Study on Dynamic Tensile Mechanical Behavior and Deformation Mechanisms of CrCoNi Medium Entropy Alloy at Room and Cryogenic Temperature

doi:10.3901/JME.2022.20.350

Abstract

Abstract: The CrCoNi medium entropy alloy (MEA) has both good strength and ductility under quasi-static tension, but its dynamic tensile mechanical behavior needs further study. The split Hopkinson tensile bar is used to perform dynamic tensile tests on the CrCoNi MEA with different strain rates at room temperature (298 K) and cryogenic temperature (77 K), and a modified JC (Johson-Cook) constitutive model is established to describe the plastic flow behavior well. The deformation mechanisms of CrCoNi MEA are revealed by microstructure characterization. The tests results show that：the strength and ductility of CrCoNi MEA at room temperature gradually increase with the increase of strain rate. Compared with quasi-static tensile, when the dynamic tensile strain rate is 1 200-5 000 s^-1, the yield strength increases to 560 MPa and to 1 150 MPa, and the elongation increases to 60% and to 90%; At cryogenic temperature, the strength exhibits a similar strain rate effect and the strength is higher, but the elongation is reduced. The deformation mechanism results are：compared with quasi-static tensile at room temperature, the twins density of the samples under dynamic tension at room temperature increases and multiple twinning occurs, the FCC→HCP phase transition occurs, and the nanograins form, together promoting the improvement of work hardening of CrCoNi MEA; compared with dynamic tensile at room temperature, the excessive twin density of the samples under dynamic tensile at cryogenic temperature causes increase in twin thickness, and the nanograins form, which promote further increase in work hardening, but the increase of twin thickness enhances the hindrance to dislocations thus leading to a decrease in ductility.

Key words: CrCoNi medium entropy alloy, high strain rate, dynamic tensile at cryogenic temperature, deformation mechanism

CLC Number:

O346

CHANG Hui, ZHANG Tuanwei, WANG Jianjun, LI Zhiqiang, WANG Zhihua. Study on Dynamic Tensile Mechanical Behavior and Deformation Mechanisms of CrCoNi Medium Entropy Alloy at Room and Cryogenic Temperature[J]. Journal of Mechanical Engineering, 2022, 58(20): 350-360.

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