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

Abstract 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 γ lamellae were present in similar proportions, but the most frequently observed γ / γ interface was of the true twin-type in the as-grown PST crystal. After creep deformation, the lamellae coarsened by the elimination of the γ / γ interfaces. The fraction of 120 ° rotational and pseudo-twin interfaces decreased, while that of true twin interfaces increased. The twin-related γ / γ interfaces migrated by ledge formation and its movement, and the interfaces disappeared by edge migration. The 120° rotational interfaces bulged and migrated substantially, and formed equiaxed grains. The α 2 / γ interface was more stable than the γ / γ interface during creep deformation. Pseudo-twin and 120 ° rotational fault interfaces were less thermally stable than the true twin interface.