Enhancing creep resistance of aged Fe–Cr–Ni medium-entropy alloy via nano-sized Cu-rich and NbC precipitates investigated by nanoindentation

Abstract

Materials with high creep resistance are required for next-generation fossil and nuclear power plants. In this study, the effect of aging on the creep resistance of a Fe–Cr–Ni medium-entropy alloy (MEA) was investigated via a nanoindentation test. The precipitate evolution in the aged MEA was analyzed by the electron channeling contrast imaging (ECCI) technique. The volume fraction and size of the precipitates in different aging states were characterized and analyzed quantitatively. The strain rate sensitivity and activation volume were estimated to analyze the creep properties and mechanism. The precipitates of the MEA evolved with aging time, consisting of Z phases, M23C6 carbides, Cu-rich, and NbC particles. With the extension of aging time, the strain rate sensitivity first increased, then decreased, and finally tended to be stable. The creep behavior of the Fe–Cr–Ni MEA was controlled by the interaction between dislocation and precipitates. The Fe–Cr–Ni MEA has excellent creep resistance after long-term aging, benefiting from the nano-sized Cu-rich and NbC precipitates that significantly enlarged the dislocation pinning effect. The understandings obtained from this work could benefit the development and optimization of the creep-resistant MEAs.

Keywords

• Medium-entropy alloy
• Creep
• Precipitate
• Nanoindentation
• Aging