Microstructure and Texture Evolution During Thermomechanical Processing of Al 0.25 CoCrFeNi High-Entropy Alloy
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UCTION
HIGH-ENTROPY alloys (HEAs) are a relatively new class of materials introduced independently by Yeh et al.[1] and Cantor et al.[2] and can be defined as multicomponent alloys that contain five or more principal elements. Despite this large number of components, these alloys typically present simple and disordered solid-solution structures: face centered cubic (FCC),[2–4] body centered cubic (BCC) or a combination of FCC + BCC phases,[1,5–7] and hexagonal close packed (HCP).[8,9] Thus, the configurational entropy is maximized favoring the formation of these simple solidsolutions instead of complex intermetallic phases, which distinguishes HEAs from conventional metallic systems. Nevertheless, it is important to emphasize that this definition has been debated by many authors and still causes controversy. Miracle and Senkov[10] discussed about several multiphase alloys containing five or more
LEANDRO A. SANTOS is with the Department of Metallurgical and Materials Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, MG 31270901, Brazil. Contact e-mail: [email protected] SARANSH SINGH and ANTHONY D. ROLLETT are with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted February 28, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
principal elements, which they designate as complex concentrated alloys (CCA). HEAs have attracted scientific interest owing to their unique combination of components, which results in unusual properties, such as excellent thermal stability,[11,12] resistance to anneal softening,[13] high strength,[14,15] and high corrosion and oxidation resistance.[11,16] The thermal stability is related to the presence of different atoms at each lattice point and sluggish diffusion rates owing to the heavily distorted lattice.[17,18] The latter may affect recrystallization and grain growth since these are diffusion-based processes, resulting in slower recrystallization kinetics in comparison with other alloys.[19–21] Among a wide range of compositions that form HEAs, the AlxCoCrFeNi system is one of the most popular and has attracted much attention recently because of its promising properties.[22–28] For lower Al content, this system presents a single FCC phase. On the other hand, with the increasing of Al content, this system shows a transition from single FCC to BCC phases. Kao et al.[22] reported that this multiphase character exists for the range 0.45 £ x £ 0.88. Nevertheless, recently Liu et al.[5] found a BCC phase in an FCC matrix for the Al0.3CoCrFeNi alloy. Furthermore, HEAs with a majoritarian FCC structure exhibit low stacking fault energy, which facilitates the formation of deformation twins.[29]
Thermomechanical processes usually involve plastic deformation and subsequent annealing, resulting in the refinement of microstructure and the development of texture.[3,4,20,30,31] Despite the extensive literature on the processing of these alloys, there are only a few works focused on the microstructure and text
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