Martensitic phase transformation and magnetic transition of β based Ni₅₂Ga₂₈Fe_20-xCo_x alloy

The effects of Co concentration x on the martensitic transformation and magnetic properties of Ni₅₂Ga₂₈Fe_20-xCo_x alloys were investigated by optical metallography, SEM, XRD, DSC and VSM methods. The results show that the martensitic transformation temperatures of Ni₅₂Ga₂₈Fe_20-xCo_x alloys elevate greatly with the increase of x. The increase of x leads to the increase of martensitic transformation temperatures by 50 K~60 K in the range of x ≤ 6, but their Curie points. It has hardly any effects on martensitic transformation temperature but makes Curie points increasing by 20 K~30 K when the quench temperature fell down from 1423 K to 773 K due to the increase of order degree of mother phase from B2 → L2₁ transformation. The X-ray diffraction patterns of powder sample show that only the L1₀ (2M) type martensitic phases appears in alloys quenched from 1423 K or 773 K, but the XRD pattern of bulk sample shows that the Ni₅₂Ga₂₈Fe₁₇Co₃ alloy has a 14M type martensite. It is also found that the martensitic transformation temperature decreased and the depositing of γ phase increased by this powder process.