Effect of treatment by isothermal forging on martensitic transformation in the Ni-Mn-Ga Heusler alloys

In the region of the martensitic transformation, Heusler alloys demonstrate the ferromagnetic shape memory effect, the magnetocaloric effect, etc., which allows classify them as promising functional materials. The disadvantage of alloys is their tendency to the brittle fracture during repeated thermal cycling in the temperature range of the martensitic transformation. This work presents the results of a study of the effect of isothermal forging with a high degree of the total deformation (e = 3.9) upon drawing on the microstructure and temperatures of martensitic and magnetic phase transformations of the Heusler alloy Ni$_{57.4}$Mn$_{18.2}$Ga$_{22.7}$Si$_{1.7}$. It is shown that after forging a two-component microstructure is formed, consisting of large equiaxed grains of the order of 100 m, surrounded by an interlayer of a fine-grained structure. The study of the characteristic temperatures of the martensitic transformation by the method of differential scanning calorimetry demonstrates the shift of the points of the phase transformation to the region of lower temperatures by 30–40${}^{\circ}$C. There is no significant effect on the ferromagneticparamagnetic transition temperature is observed. Thus, forging makes it possible to obtain a material with a specific microstructure, which should improve the operational properties of the material.