Deformation and fracture under compressive loading in lamellar TiAl microstructures

A physically based micromechanical model is applied to study finite compressive deformation behaviour and the development of failure modes in polycrystalline fully lamellar and nearly lamellar microstructures. Orientation-dependent yielding of lamellar TiAl single crystals is specifically modelled. Finite-element computations show that deformation is inherently non-uniform in the lamellar microstructure, in accordance with results presented earlier by Kad, Dao and Asaro. Intergranular fracture initiation is found to be expected at small aggregate strains (i.e. strains less than 5%), while fracture initiated by internal buckling is found to be increasingly likely to occur at larger aggregate strains (i.e. strains larger than 5-10%). Internal buckling is found in lamellar TiAl crystals whose lamellae are initially nearly parallel to the compressive loading. A weak basal texture, normal to the compression axis, is developed at only 20% aggregate strain. Subtle variations in microstructural constituents in lamellar and nearly lamellar TiAl are found to have significant influences on the flow and fracture behaviour.