Enhancing the magnetocaloric response of high-entropy metallic-glass by microstructural control

Abstract

Non-equiatomic high-entropy alloys (HEAs), the second-generation multi-phase HEAs, have been recently reported with outstanding properties that surpass the typical limits of conventional alloys and/or the first-generation equiatomic single-phase HEAs. For magnetocaloric HEAs, non-equiatomic (Gd36Tb20Co20Al24)100−xFex microwires, with Curie temperatures up to 108 K, overcome the typical low temperature limit of rare-earth-containing HEAs (which typically concentrate lower than around 60 K). For alloys with x = 2 and 3, they possess some nanocrystals, though very minor, which offers a widening in the Curie temperature distribution. In this work, we further optimize the magnetocaloric responses of x = 3 microwires by microstructural control using the current annealing technique. With this processing method, the precipitation of nanocrystals within the amorphous matrix leads to a phase compositional difference in the microwires. The multi-phase character leads to challenges in rescaling the magnetocaloric curves, which is overcome by using two reference temperatures during the scaling procedure. The phase composition difference increases with increasing current density, whereby within a certain range, the working temperature span broadens and simultaneously offers relative cooling power values that are at least 2-fold larger than many reported conventional magnetocaloric alloys, both single amorphous phase or multi-phase character (amorphous and nanocrystalline). Among the amorphous rare-earth-containing HEAs, our work increases the working temperature beyond the typical <60 K limit while maintaining a comparable magnetocaloric effect. This demonstrates that microstructural control is a feasible way, in addition to appropriate compositional design selection, to optimize the magnetocaloric effect of HEAs.

第二代高熵合金(非等原子比)具备超越传统合金和第一代等原 子比单相高熵合金性能限制的优异性能. 对于磁热高熵合金, 非等原子 比(Gd36Tb20Co20Al24)100−xFex纤维的居里温度最高达108 K, 这克服了含 稀土高熵合金低温(即普遍工作温区在60 K以下)的限制. x = 2和3合金 含有微量纳米晶, 这使得合金具有宽化的居里温度分布. 本文使用电流 退火技术, 通过对微观结构调控进一步优化x = 3纤维的磁热性能. 电流 退火使纤维非晶基体沉淀析出纳米晶, 并造成两相间成分的差异. 缩放 过程中使用两个参考温度, 克服多相特征所造成的缩放磁热曲线的困 难. 两相成分差异随着电流密度的增加而增大, 在一定限度内, 成分差 异扩大纤维工作温区, 同时使相对制冷能力提升至许多传统磁热合金 (无论是单非晶相还是多相(非晶和纳米晶))的2倍以上. 相比于其他含 稀土高熵非晶合金, 本项工作显示出在温度限制(60 K)之上较好的磁热 性能. 这揭示了除适当的成分设计外, 微观结构调控是优化高熵合金磁 热性能的可行方法.