Thermoelastic Martensitic Transformation and Shape Memory Effect in [001]-Oriented Single Crystals of High-Entropy Alloy

For the first time, this paper studies thermoelastic γ–ε martensitic transformation in [001]-oriented single crystals of the Cr 20 Mn 20 Fe 20 Co 35 Ni 5 high-entropy alloy during cooling/heating under free state and tensile loading. It is shown that during cooling/heating in free state, the γ–ε martensitic transformation is characterized by a wide thermal hysteresis (ΔT h = A f – M s = 160 K). The shape memory effect is discovered for the first time in the [001]-oriented single crystals of this alloy under tensile stress, with the thermoelastic γ–ε transformation. This effect depends on the test temperature and studied conditions (isothermal or isobaric deformation). The maximum shape memory effect of 3.6±0.2% is observed at a martensitic transformation temperature during isothermal deformation. The shape memory effect is lower than the theoretical value of 8% of the lattice deformation for the γ–ε transformation in the [001] orientation under tensile stress, but it is higher (1.91%) than in polycrystals of this alloy under bending deformation. It is shown that this shape memory effect is limited by the development of ε-martensite in several systems simultaneously, low temperature range of stress-induced ε-martensite, and a high stress level of the γ–ε transformation.