Plastic behavior of TiAl PST crystals under cyclic loading conditions

Cyclic deformation and fatigue properties of TiAl polysynthetically twinned (PST) crystals have been investigated focusing on the effect of lamellar structure and plastic anisotropy on cyclic hardening, fatigue life and deformation substructure. Cyclic tension/compression loading was applied at room temperature at the total strain-controlled amplitude. Strong anisotropy in cyclic deformation was observed depending on the angle (φ) between the loading axis and the lamellar planes, and the deformation substructure in γ domain; the cyclic hardening became remarkable at φ = 0 degree, while at φ = 45 degree weak cyclic hardening was observed even at the point of the specimen failure. Fine lamellae were effective in improving the fatigue life. The domains were classified into two groups from the view point of the deformation substructure; they were T(twin)-type and V(vein)-type in which deformation twins and ordinary dislocations were dominantly operative, respectively. Highly dense and tangled ordinary dislocations in V-type domains were responsible for the strong cyclic hardening. Formation of twins was susceptible to the micro-crack initiation resulting in the shortage of fatigue life