Structural and mechanical characterization of scale-up FeCoCrNi, FeCoCrNiCux, AND FeCoCrNiAlx high entropy alloys (HEAs)

Erdal, Ziya Anıl
High entropy alloys (HEAs) have recently attracted much attention due to their unique properties such as high ambient and elevated temperature strengths, hardness, and good structural stability. FeCoCrNi is one of the well-known alloy system with its excellent HEA forming ability. This alloy was previously produced by various methods using high grade pure raw materials. However, there is no scale-up production from industrial raw materials which contain various impurity elements such as Al, Si, and C. In this study, FeCoCrNi, FeCoCrNiCux, and FeCoCrNiAlx (x: 0.3, 0.6, 1) HEAs were produced from industrial grade raw materials with impurities using induction casting method. These alloys were produced by using of high purity raw materials to compare microstructural features and mechanical properties, as well. These alloys were modelled through Vienna Ab initio Simulation Package (VASP). Structural characterization were performed with X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermodynamic properties of these alloys were investigated by HEA Calculator and Thermo-Calc software. Hardness, tensile and compression tests were performed to reveal basic mechanical behavior. Cr7C3 phases were present in impure FeCoCrNi alloy besides FCC main phase, on the other hand the pure specimen had only FCC phase. 515 MPa tensile strength with 57 % ductility and 650 MPa tensile strength with no ductility were obtained for pure and impure FeCoCrNi alloys, respectively. The addition of Cu does not cause a significant structural and mechanical difference in HEAs. However, the addition of Al caused the crystal structure to transform from FCC to BCC. Impure FeCoCrNiAl0.6 alloy which has 2770 MPa maximum compressive strength with 14% compressive strain at fracture is the strongest one among produced alloys. It also shows better mechanical properties compared to Mg, Al, Ti and most of the Fe, Ni containing alloys.
Citation Formats
Z. A. Erdal, “Structural and mechanical characterization of scale-up FeCoCrNi, FeCoCrNiCux, AND FeCoCrNiAlx high entropy alloys (HEAs),” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Metallurgical and Materials Engineering., Middle East Technical University, 2020.