Thermoelastic γ-ε martensitic transformation and shape memory effect in the [001]-oriented Cr₂₀Mn₂₀Fe₂₀Co₃₅Ni₅ high-entropy alloy single crystals

The thermoelastic γ-ε martensitic transformation (MT) was studied for the first time in [001]-oriented single crystals of the Cr₂₀Mn₂₀Fe₂₀Co₃₅Ni₅ (at.%) high-entropy alloy (HEA) during cooling and heating in the free state and under tensile stress. It was hown that during cooling and heating in the free state, the γ-ε MT was characterized by a wide temperature hysteresis ΔT_h = A_f - M_s = 160 K. In the [001]-oriented Cr₂₀Mn₂₀Fe₂₀Co₃₅Ni₅ HEA single crystals with a thermoelastic γ-ε MT, the shape memory effect (SME) under tension was discovered for the first time, which depended on the test temperature and the conditions for studying the SME (isothermal or isobaric deformation).The maximum SME value of (3.6±0.2)% was found at the M_s temperature under conditions of the isothermal deformation. The SME value turned out to be less than the theoretical value of the lattice deformation ε₀ = 8% for the γ-ε MT in the [001] orientation under tension, but more than the SME in polycrystals of this alloy, 1.91%, under bending strain. It was shown that the development of ε-martensite simultaneously in several systems, a small temperature interval for the formation of ε-martensite under stress, and a high level of stresses for the implementation of γ-ε MT under stress limit the SME value in this orientation under tension.

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