Hot deformation behavior of the high-entropy alloy CoCuFeMnNi
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NANOCRYSTALLINE HIGH ENTROPY MATERIALS: PROCESSING CHALLENGES AND PROPERTIES
Hot deformation behavior of the high-entropy alloy CoCuFeMnNi Natasha Prasad1, Nitish Bibhanshu1, Niraj Nayan2,a), Ganesh S. Avadhani1, Satyam Suwas1 1
Department of Materials Engineering, Indian Institute of Science, Bangalore-560012, India Materials and Mechanical Entity, Vikram Sarabhai Space Centre, Thiruvananthpuram-695022, India a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 31 July 2018; accepted: 6 December 2018
In the present study, hot deformation behavior of a FCC high-entropy alloy CoCuFeMnNi has been investigated to explore the stress–strain response for a wide range of temperatures and strain rates. The deformation response has been examined by plotting a processing map and examining the evolution of microstructure and texture in each of the temperature–strain rate domain. Hot compression tests were carried out in the temperature range 850–1050 °C at strain rates varying from 0.001 s1 to 10 s1. Stress–strain curves indicate characteristic softening behavior due to dynamic recrystallization (DRX). DRX has been observed along grain boundaries, shear bands, as well as in the interior of deformed grains. The size of dynamically recrystallized grains shows a strong dependence on deformation temperature and increases with temperature. A high degree of twin formation takes place in the DRX grains evolved inside the shear bands, and the extent of twinning decreases at high temperatures. The optimal processing window has been estimated based on strain rate sensitivity and has been validated with detailed analyses of microstructure and texture. The best region for thermo-mechanical processing has been identified as in the temperature range 850–950 °C at strain rate 101 s1.
Introduction High-entropy alloys (HEA) are foreseen as candidate materials for application in the fields of aerospace, ship building, and machinery [1, 2, 3, 4]. These alloys primarily consist of five or more constituent elements, almost in equiatomic proportion, that form simple solid solutions (FCC/BCC or both) instead of complex intermetallics [5, 6, 7, 8]. These alloys are known to display outstanding properties such as high strength at elevated temperature, thermal stability over a wide range, excellent fracture toughness, and oxidation resistance [5, 9, 10, 11, 12]. Owing to their wide range of thermal stability, these alloys exhibit excellent elevated temperature properties as well as cryogenic properties [5, 13]. The reason for such a wide range thermal stability of these alloys is the high configurational entropy. The high configurational entropy leads to reduced free energy of the system and sluggish diffusion that slows down the process of phase transformation and complex phase formation [14, 15, 16, 17, 18]. Recently, Tazuddin et al. [19] have proposed a new HEA CoCuFeMnNi which has a single-phase FCC structure at room
ª Materials Research Society 2019
temperature as well as at high temperatures (above 850 °C).
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