Martensitic and magnetic transformation behavior of Ni₅₀Mn_38-xIn₁₂Fe_x polycrystalline alloys

The effect of Fe substitution for Mn on the martensitic and magnetic transformation behaviors of Ni₅₀Mn_38-xIn₁₂Fe_x (x=0, 3, 4, 5, 6) polycrystalline alloys was investigated. A martensitic transformation from a B2 austenite to an orthorhombic martensite was observed with lower Fe contents (x≤4), while the transformation was completely suppressed with further increasing the Fe content (x≥5) of the alloys. Substitution of Fe for Mn at above 3%(x) introduced an fcc γ phase in the microstructure, the amount of which increased with increasing the Fe content. The γ phase influenced the composition of the matrix phase, as well as the e/a ratio, leading to a series change of the physical properties of the alloys. Firstly, the e/a ratio of the matrix phase decreased rapidly with increasing Fe content, resulting in the abrupt decrease of martensitic transformation temperature and enthalpy change. Secondly, Fe addition effectively increased the ferromagnetic ordering of the matrix phase, leading to the increase of the Curie transition temperatures and the magnetization of the alloys. The origin of the effect of Fe addition on changes in martensitic transformation and magnetic behaviour is discussed.