The influence of structural state on cyclic stability of the two-way shape memory effect in [001]-Oriented single crystals of the coniga alloy

A study was carried out of the effect of crystal structure on the two-way shape memory effect (TWSME) and its cyclic stability using ferromagnetic single crystals of the Co49Ni21Ga30 alloy (at A), oriented along the [001]-direction, after quenching (T = 1423 K, 0.5 h) and stress-free ageing (T = 623 K for 3 h). The TWSME in [001]-oriented single crystals of the Co49Ni21Ga30 alloy was manifested after training of samples (luring implementation of B2-L l(0) martensitic transformation (MT) in the cooling/heating cycle, with constant external stress vertical bar sigma(ext)vertical bar. The value of the TWSME was found to depend on the structure of the crystals and the level of applied stress during training. The maximum TWSME value (epsilon(TWSME) = -4.3(+/- 0.2)%) was achieved after training at vertical bar sigma(ext)vertical bar = 125 MPa in single-phase crystals and was equal to lattice deformation epsilon(0) in MT for [0011 -oriented single crystals under compression. Ageing lead to a decrease in the TWSME value compared with the single-phase state in three times. In [0011 -oriented single crystals with gamma'-phase particles, the value of TWSME epsilon(TWSME), the temperature hysteresis Delta T-TWSME, and the start temperature of the forward MT M-s remained unchanged for 500 cycles, and in quenched crystals, up to 150 cycles.