An experimental and crystal plasticity simulation study on kink band-assisted grain fragmentation during high-pressure torsion of (CrFeNi)99Si1 medium-entropy alloy

The current research addresses the kink band-assisted grain fragmentation of (CrFeNi)99Si1 medium-entropy alloy during high-pressure torsion (HPT) using combinatorial experimental and crystal plasticity simulations approach. The HPT experiments were carried out at room temperature with a pressure of 6 GPa for 0.2, 0.5, 1, 2, and 5 turns to achieve different levels of shear strain followed by detailed microstructural characterization using electron backscatter diffraction, transmission electron microscopy, and nanoindentation. Microstructural characterization at different length scales shows the fragmentation of grains aided by the formation of kink bands due to the activation of {111} $$<10overline{1 }>$$ and {111} $$<11overline{2 }>$$ slip system followed by gradual conversion of low-angle grain boundaries to high-angle grain boundaries by continuous dynamic recrystallization (cDRX) observed in medium and low stacking fault energy FCC metals and alloys. This aforementioned mechanism occurs over a range of length scales, scaling down the grain size over three orders of magnitude from 40 ± 5 μm to 35 ± 3 nm. Crystal plasticity simulations using the fast Fourier transform solver were employed for full-field simulations to capture the process of kink band-assisted grain fragmentation using the open-source Dusseldorf advanced material simulation kit (DAMASK) software. Finally, constitutive strength equations were developed to quantitatively predict the evolution of strength as a function of HPT deformation to establish the processing-microstructure-mechanical property in (CrFeNi)99Si1 medium-entropy alloy.