Solid solution strengthening in single-phase Au-Cu-Ni-Pd-Pt-based high-entropy alloys

The Au-Cu-Ni-Pd-Pt system is an ideal benchmark system to investigate the composition-dependent effect on solid solution strengthening in multi-element alloys, in particular high-entropy alloys. It allows studying the strength for deliberately adjusted compositional variations without any phase transformations taking place. In this study, alloy series are produced, in which one element is gradually replaced by another while these two elements are additionally alloyed to an equimolar three-element solid solution. The variations in concentration x are as follows: AuxNi25-x(CuPdPt)75 and NixPt25-x(AuCuPd)75 (x = 0, 5, 10, 15, 20, 25 at%). A non-linear trend of strength vs. concentration x is observed with maximum values close to the equimolar ratio of the two interchanged elements. The observed behavior cannot be explained by the commonly accepted model for solid solution strengthening of Varvenne and co-workers [1]. Possible reasons for the discrepancy between model and experiment are critically discussed.