Microstructural influences on the micro-macro deformation of a two-phase Gamma TiAl alloy using a multiscale approach

Abstract

Room temperature deformation behaviour of niobium-containing two-phase TiAl alloy has been investigated numerically using a two-scale micromechanical finite element model. A polycrystal with duplex microstructure consisting of globular and lamellar grains is modeled with 3D unit cells that take into account specific volume fractions and orientations of the grains. The globular unit cell is described by representative volume elements of γ-phases whereas the lamellar unit cell is constructed with representative volume elements of α2 and γ-phases (matrix and twin γ-phases with their orientation relationships). The constitutive behaviour of the phases is described by a continuum mechanics based crystal plasticity model with a rate-dependent viscoplastic formulation. The unit cells (at micro-scale) are used as a material sub-model for the polycrystal (at macro-scale). Quantitative representations of microstructural details are obtained from the SEM analysis of a particular TNB alloy. The material parameters of the α2 and γ-phases are initially taken from the literature and modified to fit the behavior of the niobium-containing TiAl alloy, correlating the experimental tensile records at room temperature with the simulation results. The model provides an insight into the local variation of stresses and strains of the duplex microstructure consisting of globular grains and lamellar colonies. The role of dislocations and slip systems on the evolution of local plastic deformation will be discussed.