Queen Mary, University of London, Mile End Road, London, E1 4NS, UK.
University of Birmingham, Edgbaston, Birmingham, West Midlands, B15 2TT, UK.
Sci Rep. 2017 Sep 11;7(1):11134. doi: 10.1038/s41598-017-11660-9.
In the drive to reduce the critical Heavy Rare Earth (HRE) content of magnets for green technologies, HRE-free Nd-Fe-B has become an attractive option. HRE is added to Nd-Fe-B to enhance the high temperature performance of the magnets. To produce similar high temperature properties without HRE, a crystallographically textured nanoscale grain structure is ideal; and this conventionally requires expensive "die upset" processing routes. Here, a Flash Spark Plasma Sintering (FSPS) process has been applied to a Dy-free NdFeCoGaAlB melt spun powder (MQU-F, neo Magnequench). Rapid sinter-forging of a green compact to near theoretical density was achieved during the 10 s process, and therefore represents a quick and efficient means of producing die-upset Nd-Fe-B material. The microstructure of the FSPS samples was investigated by SEM and TEM imaging, and the observations were used to guide the optimisation of the process. The most optimal sample is compared directly to commercially die-upset forged (MQIII-F) material made from the same MQU-F powder. It is shown that the grain size of the FSPS material is halved in comparison to the MQIII-F material, leading to a 14% increase in coercivity (1438 kA m) and matched remanence (1.16 T) giving a BH of 230 kJ m.
在降低绿色技术中磁铁的关键重稀土（HRE）含量的推动下，无 HRE 的 Nd-Fe-B 已成为一种极具吸引力的选择。HRE 被添加到 Nd-Fe-B 中以提高磁铁的高温性能。为了在不使用 HRE 的情况下获得类似的高温性能，具有结晶织构的纳米级晶粒结构是理想的；而这通常需要昂贵的“模具变形”加工路线。在这里，采用快速闪光火花等离子烧结（FSPS）工艺对无 Dy 的 NdFeCoGaAlB 熔体纺丝粉末（MQU-F，neo Magnequench）进行了处理。在 10 秒的过程中，绿色压坯迅速烧结锻造到接近理论密度，因此代表了一种快速高效的生产模具变形 Nd-Fe-B 材料的方法。通过 SEM 和 TEM 成像研究了 FSPS 样品的微观结构，并利用这些观察结果来指导工艺的优化。将最优化的样品与由相同 MQU-F 粉末制成的商用模具变形锻造（MQIII-F）材料进行直接比较。结果表明，FSPS 材料的晶粒尺寸比 MQIII-F 材料减小了一半，导致矫顽力（1438 kA m）提高了 14%，剩磁（1.16 T）匹配，从而使 BH 提高到 230 kJ m。
