MARTENSITE TRANSFORMATION IN TiNi ALLOY UNDER COUPLING TEMPERATURE AND HIGH MAGNETIC FIELD USING LANDAU THEORY MODEL
Landau理论研究TiNi顺磁合金热/强磁场耦合下的马氏体相变

The martensitic transformation behavior under coupling temperature and high magnetic field in TiNi paramagnetic shape memory alloy was studied by using the modified Landau model. In order to introduce the effect of high magnetic field, the Fermi surface total density of state (DOS) of TiNi alloy under different phase--transformed shear strain (order parameter) was calculated by using the first--principles calculations, then the relationship between magnetic susceptibility and shear strain was carried out. The calculation results from the modified Landau model involving the effect of magnetic free energy indicated that the martensitic transformation temperatures (Ms and T0) suddenly increase. It can be mainly contributed to the parabola increasing of martensitic transformation driving force under coupling temperature and high magnetic field. Also, it is found that the oriented growth of martensitic variants occurs under coupling temperature and high magnetic field due to the increased difference of free energy between variants, which is consistent with the TEM observation that some vertical two--variants are present in TiNi alloy under 5 T magnetic field.