Combinatorial thin film screening to identify single-phase, non-equiatomic high entropy alloys in the MnFeCoNiCu system
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Combinatorial thin film screening to identify single-phase, non-equiatomic high entropy alloys in the MnFeCoNiCu system Azin Akbari and Thomas J. Balk, Department of Chemical and Materials Engineering, University of Kentucky, 177 F. Paul Anderson Tower, Lexington KY 40506, USA Address all correspondence to Thomas J. Balk at [email protected] (Received 9 January 2019; accepted 11 April 2019)
Abstract To identify new face centered cubic high entropy alloys (HEAs), MnFeCoNiCu thin film samples were prepared by simultaneous magnetron sputtering of elements onto Si wafers. This sputtering arrangement yielded compositional gradients in the samples. The films exhibited regions with different phases, some of which were single-phase and non-equiatomic. To screen the crystal structure and composition across film samples, multiple characterization techniques were used: scanning electron microscopy, focused ion beam, energy-dispersive x-ray spectroscopy, x-ray diffraction, and electron backscattered diffraction analysis. Using this combinatorial method, candidate single-phase HEAs were identified and then successfully arc-melted in bulk form, followed by thermomechanical processing.
High entropy alloys (HEAs) are a relatively new group of materials[1,2] with a wide range of potential applications. Specifically, face centered cubic (FCC) HEAs have been shown to maintain their ductility and strength at cryogenic temperatures.[3–5] In addition to compelling mechanical properties, their corrosion resistance can make certain HEAs ideal candidates for structural applications in more demanding settings such as marine environments.[6] HEAs contain five or more unique principal elements, with the content of each alloying component in the range of 5–35 at.% and with a configurational entropy of 1.5R or higher, where R is the gas constant.[7] Cantor alloys[2] and Cantor-like alloys have received significant interest within the research community.[7–9] These HEAs typically contain some mix of the elements Mn, Fe, Ni, Co, Cu, and/or Cr. Addition of other alloying elements such as Al, or deviation from an equiatomic composition, has been explored as well.[5,10–12] A variety of resultant crystal structures can be achieved by minor changes to alloy compositions. Kao et al. have studied HEA crystal transformations from FCC to body centered cubic (BCC) induced by minor additions of Al to the alloy FeNiCoCr,[13] which significantly affected the mechanical properties of the alloy. Furthermore, relatively few studies have explored the addition of Cu to this family of alloys.[14,15] The current study focuses on the MnFeCoNiCu alloy system, in order to screen for candidate non-equiatomic single-phase HEAs. Unlike conventional alloys, HEAs do not have a single majority element that serves as a solvent, and this can complicate the development of new HEAs when using conventional techniques. Conventional alloy development approaches
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typically involve iteration within the context of general guidelines. When applied to HEAs, this approach c
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