稀土基原位复相多晶磁致冷材料研究

There exist many ferromagnetic alloy phases such as RAl2, RCoAl, and RNiAl as well as the multi-phase compositions including the ferromagnetic phases in the R-Co-Al and R-Ni-Al (R=Gd,Tb,Dy,Ho,Er) ternary phase diagrams. We suggest to prepare the composite magnetocaloric materials based on the ternary diagrams through in situ method in this proposal.The central idea of the method is that the multi-phase structure with good magnetocaloric effect (MCE) can be obtained in the as-cast and heat treated situations. Furthermore, the "table-like" MCE , which is necessary for the Ericsson cycle for the magnetic refrigerator working above 20K, can be realized by the optimization of the composition and microstructure. Our new materials with multi-phase structure will benefit the regerative balance, the enhancement of refrigeration efficency,and the achievement of the large refrigeration capacity. Finally，the results of our investigations will assist the design and synthesis of the complex materials with "table-like" MCE.

R-Co-Al、R-Ni-Al(R=Gd,Tb,Dy,Ho,Er)等三元合金相图中存在RAl2，RCoAl,RNiAl等多个铁磁性合金相以及由这些合金相构成的双相、三相区。本项目拟通过"原位复合"的方法，使合金在铸态和适当的热处理条件获得包含多个铁磁性合金相的复相结构，进一步通过成分和显微组织优化，利用不同合金相磁有序温度相互邻近的特点，获得具有"桌面型"磁热效应的复相磁致冷材料。通过本项目制备的复合磁致冷材料可以满足液氮温区附近磁制冷机对工质的需求，实现制冷循环回热平衡、提高制冷效率、获得大制冷量。通过本项目的实施，达到指导"桌面型"复相磁热效应材料的设计和相应材料的制备的目的。

磁Ericsson循环要求磁工质在循环过程中保持回热平衡，从而要求磁致冷材料的磁熵变在一定温度范围内保持不变，即平台型磁热效应，以实现高的制冷效率和大的制冷量。研究发现，R-Co-Al、R-Ni-Al(R=Gd,Tb,Dy,Ho,Er)等三元合金相图中存在RAl2, RCoAl, R2Co2Al, RCo2, RNiAl等多个铁磁性合金相以及由这些合金相构成的双相、三相区，有望获得包含多个具有良好磁热效应的铁磁相，从而实现平台型磁热效应。本项目详细研究了Gd-Co-Al，Gd-Ni-Al，Ho-Co-Al等三元合金体系，在建立化合物的成分、结构、磁热效应关系的基础上，成功获得了具有磁熵变平台的磁致冷合金。所开发的平台型磁热效应合金的工作温度在液氮温区附近，0-5T磁场下的最大磁熵变值高达9.1J/kgK，平台宽度51K。复相多晶合金平台型磁热效应的实现为制备适合磁Ericsson循环的磁致冷工质提供了新的方法，推动了磁制冷技术的实用化。