Stability of lamellar microstructure of hard orientated PST crystal of TiAl alloy Original Research Article

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 α2/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.