Zhang Wei, Chen Hongyu, Song Xin, Ma Tianyu
College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou 450002, China.
Frontier Institute of Science and Technology, Xi'an Jiaotong University, Xi'an 710054, China.
Materials (Basel). 2021 Sep 9;14(18):5179. doi: 10.3390/ma14185179.
Grain boundaries are thought to be the primary demagnetization sites of precipitate-hardening 2:17-type Sm-Co-Fe-Cu-Zr permanent magnets with a unique cellular nanostructure, leading to a poor squareness factor as well as a much lower than ideal energy product. In this work, we investigated the grain boundary microstructure evolution of a model magnet SmCoFeCuZr (wt. %) during the aging process. The transmission electron microscopy (TEM) investigations showed that the grain boundary region contains undecomposed 2:17H, partially ordered 2:17R, 1:5H nano-precipitates, and a SmCo (n = 2, 1:3R; n = 3, 2:7R; n = 4, 5:19R) phase mixture at the solution-treated state. After short-term aging, further decomposition of 2:17H occurs, characterized by the gradual ordering of 2:17R, the precipitation of the 1:5H phase, and the gradual growth of SmCo compounds. Due to the lack of a defect-aggregated cell boundary near the grain boundary, the 1:5H precipitates are constrained between the 2:17R and the SmCo nano-sheets. When further aging the magnet, the grain boundary 1:5H precipitates transform into SmCo compounds. As the SmCo compounds are magnetically softer than the 1:5H precipitates, the grain boundaries then act as the primary demagnetization sites. Our work adds important insights toward the understanding of the grain boundary effect of 2:17-type Sm-Co-Fe-Cu-Zr magnets.
晶界被认为是具有独特胞状纳米结构的沉淀硬化型2:17型Sm-Co-Fe-Cu-Zr永磁体的主要退磁位点，导致方形度因子较差以及能量积远低于理想值。在这项工作中，我们研究了模型磁体SmCoFeCuZr（重量百分比）在时效过程中的晶界微观结构演变。透射电子显微镜（TEM）研究表明，在固溶处理状态下，晶界区域包含未分解的2:17H、部分有序的2:17R、1:5H纳米沉淀以及SmCo（n = 2，1:3R；n = 3，2:7R；n = 4，5:19R）相混合物。短期时效后，2:17H进一步分解，其特征是2:17R逐渐有序化、1:5H相沉淀以及SmCo化合物逐渐生长。由于晶界附近缺乏缺陷聚集的胞界，1:5H沉淀被限制在2:17R和SmCo纳米片之间。当磁体进一步时效时，晶界1:5H沉淀转变为SmCo化合物。由于SmCo化合物的磁性比1:5H沉淀软，晶界随后成为主要的退磁位点。我们的工作为理解2:17型Sm-Co-Fe-Cu-Zr磁体的晶界效应提供了重要见解。
