Deformation behavior and cracking of heat-treated Ti-46 mol%Al alloy with a coarsely spaced lamellar structure has been investigated by a discontinuous compression test and electron probe microanalysis.
Cracking of specimens with a coarsely spaced lamellar structure occurs at a compression plastic strain of 2.1% and a stress of 650 MPa. Crack initiation sites were clarified as \ding172 on a colony and a grain boundary of the lamellar structure, \ding173 within the α2 phase of the lamellar structure with the compression axis perpendicular to the lamellar planes, \ding174 on a near lamellar interface, and \ding175 within massively transformed α2 phase or on its interface. Fracture behavior of the specimens is explained as follows. A number of cracks mentioned above increased with increasing compression strain, and then the cracks propagate while growing and combining with each other, and making shear ligaments and deflections. The main crack propagates in a shear direction resulting in fracture.
Deformation behavior and dependence of angles between the compression axis and the lamellar planes were studied in polycrystals with a coarsely spaced lamellar structure on compression test. In the lamellae with the compression axis perpendicular to the lamellar planes, cracking within the α2 phase was observed without explicit deformation traces. On the other hand, in the lamellae with the compression axis parallel to the lamellar planes, a hard type of deformation across the lamellae occurred in the γ phase. However for the compression axis at intermediate angles, a hard type and an easy type of deformation traces were observed in the γ phase in addition to activation of a prism slip system in the α2 phase.
