In this paper, we present structure, structural phase transformation, magnetic phase transition, and magnetocaloric effect of Ni50Mn50-x Ga x (x = 17, 18, 19, 20, and 21) shape memory alloys. X-ray diffraction patterns display nano-crystalline phases in the alloys. The samples are soft magnetic material with very narrow magnetic hysteresis. The martensitic-austenite transformation temperature increases from 219 K (for x = 17) to 322 K (for x = 21) with increasing Ga-concentration. Ga also increases the Curie phase transition temperature and the saturation magnetisation of the alloy. The external magnetic field also clearly affects the structural phase transition of the alloy. The magnitude of the martensitic-austenitic phase transition decreases with the increase of the applied magnetic field. Both the normal and invert magnetocaloric effects coexist in the alloy. Under the magnetic field change of 10 kOe, the maximum magnetic entropy change, ∣ΔS m ∣max, for the Ni50Mn30Ga20 ribbon is 0.95 J.kg−1.K−1 for the normal magnetocaloric effect.

In this work, we investigated the structure, mechanical properties and corrosion resistance of Ti50Ni50 and Ti16.667Zr16.667A16.667Ni25Cu25 (A = Hf, Nb, Co, Cr and Ga) shape memory alloys (SMAs) fabricated by using melt-spinning method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses reveal that the alloy ribbons are partially crystallized with B19' martensitic structure in the added alloys. The crystalline phase formation and the atomic size difference (δ = 4.33 - 10.25%) significantly affect the hardness, tensile strength, tensile strain, elastic modulus and corrosion resistance of the alloys. The hardness of the alloy gradually increases from 583 HV to 873 HV when adding elements in the order of Hf, Nb, Co, Cr and Ga. Tensile strength, tensile strain and elastic modulus simultaneously reach their maximum of 669.2 MPa, 0.899% and 28.82 GPa, respectively, when Hf is added to the alloy. Ga enhances the corrosion resistance of the alloy ribbons more than other additional elements.

Shape memory alloys (SMAs) are ones which can return to their original shape under impact of temperature or external magnetic field. The SMAs are capable of many applications in the fields of biomedical, aerospace, microelectronics, automation, for examples, orthodontics, stents, bone anchors, automatic valves, heat sensors, nanotweezers, robots... Recently, researchers have discovered the shape memory effect (SME) on high entropy alloys (HEAs). The combination of superior properties of SMAs and HEAs (high strength, heat resistance, low diffusion coefficient...) would bring useful practical applications in practice. In this paper, we will present an overview of the research situation of SMAs and our initial results obtained on Ni-Ti based alloys of Ni-Ti, Ni-Ti-Zr-Cu-Cr, Ni-Ti-Zr-Cu-Co, Ni-Ti-Zr-Cu-Nb, and Ni-Ti-Zr-Cu-Hf prepared by melt-spinning method.