| The amorphous alloys with short range order and long range disorder structure possess many unique properties. Among those alloys, Fe-based amorphous alloys have high magnetic permeability and saturation magnetization, low coercivity and other excellent soft magnetic properties. As a kind of magnetic refrigeration materials, the high electrical conductivity and good thermal conductivity of Fe-based amorphous alloys result in decreasing eddy current losses effectively and increasing heat exchange rate between magnetic refrigerator and fluid. Fe-based amorphous alloys also display some advantanges such as tunable ordering temperature, large magnetic order transition range and low cost of raw materials, which makes Fe-based amorphous alloys as a potential magnetic refrigerant near room temperature.Finemet type alloys, whose typical composition is Fe73.5Si13.5B9Cu1Nb3, are the earliest known Fe-based amorphous and nanostructure alloys. In this disertation, the composition of Fe78Si4Nb5B12Cu1 alloy is used as the basic compositon. First of all, the influences of the doping of light rare earth elements La, Pr on the structure, thermal stability, magnetic properties and magnetocaloric effect of Fe-Si-Nb-B-Cu alloys have been investigated. The results show that amorphous structures were obtained for all the alloys by using single-roller melt-spinning method. The doping of La and Pr has little effect on the glass formation ability of the amorphous structure, but could improve the thermal stability effectively. Under an applied magnetic field change of 1.5 T, the maximum magnetic entropy changes(-ΔSM) of Fe78-xPrxSi4Nb5B12Cu1(x=0, 1, 3, 5, 10) are 1.38, 1.38, 1.72, 1.49, 1.36 J·kg-1K-1, respectively, which are lower than those of the first order magnetic transition materials. However, when the content of Pr doping with x=3, the magnetic entropy change(-ΔSM) value is larger than that of Nanoperm type alloy Fe88Zr7B4Cu1(-ΔSM=1.32 J·kg-1K-1).Different from the doping effect of the La and Pr element, the Curie temperature and maximum of(-ΔSM) for Fe78-xCexSi4Nb5B12Cu1(x=0, 1, 3, 5, 10) amorphous alloys decrease with increasing Ce content. The values of Curie temperature(TC) are 305 and 281 K with x=5 and x=10, respectively, which are near room temperature. There are three methods used to prepare the composite materials by using the alloys with x=1, 3, 5 and 10. That is, the composite was prepared by simply stacking the ribbons together, named as Com 1#; The composite was prepared by fabricating the ribbons together with silver colloid as the binder, denoted as Com 2#; And the composite Com 3# was prepared by manually grinding the ribbons to powders and mixing them together. The results show that more broad magnetic entropy change peak could be obtained in these aforementioned composites, the maximum(-ΔSM) remains a constant value in a large transition temperature range, and the range is nearly 80 K(from 275 to 355 K). Under the magnetic change from 0 to 5 T, the values of RC and ΔTFWHM(full width at half maximum of the-ΔSM vs. T curves) for the three composites are 318, 317, 273 J·kg-1 and 203, 196, 200 K, respectively. Large RC and ΔTFWHM make the Finemet type Fe-based amorphous alloys be a promising magnetic refrigerant for magnetic refrigeration based on Ericsson cycle.Finally, the effects of doping heavy rare earth elements Gd and Dy on the magnetic properties and magnetocaloric effect in Fe78-xRExSi4Nb5B12Cu1(RE=Gd, Dy) amorphous alloys were investigated. The results indicate that the TC values could be tuned continuously in a large temperature range, the effective magnetic moment values of Fe78-xRExSi4Nb5B12Cu1(RE=La, Pr; x=0, 1, 3, 5, 10) alloys calculated with Curie-Weiss law are 4.18, 6.04, 3.49, 3.16, 3.1 μB(for Gd) and 4.18, 7.14, 5.24, 4.42, 3.8 mB(for Dy), respectively. The tendency of(-ΔSM) for those alloys is positively associated with the effective magnetic moment. Under the applied field change of 1.5 T, the values of(-ΔSM) in Gd and Dy doping alloys with x=1 are 1.66 J·kg-1K-1 and 1.74 J·kg-1K-1, respectively. Low cost, continuously tuneable Curie temperature and large magnetic entropy change make Fe78-xRExSi4Nb5B12Cu1(RE=Gd, Dy) amorphous alloys have great application prospects as one of magnetic refrigeration materials working near room temperature. |
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