A ductility-strength metric for chemically complex alloys

Local lattice distortions (LLD) – relative to average (x-ray) lattice positions – are expected in multiprincipal element alloys (MPEAs) due to the varying complex chemical environments. We suggest a dimensionless metric to characterize ductility in MPEAs using LLD. With its innate quantum-mechanical origins, ductility is clearly affected by LLD arising from increased atomic charge transfer due to electronegativity differences in each local environment (often designated by valence electron count (VEC)). To test this metric, we chose body-centered cubic (bcc) refractory alloys that exhibit a range of ductilitybrittleness. The metric was established by combining the weighted-average VEC and intrinsic parameters related to distortion from the average lattice. The electronic-structure results were calculated using density-functional theory (DFT) methods. The quantitative rank ordering of ductile-tobrittle MPEAs shows good agreement with recent mean-field estimates and experiments. Our results permit a quick ductility assessment to guide the design of more ductile high-temperature MPEAs, and potentially accelerated further if combined with machine-learning.