| In this paper, large-size bulk material Ni-Mn-Sb ternary alloys, Ni-Mn-Sb-Si quaternary alloy, Ni-Co-Mn-Sb-Si quinary alloy were prepared by induction melting method.We discussed the content design of the alloys and production process optimization, organizational structure, phase transition, magnetic properties and heat treatment, quenching which affected the subsequent ordering of the structure and its martensitic phase transformation and magnetic properties, as well as different magnetic- structure coupled with the relevant aspects of the state of design magnetocaloric effect.The research results show that,considering the uniformity of organization, phase transition temperature, magnetic and thermal hysteresis, we selected the optimum matrix for Ni50Mn38Sb12 alloy. There were four different types of martensitic variants in the microstructure, which had 4O martensitic structure. Under 5 T magnetic field, the alloy’s ? Sm was 18.11 J/kg, and magnetic hysteresis was 11.73 J/kg, as a result, the RCnet was 34.34 J/kg. Next,we doped Si element to the NMSS12 ternary alloy,which has the composition of Ni 50Mn38Sb12- x Six(x = 0.5, 1, 2, 3), the final selection of heat treatment process had two types:(1) quenching heat treatment, namely water quenching after heat preservation under 900 ゜C for 24 h;(2) ordering heat treatment: nanmely furnace cooling after preservation under 900 ℃ for 24 h, preservation under 720゜C for 2 h, preservation under 700゜C for 5h, finally preservation under 500 ゜ C for 20 h. Considering the microstructure uniformity, working temperature range, multiple factors such as magnetic hysteresis and orderly state,NMSS0.5 alloy of ordering state has optimal performance, whose ? Sm under 5T was 9.42 J/kg, and whose magnetic hysteresis was only 2.2 J/kg, thus whose RCnet was 50.13 J/kg which was much higher than NMS12 ternary alloy. In the microstructure of two kinds of heat treatment conditions of NMSS3 alloys, three phase exist, by means of EDS analysis, we obtained that the nature of three phase was one kind of matrix, and the two kinds of eutectic phase in the heat treatment process,respectively. In the heating/cooling process,there were two structure transformations at high temperature and low temperature,but at high temperature, magnetic phase transition did not proceed obviously.By means of MFM test, the alloy matrix and precipitate phase both were magnetic, so the reasons for magnetic phase transition at high temperature gentlely was the transformation temperature of precipitated phase was higher than the TC, thus phase change and the secondary phase coupled. Therefore,we continue to dope Co element to NMSS3 alloy replacing part of Ni element.The composition of alloy was Ni50-x Cox Mn38Sb9Si3(x = 6, 12) in order to improve the alloy Tc point, reducing the phase transition temperature of the precipitated phase,as a result produing the greater magnetic phase transition and improving alloy Δ Sm. The heat treatment process of alloys was:(1)water quenching after preserving under 900 ゜C for 24 h,(2) furnace cooling after preserving under 900 ゜ C for 24 h. After doping, the microstructure of alloys were similar in appearance,and the composition of NMSS3 alloy was uneven, illustrating the composition of non-uniformity still existed in the as-cast alloy.Furthermore, the EDS analysis indicated that the matrix phase actually was first eutectic phase and two kinds of precipitated phase was namely eutectic phase.The three phases did not vanish with the elevated homogenization heat treatment temperature and longer heat preservation time. The magnetic thermal performance for the quenching state Co12NMSS3 alloy showed that ? Sm is 4.68 J/kg under 5T, and the magnetic hysteresis was 4.15 J/kg, thus the RCnet was 11.9 J/kg. |
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