Origins of strength and plasticity in the precious metal based high-entropy alloy AuCuNiPdPt

The precious metal based High-Entropy Alloy (HEA) AuCuNiPdPt crystallises in a face-centred cubic structure and is single phase without chemical ordering after homogenisation. However, a decomposition is observed after annealing at intermediate temperatures. This HEA shows extended malleability during cold work up to a logarithmic deformation degree of phi = 2.42. The yield strength ranges from 820 MPa in the recrystallised state to 1170 MPa when strain hardened by cold working with a logarithmic deformation degree of phi > 0.6. This work hardening behaviour is traced back to a steep increase in dislocation density as well as in deformation twinning occurring at low strain. The microstructure and the mechanical properties of AuCuNiPdPt are assessed in detail by various methods. EBSD and TEM analyses reveal mechanical twinning as an important deformation mechanism. The high strength in the recrystallised state is evaluated and found to originate predominantly upon solid solution strengthening. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.