DEFORMATION AND FRACTURE UNDER COMPRESSIVE LOADING IN LAMELLAR TIAL MICROSTRUCTURES

A physically based micromechanical model is applied to study finite co mpressive deformation behaviour and the development of failure modes i n polycrystalline fully lamellar and nearly lamellar microstructures. Orientation-dependent yielding of lamellar TiAl single crystals is spe cifically modelled. Finite-element computations show that deformation is inherently non-uniform in the lamellar microstructure, in accordanc e 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 buc kling is found to be increasingly likely to occur at larger aggregate strains (i.e. strains larger than 5-10%). Internal buckling is found i n lamellar TiAl crystals whose lamellae are initially nearly parallel to the compressive loading. A weak basal texture, normal to the compre ssion axis, is developed at only 20% aggregate strain. Subtle variatio ns in microstructural constituents in lamellar and nearly lamellar TiA l are found to have significant influences on the flow and fracture be haviour.