Ryo Ueta

A Dislocation-Based Crystal Plasticity Simulation on Kink Band Formation and Evolution in Polycrystalline Mg Alloy with LPSO Phase

A three-dimensional compression analysis is performed by finite element method using a dislocation-based crystal plasticity model to clarify the formation mechanism of kink band in a polycrystalline Mg alloy with a long-period stacking ordered structure (LPSO) phase. The crystalline structure of LPSO phase is regarded as a HCP for simplicity, however, any deformation twinning is not taken into account. In addition, the activities of non-basal systems are considerably limited in the LPSO phase setting the values of their critical resolved shear stresses to large ones. We analyze a simple polycrystalline specimen composed of two α-Mg matrix phases and a LPSO phase both having a rectangular shape and twist grain boundaries are introduced into the interface. The obtained result shows that the kink band formation in the alloy is accomplished by the basal slips with different variants and the non-basal slips are activated on the grain boundary to maintain the continuity of deformation.

Multiscale simulation of dynamic recrystallization for α-Mg phase in Mg/LPSO alloys based on multi-phase-field and dislocation-based crystal plasticity model

Magnesium alloy with Long-Period Stacking Ordered Structure (LPSO) and α-Mg (ordinary HCP structure) phase is expected for a new structural material due to its excellent mechanical properties. Its materials strengthening arises from the kink band formation in LPSO phase and the grain refinement of α-Mg phase in the vicinity of LPSO phase because of recrystallization. In the present study, a multiscale and multiphysics computation for the dynamic recrystallization in α-Mg phase is carried out by coupling the dislocation-based crystal plasticity model for HCP crystals proposed previously by the authors with the multi-phase field model through dislocation density. In the present model, not only the environmental temperature-dependences of nucleation and nucleus growth but also a pinning effect of boundary migration of recrystallized grain boundary owing to existence and influence of additive elements are newly taken into account. Furthermore, grain size behaviors of recrystallized nuclei are investigated for various volume fractions of additive element and ratios of grain boundary segregation.