Size dependent plasticity and damage response in multiphase body centered cubic high entropy alloys

The paper concentrates on the prediction of damage behavior in BCC HEAs and its subsequent dependence on intrinsic length scales. Size dependent plastic response is investigated using correlative nanomechanical testing, high resolution microscopy and phase analysis. Hot forged multiphase Al0.7CoCrFeNi HEA, comprising both face centered cubic (FCC) and body centered cubic (BCC) structured phases were used. Phase characterization inside the BCC grains indicated spinodal decomposition leading to a periodic arrangement of ordered B2 and disordered A2 phases. Room temperature nanoindentation response in the BCC grain revealed appearance of repeated strain bursts occurring in a random and stochastic manner. The observed plastic behavior was correlated to dislocation hardening mechanisms arising from a combination of the spinodally modulated microstructure and order hardening effects. Interestingly, in contrast to the commonly observed FCC to BCC transformations, certain indents revealed a structural transition from BCC to FCC. The stress induced microstructural evolution is discussed in terms of inherent compositional gradients and relevant defect-interphase interactions.