Liu Yang, Jiang Ping, Duan Guihua, Wang Jing, Zhou Lingling, Xie Jijia
State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China.
Materials (Basel). 2022 Sep 1;15(17):6081. doi: 10.3390/ma15176081.
The behavior and the mechanism of fatigue crack propagation in CrCoNi medium-entropy alloys (MEAs) with heterogeneous microstructures were investigated in this paper. After cold-rolling and recrystallization annealing at different temperatures and times, five sets of heterostructured specimens were acquired with different recrystallization levels. Then, the structure characterizations of these five sets of specimens were carried out by nanoindentation testing and electron back-scatter diffraction (EBSD) mapping. Finally, the fatigue crack propagation tests were conducted on single edge crack specimens of these different heterogeneous microstructures. The experimental results indicate that the crack propagation rates of specimens with partial recrystallization microstructures are higher than those with complete recrystallization microstructures, and the effect on fatigue crack thresholds of these specimens is the opposite. The fatigue cracks grow along the slip planes or twin boundaries in recrystallization grains (RGs), which induced crack deflections and the roughness-induced crack closure effect. For this reason, the area percentage of recrystallization and the grain size of RGs have a great effect on the value of the fatigue crack growth threshold.
本文研究了具有异质微观结构的CrCoNi中熵合金（MEA）中疲劳裂纹扩展的行为和机制。通过在不同温度和时间下进行冷轧和再结晶退火，获得了五组具有不同再结晶程度的异质结构试样。然后，通过纳米压痕测试和电子背散射衍射（EBSD）映射对这五组试样进行了结构表征。最后，对这些不同异质微观结构的单边裂纹试样进行了疲劳裂纹扩展试验。实验结果表明，具有部分再结晶微观结构的试样的裂纹扩展速率高于具有完全再结晶微观结构的试样，而对这些试样的疲劳裂纹阈值的影响则相反。疲劳裂纹沿再结晶晶粒（RG）中的滑移面或孪晶界扩展，这导致了裂纹偏转和粗糙度诱导的裂纹闭合效应。因此，再结晶的面积百分比和RG的晶粒尺寸对疲劳裂纹扩展阈值的值有很大影响。
