Hot deformation behavior of the equiatomic CoCrFeMnNi high entropy alloy
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Date
2021
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University of New Brunswick
Abstract
High entropy alloys (HEAs) are a recent discovery in the field of materials science which has challenged many traditional theories concerning the formation and properties of alloys. These new materials have been shown to have surprisingly simple structures despite their complex composition, with unique behavior unseen in traditional alloys, making them strong candidates for future applications in the aerospace and defense industries. This work focuses on the CoCrFeMnNi alloy, the most researched HEA to date. This thesis specifically examines the hot compressive deformation behavior of the equiatomic CoCrFeMnNi alloy at two strain rates, 0.01 s⁻¹ and 1 s⁻¹, when exposed to temperatures ranging from 200-800°C. The experimental results were employed to determine the constitutive model coefficients for an array of existing models, namely, the Johnson-Cook, modified Johnson-Cook, Zerilli-Armstrong, modified Zerilli-Armstrong, Zener-Hollomon, Hensel-Spittel, and modified Hensel-Spittel models. The modeling results were used to compare the precited flow stresses with those of the experimentally-obtained values through quantitative statistical means.
The modified Johnson-Cook, Zener-Hollomon, Hensel-Spittel, and modified Hensel-Spittel models were found to have the best fit with the experimental data for the studied flow stresses. To support the numerical-experimental quantitative information, microstructural characterization of the samples was performed. Results show the presence of discontinuous dynamic recrystallization in samples tested at 0.01 s⁻¹ and 800°C; thus, confirming the presence of discontinuous dynamic recrystallization under these conditions. This observation explains the stress behavior of the material at the low strain rate.