Hard-oriented polysynthetically twinned crystals with lamellar plates oriented parallel to the compression axis were deformed at 1150K using applied stresses of 158 to 316MPa. Microstructural changes were determined quantitatively during creep deformation. In as-grown crystals, the proportions of α2/γ, true twin, pseudo-twin and 120º rotational fault interfaces were 12, 59, 12 and 17%, respectively. Following creep deformation, lamellar coarsening via dissolution of α2 lamellae and migration of γ/γ interfaces was observed. An acceleration of the creep rate, after the minimum strain-rate in the creep curve, was attributed to lamellar coarsening and destruction of the lamellar structure during creep deformation. Some 32% of the α2/γ interfaces, 51% of the true twin interfaces, 74% of the pseudo-twin interfaces and 80% of the 120º rotational faults disappeared after 4% of creep strain at 1150K. The α2/γ interface was more stable than the γ/γ interfaces during creep deformation. The pseudo-twin interface and the 120º rotational fault were less thermally stable than the true-twin interface or γ/γ interfaces.

Microstructure Stability during Creep Deformation of Hard-Oriented Polysynthetically Twinned Crystal of TiAl Alloy. H.Y.Kim, K.Maruyama: Metallurgical and Materials Transactions A, 2003, 34[10], 2191-8