Martensitic And Magnetic Transformation Behaviors In NiMnIn(Co) Metamagnetic Shape Memory Alloys

Ni₅₀Mn_25+XIn_25-X,Ni₄₅Co₅Mn_25+XIn_25-X,Ni_42.5Co_7.5Mn_25+XIn_25-X alloys were melting by vacuum arc furnace under an argon atmosphere. The martensitic and magnetic behaviors of the alloys were investigated by differential scanning calorimetry (DSC) , vibrating sample magnetometry (VSM), X-ray diffraction (XRD) and scanning electron microscope (SEM). The relationship between composition electron concentration and the martensitic transfomation temperature were be studied. The article focused on the effect between the composition with the martensite morphologies and the magnetic properties durning the reverse martensitic transformation under magnetic field.The results show that: The martensite transformation temperature of NiMnIn (Co) alloys have close contact with the composition and electron concentration of the alloys. In this paper, the designed electron concentration is from 7.90 to 8.02. In the three series NiMnIn(Co) alloys, the martensitic transformation starting temperature (Ms) decreases with increasing In composition and decreasing electron concentration. On the other hand, the addition of Co resulted in a decrease of Ms. During the cooling and heating process, the martensitic transformation and the reverse martensitic transformation can be observed. In addition, the mid-martensitic transformation was investigated in Ni₄₆Mn₄₁In₁₃.The structure of NiMnln (Co) alloys is L2₁ body-center cubic parent phase and the different monoclinic martensitic phase at room temperature. The microstructure of martensitic Ni₅₀Mn_25+XIn_25-X alloys is full of spearhead-shaped martensite which have good co-cooperation effect. The DSC indicate that the bigger latent heat of crystallization will gain better microstructure of martensite, which in this experiment has been verified. The addition of Co resulted in abundant form, including spearhead-shaped martensite,thin plate-shaped martensite,lentoid-shaped martensite,papilionaceous-shaped martensite and bamboo-shaped martensite.NiMnIn (Co) are ferromagnetic alloy at room temperature, the ferromagnetic decreases with the increase of In composition, but the addition of Co had little impact. The reverse martensitic transformation temperature increases inducing by magnetic field. The inverse transformation from the paramagnetic or the antiferromagnetic martensite phase to the ferromagnetic parent phase finally into paramagnetic austenite were investigated under the magnetic field.