Development of a Refractory Hexagonal Closed Packed High Entropy Alloy Based on Thin Film Screening
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.114
Development of a Refractory Hexagonal Closed Packed High Entropy Alloy Based on Thin Film Screening Azin Akbari1 and T . John Balk 1 1
Department of Chemical and Materials Engineering, University of Kentucky, 177 F. Paul Anderson Tower, Lexington, KY 40506, USA
In order to identify candidate high entropy alloys (HEAs) that have the hexagonal closed packed crystal structure, gradient thin films in the OsRuWMoRe system were deposited by sputtering from multiple elemental targets onto Si substrates. In addition to having compositional gradients, the films exhibited regions with different phases, some of which were single-phase and non-equiatomic. Such alloys have the potential to exhibit properties superior to the primarily equiatomic HEAs that have been the focus of most work in this area. To screen the phases that exist across the thin film gradient samples, a range of characterizatio n techniques were employed, including focused ion beam and scanning electron microscopy, X ray energy dispersive spectroscopy, X-ray diffraction and electron backscattered diffraction analysis. The combinatorial method described in this study enabled the identif ication of a candidate single-phase HEA that was subsequently fabricated as a bulk alloy.
INTRODUCTION: High entropy alloys (HEAs) are a relatively new group of multicomponent materials with a complex chemistry [1,2]. HEAs contain five or more unique principal elements, with the content of each alloying component in the range of 5-35 at.% and with configurational entropy of 1.5R or higher, where R is the gas constant. The alloy development research community has been working to identify single-phase HEAs over the past several years [3]. M ost of the alloy systems discussed in the literature have cubic crystal structures. However, there has been relatively little research focus on HEAs with the hexagonal closed packed crystal structure (HCP) [4]. Takeuchi et al. and other groups have worked on the fabrication of HCP HEAs with high melting points for refractory applications, including alloys such as YGdTbDyLu and GdTbDyTmLu [5]. Whereas most of these alloy systems contain lanthanide metals, the OsRuWM oRe alloy system studied in this paper is one of the few HCP systems that contains only transition metals.
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HEAs are different from conventional alloys, in that they have no single element that serves as the majority or solvent element. Instead, HEAs contain five or more elements, each with a significant atomic fraction. This leads to a vast number of possible alloy compositions, resulting in a daunting effort required for HEA discovery and development via conventional metallurgical techniques. The scientific literature provides examples of successful HEA development using appro
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