Abnormal grain growth (AGG) is a common phenomenon in liquid-phase sintering of Nd–Fe–B materials. To identify the growth mechanism and suppress AGG, we investigated the grain growth in hydrogenation-disproportionation-desorption-recombination processed Nd–Fe–B strip-cast alloys by field emission scanning electron microscopy and scanning transmission electron microscopy. The Nd₂Fe₁₄B grains grew up normally, and then AGG occurred due to the formation of faceted grains. The Nd₂Fe₁₄B grain that directly contacted with the large liquid triple junction was faceted and presented the maximum driving force (Δg_max) due to its largest grain size. The increase of Nd content and heating temperature induced the occurrence of abnormal Nd₂Fe₁₄B grains and shortened the incubation period of AGG, but within the incubation period, the normal grain growth (NGG) of Nd₂Fe₁₄B grains was promoted. In this work, we proposed an improved mixed control model to analyze the AGG of Nd₂Fe₁₄B grains and presented a two-step heat-treatment process to promote NGG by modifying Δg_max to below the critical driving (Δg_c). The average Nd₂Fe₁₄B grain size of 2.63 μm for NGG was obtained.

中文翻译：

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加氢-歧化-解吸-重组Nd-Fe-B带铸合金的正常和异常晶粒长大

在Nd–Fe–B材料的液相烧结中，异常晶粒生长（AGG）是常见现象。为了确定生长机理并抑制AGG，我们通过场发射扫描电子显微镜和扫描透射电子显微镜研究了氢化-歧化-解吸-重组Nd-Fe-B合金中的晶粒长大。Nd ₂ Fe ₁₄ B晶粒正常长大，然后由于形成多面晶粒而发生了AGG。钕₂的Fe ₁₄乙晶粒直接与大的液体的三结接触被刻面和呈现的最大驱动力（Δ克_最大），因为其最大的晶粒尺寸。Nd含量和加热温度的升高引起Nd ₂ Fe ₁₄ B晶粒异常的出现，缩短了AGG的潜伏期，但在潜伏期内，Nd ₂ Fe ₁₄ B晶粒的正常晶粒长大（NGG）得到促进。在这项工作中，我们提出了一种改进的混合控制模型来分析的Nd AGG ₂的Fe _14个乙晶粒和呈现的两步热处理工艺通过修改Δ促进NGG克_最大到低于临界驱动（Δ克_Ç） 。NGG的平均Nd ₂ Fe ₁₄ B晶粒尺寸为2.63μm。