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ABSTRACT
A precipitation hardening high-entropy alloy (HEA) (FeCoNi)86Al7Ti7 was fabricated by selective laser melting (SLM) and ageing treated under different temperatures and time conditions. Yield strength of the aged HEA increases substantially from 710 to 934 and then to 1203 MPa. Theoretical analyses reveal that the coherent L12 precipitate contributes most of the improved strength for the aged HEAs, whereas recovery during ageing causes the decrease of dislocation density thus exerts a softening effect. In addition, it is found that ductility decreases with increasing volume fraction of the incoherent L21 precipitates. Based on a void growth model, the trend is qualitatively explained. Moreover, a new fracture mode, intercellular fracture, is proposed to account for the strong dependence of fracture dimple size on the dislocation cells, also directly validated by delicate microstructural examination. The findings provide an effective strengthening method and propose a unique fracture mechanism for the additively manufactured HEA.
Acknowledgements
The authors sincerely thank Prof. Zhaoping Lu from the University of Science and Technology Beijing for his help in the discussion about the features of high entropy alloy, and the authors sincerely thank Prof. Jian Lu from the City University of Hong Kong for his help in the discussion about the additive manufacturing results.
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No potential conflict of interest was reported by the author(s).
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Notes on contributors
Yaowen Wu
Yaowen Wu is a graduate student in Additive Manufacturing Institute at Shenzhen University. His research focuses on developing processing-microstructure-properties relationships for high entropy alloys using selective laser melting technology.
Xinyi Zhao
Xinyi Zhao is a graduate student in Additive Manufacturing Institute at Shenzhen University. Her research focuses on establishing the multi-scale structure strengthening and toughening mechanism of SLMed high entropy alloy to jointly improve the strength and plasticity.
Qiang Chen
Qiang Chen is a graduate student in Additive Manufacturing lnstitute at Shenzhen University. His research focuses on application of SLM fabricated Fe-based nanocrystalline/amorphous alloy composite materials in catalytic degradation of organic pollutants.
Can Yang
Can Yang is an associate professor in Sino-German College of Intelligent Manufacturing, Shenzhen Technology University. His research interests cover additive manufacturing and precision manufacturing. He has 16-year research experience in material/product rheology, morphology, and performance regulation.
Mingguang Jiang
Mingguang Jiang is an associate research fellow in Additive Manufacturing Institute at Shenzhen University. His research focuses on the design and additive manufacturing of high performance metallic materials.
Changyong Liu
Changyong Liu is an associate professor in Additive Manufacturing Institute at Shenzhen University. His research interests include metal additive manufacturing and 3D printing of energy storage devices.
Zhe Jia
Zhe Jia is currently a Professor at School of Materials Science and Engineering, Southeast University and an ARC DECRA Fellow. Zhe's major research interest is on metastable metal and alloys, including amorphous alloys and high-entropy alloys. He has demonstrated and internationally recognized expertise in the design and processing of various compositionally complex alloys for wastewater treatment and water electrolysis by physical metallurgical techniques.
Zhangwei Chen
Zhangwei Chen is a professor and the director of Additive Manufacturing Institute at Shenzhen University. He works on the fields of preparation and manufacturing of high-performance materials and components, involving materials processing, additive manufacturing and characterizations etc.
Tao Yang
Tao Yang is an assistant professor of Materials Science and Engineering at the City University of Hong Kong. He also serves as the core member in the 3D-APT Unit of Hong Kong. His research is mainly focused on innovative design, fabrication, and microstructural control of advanced structural materials, including the intermetallic compounds, high-entropy alloys, superalloys, steels, and titanium alloys.
Zhiyuan Liu
Zhiyuan Liu is an associate professor in Additive Manufacturing Institute at Shenzhen University. His research interests include additive manufacturing of high entropy alloys, steels and bulk metallic glasses. And he is dedicated to revealing the principles of microstructural evolution during additive manufacturing and deformation mechanisms of the additively manufactured metals.