Fatigue Crack Propagation in High-Entropy Alloy CrMnFeCoNi Fabricated by Mixed Sintering of Nitrided Powders

High entropy alloys (HEAs), which have five or more principal elements with an equiatomic composition, exhibit multiple excellent mechanical properties. Superior fatigue properties would be required to use HEAs as structural components in engineering fields. The purpose of this study is to develop HEAs having high crack propagation resistance via melamine reduction-nitridation process and powder metallurgy. The HEA compact was fabricated by mixed sintering of nitrided and un-nitrided CrMnFeCoNi powders to control the amount of nitrogen addition. Stress intensity factor, K, decreasing tests were conducted for CrMnFeCoNi alloys with nitrogen at force ratios, R, from 0.1 to 0.8 in air at room temperature. Threshold stress intensity range, ΔKth, of HEA compact with nitrogen was almost the same as the un-nitrided one at R = 0.1, whereas ΔKth of HEA compact with nitrogen was high in comparison to the un-nitrided one at R = 0.7. This was because the nitrogen addition increased the effective threshold stress intensity range, ΔKeff,th, of the HEA compact, but the magnitude of crack closure was reduced. The HEA compact with nitrogen shows excellent fatigue crack propagation properties, especially at high R conditions where crack closure does not occur.