多铁性合金的联合制冷效应研究

Solid-state refrigeration based on the caloric effects of ferroic materials has attracted more and more attention since it possesses high cooling efficiency, low energy consuming and none pollution. However, these ferroic materials show large caloric effects only around their phase transition temperatures, which leads to a narrow working temperature region. In order to solve this problem, we put forward an idea of combined caloric effect in this project, i.e., combining the magnetocaloric effect and elastocaloric effect in the multiferroic Ni-Mn based shape memory alloys to extend the refrigeration temperature region. By tuning the composition, substituting other elements and using directional solidification/high-magnetic-field solidification techniques, some multiferroic alloys with large low-field magnetocaloric and elastocaloric effects will be prepared. By studying these alloys, we will investigate the optimal research project for realizing the combined caloric refrigeration and give a deep insight in the mechanism of ferromagnetic-ferroelastic coupling in the multiferroic alloys. This research will provide the experimental basis for realizing the wide refrigeration temperature regions in the Ni-Mn based shape memory alloys.

以铁性材料的制冷效应为基础的固态制冷技术因具有高效率、低能耗和无污染的特点而越来越受到广泛关注。但这些材料一般只在相变点附近表现出大的制冷效应，所以工作温区往往过窄。为了解决这一问题，本项目中我们提出了一种联合制冷的观点，即在同时具有铁磁和铁弹性的多铁性Ni-Mn基铁磁形状记忆合金中，通过联合其磁热效应和弹热效应而达到宽温区制冷的目的。我们将通过合金成分调节、元素替代、定向凝固/强磁场凝固等多种手段制备出在低驱动场下具有大磁热和弹热效应的多铁合金，探讨实现宽温区联合制冷的最佳研究方案，深入研究多铁合金中的铁磁-铁弹耦合机制，为利用Ni-Mn基铁磁形状记忆合金实现宽温区固态制冷提供实验基础。

基于铁性相变的固态制冷技术因环保高效而备受关注。但铁性材料往往只在相变温度附近表现出较大的熵变，导致其制冷温区较窄。为了解决这一问题，我们以同时具有铁磁性和铁弹性的多铁性铁磁形状记忆合金为研究对象，开展了联合制冷效应研究。其主要成果包括：（1）通过成分设计和定向凝固的方式在Ni44Mn46Sn10合金中获得了大的弹热效应；（2）在Ni-Mn-Ga合金中掺杂Ti元素，不但提高了合金的力学性能而且大幅降低了滞后，进而在Ni55Mn18Ga26Ti1合金中获得了具有优良循环特性的大弹热效应；（3）在Ni45Co5Mn37In13合金中通过掺杂Co元素提高了奥氏体的磁矩，获得了大的磁热效应。通过定向凝固等方法，在该合金内获得了大的弹热效应。通过将两个制冷效应联合，获得了从250 K到340 K宽达90 K的制冷温区；（4）我们通过成分调控在Ni43Mn41Co5Sn11合金中获得了室温附近的大磁热和弹热效应，并通过联合两个制冷效应获得了105K的超宽制冷温区。这些研究成果对拓宽相变制冷的工作温区具有重要意义。