Source: Additive Manufacturing Technology (3D Printing) Branch of Chinese Mechanical Engineering Society

Contributors: Cai Jianglong, Zhang Hang

Contributed by: State Key Laboratory of Mechanical Manufacturing Systems Engineering, Xi'an Jiaotong University

In 2004, Professor Ye Junwei, a Taiwanese scholar, broke away from the traditional alloy research and development ideas and proposed a new design concept of "multi-principal" alloys. "Multi-principal" alloys are usually composed of four or more metal elements in solid solution with an atomic percentage of 5% to 35%, so they are also called high-entropy alloys. High-entropy alloys have the following excellent properties: ultra-high hardness, high strength and high ductility, outstanding thermal stability, good wear resistance, corrosion resistance, good oxidation resistance, etc. Refractory High Entropy Alloys (RHEAs) are high-entropy alloys composed of high-melting point elements such as W, Ta, Nb, Mo, Hf, Re, etc. They are characterized by high strength and high density. Compared with conventional high-entropy alloys, it can maintain high strength at high temperatures and has good thermal stability. Therefore, the research on RHEAs is of great significance to the development of the aerospace field.

However, the advantages of RHEAs such as high melting point, high strength and high hardness also make it difficult or even impossible to form complex structural parts using traditional metallurgy, casting, machining and other technologies. Laser cladding deposition (LCD) technology is a rapidly developing laser additive manufacturing technology that can achieve a high degree of freedom in the preparation of RHEAs. The brittleness of the material itself and the high temperature gradient forming method of LCD make RHEAs have extremely poor room temperature ductility. Therefore, improving the ductility of RHEAs is the key to solving the problem of their inability to be put into the application market. Shuyuan Gou and others from Zhejiang University and Hunan University prepared TiZrHfNbx(x= 0.6, 0.8, 1.0) RHEAs using LCD. Increasing the Nb content can stabilize the BCC phase and inhibit the formation of the ω phase. This stage engineering strategy transforms mechanical properties from brittle to ductile fracture. The results show that the room temperature tensile yield strength of the TiZrHfNb alloy prepared by LCD is 1034 MPa and the ductility is 18.5%. Solid solution strengthening helps to increase the tensile yield strength, and local chemical composition fluctuations promote dislocation interactions and produce greater ductility. This research solves the problem of poor ductility of RHEAs prepared by LCD.

The use of LCD forming ductile RHEAs technology has outstanding advantages in the manufacturing of high-temperature resistant core components in nuclear engineering, aerospace, weapons and equipment and other fields, bringing disruptive innovative ideas to the manufacturing of these parts. Basic research on the materials and processes of this technology is of great scientific significance and engineering value, and provides solid guarantee and technical support for my country's high-end equipment manufacturing.

References:
Shuyuan Gou, Mingyu Gao, Yunzhu Shi, Shunchao Li, Youtong Fang, Xinhuan Chen, Huaican Chen, Wen Yin, Jiabin Liu, Zhifeng Lei, Hongtao Wang, Additive manufacturing of ductile refractory high-entropy alloys via phase engineering, Acta Materialia, Volume 248, 2023, 118781,ISSN 1359-6454,https://doi.org/10.1016/j.actamat.2023.118781.