Effects of Ti-to-Al ratios on the phases, microstructures, mechanical properties, and corrosion resistance of Al2-xCoCrFeNiTix high-entropy alloys

By Zhao, Yong; Wang, Mingliang; Cui, Hongzhi; Zhao, Yuqiao; Song, Xiaojie; Zeng, Yong; Gao, Xiaohua; Lu, Feng; Wang, Canming; Song, Qiang
Published in Journal of Alloys and Compounds 2019

Abstract

The Al2-xCoCrFeNiTix (x = 0, 0.2, 0.5, 0.8, 1.0, and 1.2) high-entropy alloys (HEAs) were prepared via vacuum arc melting. With the increase of the molar ratios of Ti-to-Al, the phases, microstructures, mechanical properties, and corrosion resistance of the HEAs were changed. The microstructures were transformed from BCC1+B2, and BCC2+BCC1+B2, to BCC2+Laves + BCC1 phases. The addition of Ti, on the one hand promoted the formation of another BCC phase and Laves phase, and on the other hand refined the microstructure of the as-cast alloys. Good comprehensive mechanical properties with the highest compressive fracture strength of 1919 MPa and fracture strains of 11.85% were obtained in the Al1.5CoCrFeNiTi0.5 alloy. With further increase in the ratio of Ti, the fracture strength and strains of the HEAs decreased because of the increase in the fraction and the size of the brittle Laves phase. Furthermore, compared with the Ti-free Al2CoCrFeNi alloy, all Ti-containing Al2-xCoCrFeNiTix alloys exhibited higher pitting corrosion resistance with a wide passive window. The existence of noble and unoxidized metal atoms in the passive film, particularly Ti, enhanced the alloy's resistance to pitting corrosion. Our report provides an effective method for the design of high Al-content HEAs to balance the strength-ductility trade-off and improve the pitting corrosion resistance synergistically.

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