Abstract: The martensitic transformation and magnetic property of Co₄₁Ni₃₂Al₂₇ and Co₄₁Ni₃₂Al₂₄Sb₃ alloys were investigated by optical microscopy(OM), scanning electric microscopy(SEM), energy dispersive X-ray spectroscopy(EDS), X-ray diffractometry (XRD), differential scanning calorimeter analysis(DSC) and vibration sample magnetometer(VSM) methods. The results show that martensitic crystal structure of Co₄₁Ni₃₂Al₂₄Sb₃ alloy is still L1₀ type. Both martensitic transformation temperature T_m and Curie point T_c are in linear relation to quenching temperature. T_m increases by 9 K and T_c increases by 7.5 K for every 10 K increasing in quenched temperature. Quenched from same temperature, T_m of Co₄₁Ni₃₂Al₂₄Sb₃ alloy is higher than that of Co₄₁Ni₃₂Al₂₇ alloy by 76 K, meanwhile T_c is higher by 18 K. The melting point of Co-Ni-Al alloy is decreased by the Sb addition, eutectic structure appears in Co₄₁Ni₃₂Al₂₄Sb₃ alloy annealed at 1 573 K, which indicates that the alloy is partially melted, whereas Co₄₁Ni₃₂Al₂₇ alloy can be annealed at 1 623 K without melted. The martensitic transformation temperature range of Co₄₁Ni₃₂Al₂₄Sb₃ alloy is 22−29 K, only half that of Co₄₁Ni₃₂Al₂₇ alloy. This is a very important result to benefit the achievement of large magnetic field induced strain on Co-Ni-Al based alloy. The results of T_m and T_c were explained by total average s+d electron concentration and magnetic valence number Z_m respectively.

Key words: ferromagnetic shape memory alloy; Co-Ni-Al-Sb alloy; martensitic transformation; Curie point