Dislocation-induced dispersion of nanoparticles as a reason for the cyclic functional instability of Ni–Fe–Ga–Co alloys

In the framework of the theory of diffuse martensitic transitions the physical mechanism is discussed of the cyclic instability of the functional properties of crystals of Ni$_{49}$Fe$_{18}$Ga$_{27}$Co$_{6}$ alloy not annealed as grown subjected to thermo-mechanical cycles: compression in the [011] direction - the return of shape memory strain upon heating. Cycling leads to a decrease in compression stresses and their stabilization after 9–10 thermo-mechanical cycles. Calculations in the framework of the diffuse martensitic transitions theory show that the decrease in stresses is associated with the dispersion of nanoparticles (antiphase domains) by slip dislocations. As a result, the disordered $B_2$ structure of an unannealed crystal transforms into an ordered $L2_1$ structure, which is characteristic for crystals of this alloy annealed at a high temperature after their growth.