Hierarchical multiscale crystal plasticity framework for plasticity and strain hardening of multi-principal element alloys

Abstract

The multi-principal element alloys (MPEAs) exhibit the unprecedented combinations of the excellent mechanical properties, especially high strength and good ductility. However, the accurate and reasonable models for describing the mechanical behavior of MPEAs are still scarce due to their distinctive serious lattice distortion effects, which limit the performance prediction. Here, we develop a new general framework by combining the atomic simulation, discrete dislocation dynamics, and crystal plasticity finite element method, to study the strain-hardening behavior for MPEAs, which achieves the influence of the complex cross-scale factors, including the lattice distortion at the nanoscale and the dislocation hardening at the microscale, on the plastic deformation. Compared with the classic crystal plasticity finite element, the bottom-up hierarchical multiscale model could couple the underlying physical mechanisms from the nano-micron-meso scales and captures the inhomogeneous strain field induced by the serious lattice distortion, thus showing the high accuracy and ubiquitous availability for MPEAs. The result shows that the prediction of the strain-stress curve in the polycrystal MPEAs agrees well with the experimental result at the quasi-static tension, which verifies the accuracy of the proposed method. In addition to the dislocation evolution, the heterogeneous strain distribution combined with the significant change from the orientation of some grains could be an important reason for the enhanced strength at the micron scale. The present work not only gives an insight into the relationship between the multiscale microstructure and strain hardening considering the mechanistic linkages of the lattice distortion, dislocation behavior, and grain structure, but also provides a general approach to physically predict the mesoscopic mechanical response in MPEAs.