The Structure Transformation And Magnetic Properties Of Cu Doped NiMnIn Alloys

Ni-Mn-In alloys is a new kind of magnetic shape memory alloys. Researches mainly focus on two aspects:the first is the magnetic induced strain, which is the fundamental of alloy deformation, while the research of the martensite is the basis; the other is the magnetocaloric effect, this is fundamental of magnetic refrigeration, so because of the properties, the alloy is also used as magnetic refrigerant.Because Ni-Mn-In alloys are very sensitive to the changes in the composition, and depend on the scholars’recent research over the world. This paper decides to dope Cu to change the composition of two different systems. The paper mainly use the optical microscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), vibrating sample magnetometer (VSM) and universal mechanical testing machine on the studies of Ni50-xMn4oInioCux (x=0,1,2,4,5,6,8) alloys and their ribbons. The study includes the microstructure, phase structure, martensite and austenite transformation temperature, magnetic properties and compression performance. It also focuses on the research of the phase transition activation energy and the magnetocaloric effects of Ni50Mn35_xIni5Cux (x=0,1,2,3,4,5) alloys and ribbons.The research shown that Ni50-xMn4oIn10Cux (x=0,1,2,4,5,6,8) alloys and ribbons are the mixed composition of martensite and austenite. The main structure is a modulated structure of 7M martensite. As the increase of the Cu, Ni50-xMn4oIn10Cux (x=0,1,2,4,5,6,8) alloys and ribbons have shown the martensite transformation obviously. Phase transition temperature decreases with Cu doping, and the temperature finally is below room temperature. Martensitic transformation temperature is always lower than the austenite phase transition temperature, which is the thermal hysteresis phenomenon. The effect of the rate on the transformation temperature mainly consists of three stages, the low-speed zone, medium zone, and the high-speed area. In the three stages, the phase transition temperature changes significantly.By studying Ni50Mn35-xIni5Cux (x=0,1,2,3,4,5) ribbons’s phase transition activation energy, we found that the alloys are a first-order phase change materials. Through the calculating of non-isothermal kinetics, we found that the martensitic transformation process is divided into two phases, the phase transitions initial nucleation stage and a first-order martensitic phase transformation.By studying Ni5oMn35-xIni5Cux (x=0,1,2,3) bulk’s magnetic entropy, we find that the magnetic entropy has a significant change with the Cu doping. When the Cu content is lat%, the magnetic entropy is the biggest. Through its Arrott curve found that near the martensitic transformation temperature occurs the variable magnetic phase transition, and the alloy is a typical first-order phase transition.