HDDR as advanced processing method and recycling technology to address the rare-earth resource criticality in high performance Nd2Fe14B magnets production

Since both established applications and emerging green energy and mobility technologies integrate Nd2Fe14B-based magnet components, great research efforts have been directed towards the maximization of their performance and economic reliability. Significant fluctuations on the supply chains within a quasi-monopolistic rare-earth raw materials market intensified the need to maximize cost-efficiency in the large scale production, to explore alternative processes that have the potential to bring optimal balance of cost and performance and to establish efficient scrap magnet recycling technologies. The focus in this article is on the HDDR treatment, put in the wider context of Nd2Fe14B-based magnets production technologies. It is overviewed as processing route for the fabrication of fine grained, highly coercive anisotropic magnets, and also as a scrap magnet recycling method. The grain boundary diffusion processing (GBDP) methods, additional material engineering strategies developed with the aim to enhance the magnetic properties of the Nd2Fe14B HDDR magnets are also reviewed.