Influence of Process Parameters on Microstructure Evolution During Hot Deformation of a Eutectic High-Entropy Alloy (EHE
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GH-ENTROPY alloys (HEAs) are a new class of alloy materials, introduced independently by Yeh[1–4] and Cantor.[5] HEAs have gained much attention in the last few years because of their unique properties, such as high strength[6] and ductility,[7] corrosion resistance,[8] excellent high wear properties,[9] and extraordinary cryogenic and elevated temperature properties.[10,11] This is due to their core effects such as the
M. ZAID AHMED, D. SHAHRIARI, and M. JAHAZI are with the Department of Mechanical Engineering, E´cole de technologie supe´rieure (E´TS), 1100 Notre Dame Street, West, Montreal, Quebec H3C 1K3, Canada. Contact e-mail: [email protected] K. CHADHA is with the Planetary and Space Science Centre, University of New Brunswick, NB E3B5A3, Canada. S. R. REDDY and P. P. BHATTACHARJEE are with the Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad (IITH), Hyderabad, 502285, India. Manuscript submitted November 9, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
configurational entropy, distorted lattice, cocktail effect and sluggish diffusion.[12–15] In general, these alloys contain five or more elements in their composition in equiatomic or near-equiatomic proportions. However, in recent years, minor additions of other elements have resulted in significant changes to their microstructure and properties. For example, the addition of Al has transformed the single-phase FCC HEA into a twophase FCC + BCC or a combination of FCC + BCC + B2 (ordered) phases.[16,17] These two-phase HEAs possess better mechanical properties than single-phase alloys because of the combination of different crystal structures.[18,19] Among such two-phase HEAs, AlCoCrFeNi2.1 is one with excess Ni content and a eutectic lamellar morphology called eutectic high-entropy alloy (EHEA). These alloys possess lower yield stress, high strain hardening and ductility in the as-cast form. The high strength and high ductility of the AlCoCrFeNi2.1 eutectic high-entropy alloy results from the combination of ductile L12 and the hard and brittle B2 ordered phases. These superior properties can be compared with
those of Ni-based superalloy INCONEL 600.[20] TEM characterization of uniaxial deformed specimens revealed that the L12 phase was deformed by planar dislocation slip, with a slip system of {111} h110i and low stacking fault energy, whereas Cr rich nano-precipitates strengthen the B2 phase.[21] Thermo-mechanical processing (TMP) of single- and dual-phase HEAs has shown significant improvement in the mechanical properties compared to as-cast HEA materials.[22–26] Among dual-phase materials specifically, TMP of EHEA showed the development of a micro-duplex structure with an ordered B2 phase and exceptional grain growth resistance up to 1300 C because of sluggish diffusion, resulting in a simultaneous increase in both strength and ductility.[25,26] The deformation heterogeneities such as shear bands were considered major mechanisms responsible for the observed disordering of L12 phase in EHEAs during cold d
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