Nd-Fe-B磁体烧结过程晶粒长大行为的研究

定量描述了Nd-Fe-B磁体烧结过程晶粒长大行为，分析了烧结温度、烧结时间、合金粉末粒度及其分布对烧结过程晶粒长大的影响，讨论了烧结过程晶粒长大机制。在Nd-Fe-B磁体烧结过程开始之后的0—1h时间区段，晶粒长大迅速；随着烧结时间的延长，晶粒长大速度减小。合金粉末平均粒度增大，或者合金粉末粒度分布范围增宽，显著促进Nd-Fe-B磁体烧结过程中晶粒的长大。在Nd-Fe-B磁体的烧结过程中，存在两类晶粒长大机制，即Nd2Fe14B颗粒的溶解与析出、Nd2Fe14B颗粒的并合与长大。Nd2Fe14B颗粒的并合与长大不仅使磁体的平均晶粒尺寸增大，也使晶粒尺寸分布范围增宽，是烧结Nd-Fe-B磁体显微组织中出现异常大晶粒的根本原因。

Grain Growth Behavior in Sintered Nd-Fe-B Magnets

The grain growth behavior, the effect of sintering temperature, sintering time, particle size and particle size distribution on the grain growth behavior, and the grain growth mechanism in sintered Nd-Fe-B magnets were investigated. The grain growth progress- es at a much higher rate during the initial 0-1 h sintering time interval and from that onwards the grain growth rate decreases. A larger average particle size or a broader particle size distribution remarkably accelerates the grain growth process, even results in the occurrence of abnormal grain growth. There exist two types of grain growth mechanisms in sintered Nd-Fe-B magnets, i.e., Nd2Fe14B particle dissolution and precipitation, and Nd2Fe14B particle coalescence and growth. It is believed that Nd2Fel4B particle coalescence and growth not only produces a larger average grain size and a broader grain size distribution, but also is the fundamental reason of the formation of abnormally large grains in the microstructure of sintered Nd- Fe-B magnets.