Softening by spinodal decomposition in Au–Cu–Ni–Pd–Pt high-entropy alloys

At high temperatures, homogeneous solid solutions are formed in AuCuNiPdPt and AuNiPdPt alloys while annealing below critical temperatures causes decomposition into two chemically different solid solutions [1,2]. This particular circumstance is used to generate distinct variations in composition and to investigate their effect on the mechanical properties of AuCuNiPdPt and AuNiPdPt alloys. Various annealing treatments in terms of temperature and time lead to different microstructures allowing to evaluate the effect of the chemical compositions and their size on the mechanical properties. In any case, softening of the alloys is obtained. Moreover, the hardness is found to decrease with increasing amplitude of the concentration modulation and increasing size of the decomposed solid solutions. The results indicate that the effect of solid solutions on strength is not only dependent on solute-dislocation interactions but also affected by specific solute-solute interactions.