Influence of multiaxial isothermal forging on magnetocaloric effect and magnetostructural transition in Ni-Mn-Ga-Si alloy

The influence of as-cast and multiaxial isothermal forged structures on the sensitivity of martensite to the magnetic field and on the magnetocaloric effect in Ni-Mn-Ga-Si alloy has been studied. In the multiaxial isothermal forged state, a “necklace” structure is observed where large grains of 100–200 µm are encompassed by a layer of fine-grained structure. In this state, the martensitic transformation occurs with a shift towards the low-temperature region of about 10 K. Characteristic points of the martensitic transformation are evaluated in a magnetic field up to 12 T, revealing a sensitivity value of 0.6 K/T for both as-cast and multiaxial isothermal forged samples. Furthermore, an inverse magnetocaloric effect is identified within the martensitic transformation region for both as-cast and multiaxial isothermal forged samples under weak magnetic fields, up to 0.2 T. This inverse effect disappears at a magnetic field of 1.8 T, leaving only the direct magnetocaloric effect observable. These findings shed light on the intriguing interplay between microstructure, magnetic sensitivity, and magnetocaloric behavior in this Ni-Mn-Ga-Si alloy, offering valuable insights for potential applications in magnetic cooling technologies.