Finite element modelling of dual-phase polycrystalline Nickel-base alloys

A 3D finite element model was developed to simulate the influence of inclusions on the polycrystalline mechanical behavior of dual-phase Nickel-based alloys. A dislocation based strain hardening model, constructed in the so-called Kocks-Mecking framework, is used as the main strategy for the constitutive modeling of individual phases. To determine the influence of phase type, inclusion size, shape and distribution, on the inelastic stress-strain distribution, the digital microstructure code DREAM.3D was coupled to ABAQUS® code through a MatLab® program. Four dual-phase Representative Volume Elements (RVEs) of similar edge size but different inclusion size, morphology and distribution were tested to investigate the relation between micro and macro deformation and stress variables. The virtual specimens subjected to continuous monotonic strain loading conditions, were constrained with 3-D boundary conditions. A phenomenological approach is used to account for the effects of plastic strain gradients in hardening.The difference in crystallographic orientation, which evolves in the process of straining, and the incompatibility of deformation between neighboring grains were accounted for the evolution of geometrically necessary dislocation density, by the introduction of averaged Taylor factors, averaged Young´s modulus and single phase elastic limit. The effects of microstructural features upon the aggregate local response are clearly observed. Quantified results demonstrate a strong dependence of flow stress and plastic strain on phase type, inclusion size, shape and distribution. The results are in agreement with the expected output that the flow resistance is higher for structures composed of finer and homogeneously distributed inclusions.