WEB Effects of solutes on the microstructure and properties of UFG materials from dilute binary systems to high entropy alloysWednesday (01.01.2020) 00:00 - 00:30 Part of:
The influence of solutes in terms of stacking fault energy and solid solution hardening on the saturation grain size after severe plastic deformation was studied recently for binary Cu-Zn and Cu-Sn alloys, showing that the saturation grain size correlates with the solid solution strengthening contribution and not with the stacking fault energy. Whether this correlation still holds for high entropy alloys that are well beyond the scope of classical solid solution hardening theories remains an open question which is addressed in this contribution. A series of Nickel diluted compositions from pure Nickel to the chemically complex equiatomic CrMnFeCoNi Cantor alloy ((CrMnFeCo)xNi1-x) with x=0.8, 0.4 and 0.08 were subjected to high pressure torsion and investigated with regards to their microstructure and mechanical properties. The solid solution strengthening contribution was determined using the conventional Labusch model and the more recent Varvenne model that was specifically developed for chemically complex alloys. Similar to the binary Cu-alloys, a correlation between the solid solution strengthening contribution and the saturation grain size can be found, i.e. a higher Δτ causes a smaller saturation grain size. Nanoindentation strain rate jump tests show similar low strain rate sensitivities of the deformed states without any pronounced transient regimes, despite the substantially different saturation grain sizes that vary up to a factor of 3 between pure Ni and the equiatomic Cantor alloy. Furthermore, all compositions exhibit a history dependent softening, which indicates an unstable microstructure.