Multi-element synergetic grain boundary diffusion:current status and development
Development of aerospace,renewable energy,rail transportation,and other fields has created an urgent demand for high-performance Nd-Fe-B permanent magnets with superior temperature stability.The reliance of high-performance magnets on strategic heavy rare earths(Dy and Tb)has led to an imbalance in the application of rare earth resources in China.Grain boundary diffusion(GBD)technology,which significantly enhances coercivity by forming heavy rare earth shells on grain surfaces,is currently the most efficient technique for utilizing heavy rare earths.In recent years,it has attracted widespread attention and extensive industrial adoption worldwide.Howev-er,the industry predominantly employs pure heavy rare earths as diffusion sources,resulting in challenges such as heavy rare earth accumulation on the surface,shallow diffusion depths,and low utilization efficiency.Based on the latest international progress and the research of our group,this paper discusses the metallurgical behavior and diffu-sion characteristics of different elements in Nd-Fe-B magnets.It proposes a novel approach of partially substituting heavy rare earths with light rare earths and non-rare earth elements to create alloy-based diffusion sources.Through the synergistic effects of multiple elements,localized heavy rare earth shell formation can be achieved,significantly improving diffusion efficiency and reducing costs.The effects of different elements on the coercivity,temperature stability,mechanical properties,and corrosion resistance of magnets during the diffusion process are also elabora-ted.Finally,the future development directions in this field are outlined.
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