Cyclic deformation behavior of an equiatomic CrFeNi multi-principal element alloy

Abstract

For multi-principal element alloys (MPEAs) potential engineering applications, understanding their low-cycle fatigue (LCF) behavior is of decisive importance. Recently, an equiatomic face-centered cubic (FCC) CrFeNi has been shown to offer an excellent combination of monotonic properties. In the present study, we report on its LCF behavior at room temperature. Fully reversed strain-controlled fatigue tests were conducted in air under three different strain amplitudes (±0.3 %, ± 0.5 % and ± 0.7 %). The measured cyclic stress response reveals a rapid increase (i.e., cyclic hardening) followed by a relatively gradual decrease of peak stresses (i.e., cyclic softening) until failure. Electron microscopy investigations on post-fatigue samples revealed strain amplitude dependent dislocations slip-mode and resulting substructures evolution. These observations are linked to the observed cyclic stress response and lifetime. Furthermore, the origin of CrFeNi’s cyclic stress response is analyzed by partitioning hysteresis loops. Lastly, a comparison with similar grain-sized (60–67 µm) equiatomic CoCrFeMnNi, and 316L alloys pinpoints the peculiarities of CrFeNi LCF response, which is discussed in terms of the difference in their solid solution strengthening, grain boundary strengthening and stacking fault energy.