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ltiphase alloys such as alpha-beta Ti alloys, dual-phase (DP) steels, and super alloys have delivered strength and toughness in many structural applications. The design of alloys with multiple principal elements generates the possibility of developing materials with unique properties and microstructural characteristics.[1] High-entropy alloys (HEAs) with multiphase microstructures[2] exhibit good combinations of mechanical properties. High-entropy alloys with microstructures analogous to those of DP or TRIP steels have been reported in the literature.[3] Eutectic HEAs (EHEAs) form a class of HEAs that are expected to possess good strength as well as ductility owing to their characteristic microstructure.[4,5] The good castability and strength of EHEAs have rendered them promising candidates for future high-temperature applications.[6,7] High-entropy alloys show sluggish diffusion,[8] which reduces the rate of coarsening of the eutectic microstructure. This ensures better mechanical properties due to the fine interlamellar spacing that promotes alloy strength in line with the Hall–Petch relation. The design of EHEAs with five elements is reported in the literature, and such alloys exhibit better

M.R. RAHUL and GANDHAM PHANIKUMAR are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India. Contact e-mail: [email protected]. Manuscript submitted January 24, 2019.

METALLURGICAL AND MATERIALS TRANSACTIONS A

mechanical properties than the conventional alloys do.[9–12] Different methods to determine the eutectic composition domains, including the mixing enthalpy and binary eutectic domains, have been reported.[13,14] A combination of primary phase and eutectic region confers an optimal combination of strength and ductility compared to a fully eutectic structure.[10] Proper selection of elements is required to design EHEAs with properties that can be explored for use in structural as well as high-temperature applications. The design of alloys with high-entropy phases can be explored in the EHEA domain to obtain stable microstructures. In this study, we explore a eutectic alloy with face-centered cubic (FCC) and Laves (C14 Laves) phases to provide the desired mechanical properties and stable microstructure. High-entropy alloys with entropy stabilization can be explored if the number of elements were to be increased. A non-equiatomic alloy 35Fe10Co25Ni15Cr10V5Mn with single-phase composition with a large FCC domain was reported recently.[15] The alloy shows enhanced cryogenic as well as structural properties. In this alloy, the atomic percentage of Fe is close to the maximum concentration limit of the high-entropy domain. The eutectic alloy was designed by replacing Fe with elements that destabilize the single phase. In this study, a eutectic alloy with seven components was designed and verified using experimental studies guided by CALPHAD tools. The eutectic alloy was designed by adding Nb to the single-phase alloy. Nb is an element that forms eutectic systems