Guide
A new strategy based on infinite solid solution and pseudo-ternary model is proposed to reveal the mystery of three-phase eutectic high-entropy alloys (TEHEAs). The designed TEHEAs with more than 7 elements have face-centered cubic (FCC), ordered body-centered cubic (B2) and Laves phase structures, among which (CoCrFeNi)68(NiAl)18-Mo3.5Nb6Ta4.5 alloy exhibits excellent comprehensive mechanical properties, which provides a new way for the design of high-performance EHEAs.
The proposal of high-entropy alloys (HEAs) has opened up a new frontier in the field of metal materials and created a broad space for the exploration of the field of alloy material design. Eutectic alloys have good fluidity, which can effectively prevent casting defects and improve mechanical properties. Eutectic high-entropy alloys (EHEAs) combine the advantages of HEAs and traditional eutectic alloys with good castability and strength-plastic synergy, making them potential candidates for high-temperature applications.
At room temperature, as-cast FCC phase + B2 phase EHEAs have an excellent combination of breaking strength-plasticity. However, the characteristics of the enhanced B2 phase limit the room temperature yield strength of the FCC phase + B2 phase, while the high yield strength of structural applications can meet more stringent stiffness requirements, and the high-temperature mechanical properties of the B2 phase are not ideal. EHEAs characterized by the combination of FCC phase + Laves phase generally exhibit higher yield strength and excellent mechanical properties at high temperatures, thanks to strong Laves phase enhancement, however, they have poor plasticity at room temperature. Based on the cocktail effect of high-entropy alloys, the design of three-phase eutectic high-entropy alloys (THEAs) with FCC + B2 + Laves composite structure can make full use of the performance advantages of the above two EHEAs.
In the design of HEAs, the moderate addition of multiple elements will lead to the redistribution of the spatial structure in the material, affecting the evolution or formation of grain boundaries and intragranular and other defects, providing more possibilities for optimizing alloy properties. However, the design of multi-element/three-phase eutectic high-entropy alloys (TEHEAs) is still confusing.
近日，三峡大学叶喜葱教授课题组联合大连理工大学、哈尔滨工业大学的科研团队提出了一种将无限固溶法和伪三元法与热力学软件模拟相结合的新策略来设计TEHEAs。 研究结果以题为“A New Strategy for the Design of Triple-Phase Eutectic High-Entropy Alloys Based on Infinite Solid Solution and Pseudo-Ternary Method”发表于期刊《Nano Letters》。
The first author of this paper is Professor Ye Xineng of China Three Gorges University, and the corresponding authors are Professor Ye Xineng of China Three Gorges University, Professor Kang Huijun of Dalian University of Technology, and Dr. Li Zhe of Harbin Institute of Technology. This paper was supported by the Key Laboratory of Laser, Ion and Electron Beam Modified Materials of the Ministry of Education (KF2304) of Dalian University of Technology.
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In this method, the three components in the conventional ternary eutectic phase diagram were replaced by pseudo-ternary elements NiAl, CoCrFeNi and M, respectively, and four TEHEAs containing 7 or more elements were successfully designed. When the number of alloying elements is less than 8, the eutectic structure is fine, in the form of regular lamellae, surrounded by coarse eutectic. When the number of elements reaches 9, the eutectic structure morphology tends to be coarsened and irregular, which is due to various factors, such as atomic size and chemical affinity, as well as diffusion rates and preferences for various elements in the alloy.
Within the scope of research, second-phase strengthening is the main mechanism to improve the yield strength of alloys. Due to the addition of 9 elements, the diffusion rate of (CoCrFeNi)67(NiAl)20Mo3Nb4.5Ta4W1.5 alloy is different, which affects the migration and rearrangement of atoms, which may lead to the increase of grain size, thereby affecting the overall mechanical properties of the alloy.
In addition, the multi-element composition and complex structure of the alloy further complicate the diffusion behavior between the elements. Therefore, adding the right amount of additional alloying elements can help to optimize the structure of the alloy by controlling the diffusion process, thereby improving the performance. At the same time, the addition of more alloying elements can further exert the cocktail effect of high-entropy alloys to meet the more stringent requirements of high-temperature applications. The results verify the feasibility of using a new strategy combining the infinite solid solution method and the pseudo-ternary method to design FCC+Laves+B2 TEHEAs.
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