Coupled crystal plasticity finite element-phase field model with kinetics-controlled twinning mechanism for hexagonal metals

Abstract

Hexagonal metals plastically deform through evolution of dislocations and twins. Deformation twinning is unidirectional and results in twin domain associated with crystal reorientation. Growth of a twin domain is accomplished through nucleation and motion of twinning dislocations/ disconnections (TDs) at atomic scale, and described by migration of twin boundaries (TBs) at micro/macro-scales. Corresponding to kinetics-controlled migration mechanisms of twin boundaries, a coupled crystal plasticity finite element-phase field (CPFE-PF) model was developed through implementing microscale twinning model with anisotropic mobilities of twin boundaries. Crystal plasticity finite element model (CPFEM) is used to solve elastic fields and plastic deformation (carried by both dislocation slip and twinning). Phase field (PF) method is adopted to spatially distinguish twin domains from matrix and track the migration of TBs. Migration of TBs is controlled by both anisotropic mobility coefficients that are correlated to experimental measured twinning strain rate, and the twin driving force contributed by strain energy that is calculated from CPFEM, and change of interface energy including chemical energy and gradient energy that is calculated using finite volume method. It is worth mentioning that experimental measured interface energies of TBs and a critical gradient criterion are adopted in PF model to confine the width of TBs. Our CPFE-PF model exhibits the capability of predicting twin growth with experimental observed twin morphologies, and can be further developed to study twinning related microstructural evolution and mechanical behavior for hexagonal metals.