Microscale deformation controlled by compositional fluctuations in equiatomic Nb-Mo-Ta-W alloys

Local fluctuations in the chemical composition of high-entropy alloys (HEA) are known to have a significant influence on their mechanical performance. In this work, we conclusively establish a direct link between the strength of micron-sized specimens and deviations from equiatomic stoichiometry in body-centered-cubic (bcc) refractory Nb-Mo-Ta-W HEA. We perform a detailed electron dispersive spectroscopy (EDS) line profile analysis of the compressed micropillars after in-situ scanning electron microscopy microcompression tests at room -temperature and strain rates between 10-4 and 10-1 s-1. We find that compositional fluctuations near the micropillar tip is the best quantitative predictor of yield strength over strain rate and grain orientation. In micropillars tip rich in W, we measure a yield strength of 1500 MPa, while for those with a Ta and Nb-rich oscillations, the yield strength is 1000 and 700 MPa, respectively. Finally, our high-resolution TEM analysis reveals the presence of numerous edge dislocations, suggesting that deformation is controlled by nucleation due to the absence of sufficient internal sources.

Automated summary

In this study, the direct link between the strength of micron-sized specimens of high-entropy alloys and deviations from equiatomic stoichiometry was established. The compositional fluctuations near the micropillar tip were found to be the best quantitative predictor of yield strength.