稀土基非晶合金的低温磁性蓄冷性能研究

The development of efficient low-temperature magnetic regenerator materials is the key to improve the cooling efficiency and performance of small cryocoolers. However, the conventional crystalline magnetic regenerator materials have some inherent drawbacks that limit their application, such as the narrow specific heat peaks, the poor processibility and the high temperature of the specific heat peak. To address these problems, we propose to study potential application of the metallic glasses with wide magnetic transition temperature region, good processing performance and low magnetic transition temperature. The key performance parameters and feasibility of the metallic glasses using as low-temperature magnetic regenerator materials will be investigated. In this project, to explore new rare earth based metallic glasses with excellent low-temperature magnetic regenerator performance, we would change the composition of the existing crystalline alloys by adding some new elements that can improve the glass forming ability. The well-known criteria for glass-forming ability can help in designing the alloy compositions. The water-cooled copper mold casting method will be applied in the fabricating the alloys. The composition, microstructure, magnetic property and the low temperature specific heat of the alloys will be investigated, by which we want to reveal how the component factors, structural factors and magnetic factors affect the low-temperature magnetic regenerator performance of the metallic glasses. The correlations between these properties can further promote optimizing the performance of the low-temperature magnetic regenerator alloys by composition adjustment, heat treatment, and other means. This can provide the preliminary experimental data and the theoretical basis for the further practical application of metallic glasses as low-temperature magnetic regenerator materials.

开发高效的低温磁性蓄冷材料是提高小型低温制冷机制冷效率的关键。而传统晶态磁性蓄冷材料存在比热峰较窄、比热峰温度高、不易于加工成形等问题。针对这些问题，本项目拟将磁转变温区宽、磁转变温度低、加工性能好的非晶合金引入到磁性蓄冷材料领域，考察其作为低温磁性蓄冷材料应用的关键性能参数和可行性。拟在现有晶态低温磁性蓄冷材料的成分基础上，以非晶形成理论为指导，通过添加利于非晶形成的元素，采用水冷铜模铸造法开发新型具有优异低温磁蓄冷性能的稀土基非晶合金。通过考察合金的合金成分、微观结构、磁性能和低温比热，揭示出影响非晶合金低温磁性蓄冷性能的成分因素、结构因素和磁性因素，并建立相互之间的关联性。利用此关联性，通过成分调整、热处理等手段进一步优化合金的低温磁性蓄冷性能。为稀土基非晶合金作为低温磁性蓄冷材料的实际应用，提供初步的实验数据和理论指导。

非晶合金由于具有独特的结构和优异的性能，成为非常具有理论研究和应用价值的功能材料，受到广泛关注。本项目主要研究了稀土基非晶合金的低温蓄冷性能，考察了Cu元素对其蓄冷性能的影响，再者利用熔体抽拉法制备了新型稀土基蓄冷丝材，最后研究了高熵非晶合金的磁热性能。主要结论如下：.蓄冷材料是决定低温制冷机的效率关键因素之一。在前期开发的Tm基非晶合金的基础上，研究了添加Cu元素对Tm基非晶合金的非晶形成能力、磁性能和蓄冷性能的影响。发现，无论用Cu取代Al还是Co，都会降低Tm基非晶合金的非晶形成能力，而对其低温蓄冷性能并没有明显的改善作用。相比于晶态的低温磁性蓄冷材料，非晶合金磁性蓄冷材料的比热峰更宽，能在较宽的温度区间内产生大的低温体积比热。考虑到非晶合金制备方法简便，热稳定性好，抗氧化能力强，因此作为低温磁性蓄冷材料较晶态材料具有更强的稳定性。.如何制备适用于高频脉冲管制冷机的丝网填料是制约其发展的关键难题。我们首次采用熔体抽拉法成功制备了50μm左右表面平整且连续的Er3Ni、(Er3Ni)80Al17Gd3和ErPr等多种合金的蓄冷丝材。Er3Ni蓄冷丝材，既保留了Er3Ni材料的大的低温比热，克服了不锈钢丝网低温比热较低的弱点；又保持了丝状的最优使用外形，减小了流动阻力和轴向导热损失。因此，其蓄冷性能明显优于Er3Ni球和不锈钢丝网。该方法突破了现有稀土基蓄冷材料通过现有拉拔等手段不易加工成丝的技术瓶颈，拥有广阔的应用前景和实用价值。.制备了一系列高熵非晶合金，发现该系列高熵非晶合金都表现出典型的自旋玻璃磁转变特征。该系列高熵高熵非晶合金具有较大的磁熵变、半峰宽和磁制冷能力，HoErTmCoAl高熵非晶合金的磁熵变为14.99 Jkg-1K-1，GdTbDyFeAl高熵非晶合金的半峰宽可以达到116 K，RC为691 Jkg-1，这主要归因于高熵非晶合金的自旋玻璃磁转变行为和复杂的成分结构。该高熵非晶合金不仅具有优异的磁制冷性能，而且通过改变高熵非晶合金的元素种类，可以实现非晶形成能力、磁转变温度、磁熵变和磁制冷能力的大范围调控，是一种具有应用潜力的磁制冷材料。