Microstructure And Martensitic Transformation Of Ga-mn-ni-co Alloys

The microstructure, martensitic transformation and magnetic properties of Ga-Mn-Ni-Co magnetic shape memory alloys and its aging alloys have been studied by means of optical microscope, XRD, TEM, DSC and VSM. The effect of Co addition and aging on microstructure, martensitic transformation temperature and magnetic properties have been discussed.It is shown that the Ga-Mn-Ni-Co alloys is austentic phase at room temperature after quenching the sample in ice water from solution-treated at 600℃for 48 hours. But we can get martensitic phase at room temperature after multi-stage heat treatment(600℃for 48 hours then at 450℃for 24 hours), and the Ms is 474℃.The experimental results show that the martensitic transformation temperatures and lattice constant in Ga₅₀Mn₂₅Ni_25-xCo_x(x=0.2,0.5,1,2,5) alloys are significantly influenced by Co content. The martensitic transformation temperatures rise slouly when Co content is less than 0.5at%;and the martensitic transformation temperatures decrease when Co content is more than 0.5at%. Co doping(<5at%) do not change the type of martensite which is 7M monoclinic structure, and appropriate aging treatment can significantly effect the phase transition temperature,Ms decreases as the aging temperature increase, and Ms decreases at first and then increase as the aging time increase.The magnetic measurements show that the saturation magnetization and magnetocrystalline anisotropy constant of austentic Ga-Mn-Ni alloys decrease with co doping, and the Co substituted Ni can improve the curie temperature. The saturation magnetization and magnetocrystalline anisotropy constant of martensitic Ga₅₀Mn₂₅Ni_25-xCo_x alloys increase at first and then decrease as the Co content increase.