Nanoindentation behavior of Al_0.3CoCrFeNi high entropy alloy: Experimental study and crystal plasticity finite element simulation

The effects of loading rate and grain orientation on the deformation behavior of the Al_0.3CoCrFeNi high entropy alloy (HEA) under nanoindentation loading were investigated experimentally and numerically, respectively. Experimental results demonstrated that the nanoindentation creep behavior of the alloy is highly sensitive to the loading rate: a higher loading rate results in smaller displacement during the loading stage and greater creep displacement during the holding stage. This is because, at lower loading rates, creep deformation has sufficient time to develop during the loading stage. X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) were conducted to obtain crystallographic information for input into the crystal plasticity finite element model (CPFEM). A representative volume element (RVE) finite element model of the alloy was reconstructed, and uniaxial tensile simulation was performed to validate the accuracy of the CPFEM and its parameters set. Based on the stress contour of tensile simulation result, 8 representative grain orientations were selected to investigate their influence on nanoindentation deformation using CPFEM. The results indicate that nanoindentation deformation in the HEA is strongly affected by grain orientation. Different grain orientations significantly affect the spatial distribution of shear strain, which in turn affects the morphology and distribution of the pile-up during nanoindentation. A combined analysis of the uniaxial tension and nanoindentation simulations reveals that grains with soft orientations are more prone to stress concentration during polycrystalline deformation and exhibit more pronounced pile-up in the single crystal nanoindentation. The grain exhibiting pronounced stress concentration under uniaxial tensile loading also demonstrates a distinct pile-up morphology and relatively large pile-up height in the nanoindentation simulations. In contrast, the grain located in a low-stress region during tensile loading consistently shows a smaller pile-up height. By incorporating CPFEM into the nanoindentation analysis of HEA, this study not only improves the resolution of micromechanical characterization but also provides a theoretical foundation for elucidating their intrinsic plasticity mechanisms and for designing cross‑scale strengthening strategies.