バイモーダル構造を有するハイエントロピー合金CrMnFeCoNiの創製とその疲労き裂伝ぱ特性

抄録

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 and powder metallurgy. The HEA with a bimodal structure was fabricated by sintering nitrided HEA powders. Stress intensity factor, K, decreasing tests were conducted under the force ratios, R, from 0.1 and 0.5 in air at room temperature to investigate the near-threshold fatigue crack propagation in CrMnFeCoNi alloys with a bimodal structure. Threshold stress intensity range, ΔK_th, of nitrided HEAs compact tested at R = 0.1 was lower than that of the un-nitrided one, whereas ΔK_th of nitrided HEAs compact tested at R = 0.5 showed almost the same as the un-nitrided one and effective threshold stress intensity range, ΔK_eff,th, was higher than that of the un-nitrided one. After testing, crack profiles were observed by scanning electron microscopy, and microstructures around crack profiles were analyzed using electron backscatter diffraction and electron prove micro analysis to discuss the mechanism of fatigue crack propagation. In some areas, fatigue crack paths in nitrided HEAs compacts were influenced by a bimodal structure.