Effect of V content on the microstructure and mechanical properties of HPT nanostructured CoCrFeMnNiV_x high entropy alloys

Abstract

The paper presents investigations of microstructure and low-temperature mechanical properties of nanostructured alloys CoCrFeMnNiV_x (x = 0.15 – 0.75), processed by high-pressure torsion (HPT) at temperatures of 300 and 77 K. While at × ≥ 0.5 the values of microhardness (H_v) and compression yield stress (σ_0.2) in samples after HPT at 77 K are larger than those in samples after HPT at 300 K, for × ≤ 0.2 surprisingly the opposite effect is observed. As in case of the undeformed CoCrFeMnNiV_x alloys, the behaviour for vanadium concentrations × ≥ 0.5 can be related to the formation of tetragonal σ-phase in addition to fcc matrix, while the anomalous behaviour for × ≤ 0.2 arises from the formation of HPT-induced hexagonal martensitic phase. In the low temperature ranges, i.e. 20 – 300 K in case of HPT nanostructured CoCrFeMnNiV_0.2, and 150 – 300 K in case of HPT nanostructured CoCrFeMnNiV_0.5, dependences of σ_0.2(T) show characteristics of thermally-activated dislocation movement. For the first time in HEAs - anomalous dependences of σ0.2(T) at temperatures 4.2 – 20 K for CoCrFeMnNiV_0.2, and at 80 – 150 K for CoCrFeMnNiV_0.5 are found which indicate at the occurrence of non-thermal inertial dislocation movement.

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Identifiers

ORCID for Yi Huang: orcid.org/0000-0001-9259-8123

ORCID for Terence G. Langdon: orcid.org/0000-0003-3541-9250

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