Study On Martensitic Transition Temperature And Microstructure Of Ni-Mn-Sn Alloy

The refrigeration technology has been widely used in our daily life and industrial production. Now, more attention on environment protection is given. People try to improve the destruction of the ozone layer for the traditional way of refrigeration and try to seek new technology to replace the traditional refrigeration.In this research, we discusses the martensite phase transformation characteristics of magnetic refrigeration material Ni-Mn-Sn alloy, combined with the organization of the morphology, crystal structure and phase change process, the following content is studied:(1) The martensitic transition of as-cast Ni5oMn37Sn13 alloy. Severe segregation is observed in as-cast sample. Sn is rich on the dendtrite core and Mn is rich in the interdendrite. The segration leads to the extending of martensitic transition temperature range. Homogenizing annealing decreased the composition segration between dendtritecore and interdendrite, which shirinked the martensitic transition temperature range.(2) The homogenizing annealing of as-cast Ni5oMn37Sn13 alloy after annealed at 900℃, for 2 h and 48 h, respectively. It demeonstrats that, more annealing time, more homogenous of the alloy, little viriation of the lattice parameter, and more volume fraction of martensit is formed at the romm temperature.(3) The homogenizing annealing of as-cast Ni50Mn37Sn13 alloy after annealed at 900℃, 950 ℃ and 1000℃ for 48h, respectively. Higher annealing temperature leads composition more homogeneous, larger crystal, less crystal interface and lower interface energy, lower energy barrier of martensitic transition, and more volume fraction of martensitic at room temperature.(4) The cooling rate after homogenous annealing for as-cast Ni50Mn37Sn13 alloy. After annealed at higer cooling rate.