EFFECT OF LAMELLAR STRUCTURE ON FRACTURE-BEHAVIOR OF TIAL POLYSYNTHETICALLY TWINNED CRYSTALS

The fracture behaviors of Ti-49.1at.%Al and Ti-50.8at.%Al polysyntheti cally twinned crystals with fine and coarse lamellae, respectively, ha ve been investigated, focusing on the effect of the lamellar structure and loading axis. Type A and B specimens, in which the notch directio ns were parallel and perpendicular to lamellar planes, respectively, w ere prepared and compact tension tests were performed at room temperat ure. The fracture behavior exhibited strong anisotropy, depending on t he crack paths in the lamellae. For type A specimens, the crack propag ated very easily parallel to the lamellae, exhibiting low K-Q values, and a cleavage-like fracture on the (0001) plane in the alpha(2) phase was observed. In type B specimens, the crack propagated across the la mellar boundaries, exhibiting high K-Q values, and the boundaries acte d as an effective barrier to further crack propagation. Fine lamellae were beneficial in improving the fracture toughness.