Martensitic and magnetic transformation of Co41Ni32Al24Sb3 and Co41Ni32Al27 alloys
(1. School of Materials Science and Engineering, Central South University,
Changsha 410083, China;
2. State Key Laboratory of Powder Metallurgy, Central South University,
Changsha 410083, China;
3. Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan)
Changsha 410083, China;
2. State Key Laboratory of Powder Metallurgy, Central South University,
Changsha 410083, China;
3. Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan)
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 Tm and Curie point Tc are in linear relation to quenching temperature. Tm increases by 9 K and Tc increases by 7.5 K for every 10 K increasing in quenched temperature. Quenched from same temperature, Tm of Co41Ni32Al24Sb3 alloy is higher than that of Co41Ni32Al27 alloy by 76 K, meanwhile Tc 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 Tm and Tc were explained by total average s+d electron concentration and magnetic valence number Zm respectively.
Key words: ferromagnetic shape memory alloy; Co-Ni-Al-Sb alloy; martensitic transformation; Curie point