Grain refinement in hafnium (Hf), a typical refractory metal, encounters significant challenges due to its inherent high sintering temperature requirements and uneven sintered capillary force that lead to rapid grain coarsening and inhomogeneity. Herein, we present a novel approach of the pressureless two-step sintering to prepare near-fully dense nanocrystalline Hf with an average grain size of around 40 nm, which represents the smallest grain and highest density for nanocrystalline pure Hf to the date. Such achievements not only broaden the applicability of pressureless two-step sintering but also offer insights to produce large size of finer-grained refractory metals and their alloys.

中文翻译：

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通过无压两步烧结获得近乎完全致密的纳米晶铪


铪 （Hf） 是一种典型的难熔金属，由于其固有的高烧结温度要求和不均匀的烧结毛细管力导致晶粒快速粗化和不均匀，因此在铪 （Hf） 中进行晶粒细化遇到了重大挑战。在此，我们提出了一种无压两步烧结的新方法，以制备平均晶粒尺寸约为 40 nm 的近乎完全致密的纳米晶 Hf，这代表了迄今为止纳米晶纯 Hf 的最小晶粒和最高密度。这些成就不仅拓宽了无压两步烧结的适用性，而且为生产大尺寸细晶粒难熔金属及其合金提供了见解。