Elemental Effects on Weld Cracking Susceptibility in Al x CoCrCu y FeNi High-Entropy Alloy
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THE concept of high-entropy alloys (HEA) introduced a new way of advanced materials development. High-entropy alloys are defined as multi principal element alloys usually composed of five or more alloying elements (from 5 to 35 at. pct each).[1] This is radically different from conventional micro-alloying strategies enabling properties that far-surpass that of conventional alloys. Until recently, most HEA research aimed to provide a fundamental understanding of high-entropy alloy processing, microstructures, and mechanical behavior. The focus is shifting to more carefully designed high-entropy alloys that possess multiple phases and tailored microstructures in order to achieve a unique set of properties relevant to specific industrial applications.[2] However, an engineering design approach imposes additional constraints onto the HEA development process. Besides good mechanical behavior, structural applications may require many other properties, including the ability to be joined and formed into complex shapes.[3] Welding is a critical ALEXANDER C. MARTIN and CAROLIN FINK are with the Department of Material Science and Engineering, Welding Engineering Program, The Ohio State University, 1248 Arthur E. Adams Drive, Columbus, OH 43221. Contact e-mail: fi[email protected] JOA˜O PEDRO OLIVEIRA is with the Department of Mechanical and Industrial Engineering, New University of Lisbon, 2829-516 Caparica, Portugal. Manuscript submitted June 26, 2019.
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manufacturing process for structural components. Therefore, it is essential to address the weldability of candidate structural high-entropy alloys in the alloy development process. This can enable enhancement of weld properties, and early avoidance of adverse issues related to welding by modification of composition or microstructures during an application-driven HEA design. Little attention has been paid to high-entropy alloy welding metallurgy and weldability. Non-equilibrium conditions will significantly alter microstructures and weld properties in the fusion zone and heat-affected zone in these materials, but have not yet studied in detail. High-temperature applications are particularly interesting for alloy development based on the high-entropy concept. Among several types, the AlCoCrCuFeNi alloy system has been studied in detail due to some alloy compositions exhibiting thermal stability of microstructure and strength retention up to temperatures of 800 C,[1,4,5] High elevated temperature strength and good wear resistance make these alloys potential candidates for applications in structural and tool industries.[5] AlxCoCrCuyFeNi alloys (x and y values in molar ratio) show a gradual change from single FCC phase to mixed FCC and BCC phase, and to single BCC phase with increasing Al content. This structural change is accompanied by a significant increase in hardness.[5,6] Copper was found to strongly segregate in this alloy system due to its high enthalpy of mixing with other elements.[7,8] This shifted emphasis to alloy compositions with lo
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