Solid Solution Strengthening from Medium- to High-Entropy Alloys

A fundamental understanding of the strength of multi-component alloys relies on well-defined experiments accompanied by accurate modelling. Whilst much work has been done so far for equi-atomic alloys, little has been done to investigate the effect of solid solution strengthening for alloys with deliberately adjusted, non-equimolar composition that are varied in certain concentration steps, including particularly continous changes between equimolar subsets of alloy systems. This systematic approach is a key tool to verify or falsify current theories for solid solution strengthening for highly concentrated alloys. Series of alloys where a fifth element is alloyed to an equi-atomic four component alloy were prepared from Au, Cu, Ni, Pd and Pt, respectively. All investigated alloys form a single-phase solid solution, which is proven on a wide range of length scale by means of XRD, SEM and APT measurements. The mechanical properties of the series are compared to the predicted yield strengths calculated upon the model of Varvenne et al. [Varvenne et al. Acta Mater. 124 (2017) p600]. The present results highlight coincident and discrepant results between experiment and model.