but the most frequently observed gamma/gamma interface was of the true twin-type in the as-grown PST crystal. After creep deformation, the lamellae coarsened by the elimination of the gamma/gamma interfaces. The fraction of 120degrees rotational and pseudo-twin interfaces decreased, while that of true twin interfaces increased. The twin-related gamma/gamma interfaces migrated by ledge formation and its movement, and the interfaces disappeared by edge migration. The 120degrees rotational interfaces bulged and migrated substantially, and formed equiaxed grains. The alpha(2)/gamma interface was more stable than the gamma/gamma interface during creep deformation. Pseudo-twin and 120degrees rotational fault interfaces were less thermally stable than the true twin interface. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.