Abstract
The microstructural evolution of a metastable face centered cubic (FCC) Fe40Co20Cr20Mn10Ni10 high-entropy alloy (HEA) under both tension and compression is systemically investigated. The results show much higher level of martensite phase transformation from FCC structure to hexagonal closed packed (HCP) structure under compression than tension, indicating a distinct tension-compression asymmetry. The compressive tests underwent higher true stresses, which further provided stronger driving forces to trigger the phase transformation than those in tensile tests. Except for the martensite phase transformation, dislocation planar slip prevails in both tension and compression, along with the occasional formation of mechanical twins. Dislocation slip dominates the whole tensile deformation, while both dislocation motions and martensite phase transformation play critical roles in the compressive deformation. The martensite phase transformation is preferred to nucleate at grain or subgrain boundaries due to a medium stacking fault energy (SFE) of ∼20 mJ m−2. The formation of HCP phase via partial dislocation emission from low angle grain boundaries offers additional pathways for martensite phase transformation. Our study thus remarkably benefits the understanding of the de formation mechanisms of metastable HEAs.
摘要
本文系统研究了具有面心立方结构的亚稳态Fe40Co20Cr20-Mn10Ni10高熵合金在拉伸和压缩变形下的微观结构演变. 结果表明, 从FCC到HCP的马氏体相变在压缩条件下比在拉伸条件下要高得多, 具有明显的拉伸-压缩不对称性. 与拉伸试验相比, 压缩试验的真应力更大, 为马氏体相变的开启提供了更大的驱动力. 除马氏体相变外, 位错的平面滑移以及少量的变形孪晶在拉伸和压缩过程中均有发现. 位错滑移在整个拉伸变形过程中起主导作用, 而在压缩变形中位错运动和马氏体相变都起到了关键作用. 由于该高熵合金具有中等的层错能(20 mJ m−2), 因此马氏体相变更倾向于在晶界或亚晶界等高能区域处成核. 我们发现了六方马氏体相可以通过从小角晶界发射不全位错来形成, 这为马氏体相变提供了新的路径. 本研究对于理解亚稳态高熵合金的变形机制具有重要的意义.
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (51971247), and the open Foundation of State Key Laboratory of Powder Metallurgy at Central South University, Changsha, China.
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Author contributions Wang Z and Song M designed the project. An X prepared the materials, conducted the mechanical testing, and performed the TEM. Wang Z performed the EBSD and ECCI. An X, Wang Z, Ni S, and Song M analyzed the microstructural evolution. An X, Wang Z, and Song M wrote the manuscript. All authors contributed to the discussion and commented on the manuscript.
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Xinglong An is currently a PhD candidate with Prof. Song Ni and Prof. Min Song at Powder Metallurgy Research Institute, Central South University, China. His current research focuses on the microstructure characterization of metallic materials.
Zhangwei Wang is an Alexander von Humboldt fellow at the Max-Planck-Institut für Eisenforschung in Düsseldorf, Germany. He received his PhD degree in engineering from Dartmouth College, USA in 2017. His research primarily focuses on the development of advanced high-entropy alloys and lightweight steels.
Min Song is a professor and Vise Dean of Powder Metallurgy Research Institute at Central South University. He serves as Associate Editor of “Materials Characterization”. He received his PhD degree in 2005 at Dartmouth College, USA. His current research interests involve the deformation mechanisms of metallic materials, including: metals and alloys, bulk nanocrystalline materials, HEAs and metal matrix composites.
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An, X., Wang, Z., Ni, S. et al. The tension-compression asymmetry of martensite phase transformation in a metastable Fe40Co20Cr20Mn10Ni10 high-entropy alloy. Sci. China Mater. 63, 1797–1807 (2020). https://doi.org/10.1007/s40843-020-1319-3
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DOI: https://doi.org/10.1007/s40843-020-1319-3