Abstract
Designing high entropy alloys (HEAs) with high strength and excellent ductility has attracted extensive scientific interest. In the present work, the CALPHAD (calculation of phase diagrams) method was applied to guide the design of an (FeCoNi)92Al2.5Ti5.5 HEA strengthened by precipitation hardening. The grain size as well as the size and volume fraction of the precipitates was tailored via a thermomechanical process to optimize the mechanical properties. The uniformly dispersed nano-precipitates are Ni3(Al,Ti)-type precipitates with an L12 ordered structure presenting a fully coherent interface with the face-centered cubic (FCC) matrix. The yield strength of the alloy increases from 338.3 to 1355.9 MPa and the ultimate tensile strength increases from 759.3 to 1488.1 MPa, while the elongation maintains a reasonable value of 8.1%. The striking enhancement of strength is mainly caused by the precipitate’s hardening mechanism, which is evaluated quantitatively by various analytical models. The deformation-induced microbands and the coherent precipitates sheared by dislocations are the deformation and strengthening mechanisms contributing to the superior combination of ductility and strength in the present HEA. This investigation demonstrates that the CALPHAD method is beneficial to the design and optimization of HEAs.
摘要
近年来, 设计具有高强度和优异延展性的高熵合金(HEAs) 引 起了人们的广泛兴趣. 在本文中, 我们采用 CALPHAD 方法来设计 沉淀强化型 (FeCoNi)92Al2.5Ti5.5 高熵合金.通过热机械处理过程来 调控合金晶粒尺寸、 析出相大小及体积分数, 性能. 在一定温度时效后, 具有, L12有序结构的Ni3(Al, Ti) 型第二相 在面心立方 (FCC) 基体中均匀析出, 并与FCC基体共格. 通过热机 械处理过程, 合金的屈服强度从 338.3 M Pa 增加到1355.9 M Pa, 抗拉 强度从 759.9 M Pa 增加到 1488.1 M Pa, 而伸长率仍然保持在 8.1%. 基 于分析模型定量评估屈服强度的增加, 结果表明屈服强度的显着 增加主要是由沉淀强化机制引起的. 变形引起的微观条带和位错 切过析出相是该合金的变形机制和强化机制, 有助于该合金同时 具有优异的延展性和高强度. 本研究表明, CALPHAD 方法可以为 高熵合金的设计和优化提供借鉴.
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Acknowledgements
This work was supported by the Fundamental Research Funds for the Central Universities of Central South University (2019zzts052) and the National Natural Science Foundation of China (51828102).
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Song M designed the project. Guo L and Gong X produced the materials and performed the mechanical testing. Guo L, Gu J, and Ni S conducted the microstructural characterization. Guo L, Gu J and Song M wrote the manuscript. All authors contributed to the discussion of the results and commented on the manuscript.
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The authors declare no conflict of interest.
Lin Guo is currently a PhD candidate at Powder Metallurgy Research Institute, Central South University, China. His current research focuses on HEAs designing and microstructural evolution.
Ji Gu is a lecturer of Powder Metallurgy Research Institute, Central South University, China. He received his PhD degree in material science and engineering in 2019 under the supervision of Prof. Min Song. His current research focuses on exploring the mechanical behaviour, deformation mechanism and structure-property relationship of HEAs and gradient structure materials.
Min Song is a Professor and Vice 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 deformation mechanisms of metallic materials, including: metals and alloys, bulk nanocrystalline materials, metallic glasses, HEAs and metal matrix composites.
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Guo, L., Gu, J., Gong, X. et al. CALPHAD aided design of high entropy alloy to achieve high strength via precipitate strengthening. Sci. China Mater. 63, 288–299 (2020). https://doi.org/10.1007/s40843-019-1170-7
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DOI: https://doi.org/10.1007/s40843-019-1170-7