Tune Al/Ti to adjust FCC+L21 hetero-structured Ni-based high-entropy alloys for improved mechanical properties and wear resistance
Guijiang Diao, Yunqing Tang, Anqiang He, Mingyu Wu, Dong Zhang, D. Fraser, Jing Li, R.J. Chung, Dongyang Li
Abstract
Outstanding mechanical properties of Ni-based superalloy benefit from its coherent γ/γ’ structure via precipitation strengthening of γ matrix (FCC structure) by L1 2 Ni 3 Al-type γ’ phase. Back-stress strengthening is another effective strategy to further enhance the FCC+L1 2 structured Ni-based superalloy. In this work, we extend such approaches to high-entropy alloys (HEAs) by introducing different Al and Ti contents (5 at.% ∼18 at.%) into a Ni-based CrFe 2 Ni 4 alloy to form FCC+L2 1 heterostructured Al x CrFe 2 Ni 4 Ti y HEAs. Detailed microstructural analysis indicates that L1 2 Ni 3 (Al,Ti)-type nanoparticles form in a (Ni,Fe,Cr)-rich FCC matrix. The volume fraction of L2 1 AlNi 2 Ti-type phase can be varied by adjusting the Al/Ti ratio and concentrations of Al and Ti. Higher Al and Ti contents promote L2 1 phase formation and higher Al/Ti ratio (>1) prohibits the high Ti-containing compounds such as D0 24 η -Ni 3 Ti and C14 Laves Fe 2 Ti phases, which are hard but brittle. Corresponding Young's modulus , Poisson's ratio , hardness, and the bulk to shear modulus ratio (B/G) can be readily modified. Compressive tests demonstrate that Al 1.5 CrFe 2 Ni 4 Ti 1.0 alloy with half FCC and half L2 1 phases possesses the optimal strength-ductility combination (with compressive yield strength of ∼1564 MPa and fracture strain of ∼28 %). DFT calculations were performed to elucidate relevant mechanisms. Sliding wear tests were also performed, which demonstrate superior wear resistance of the HEAs at both room and elevated temperatures, compared with a commercial Ni-based superalloy, UHT-Nickel.