The superhard ReB₂ system is the hardest pure phase diboride synthesized to date. Previously, we have demonstrated the synthesis of nano-ReB₂ and the use of this nanostructured material for texture analysis using high-pressure radial diffraction. Here, we investigate the size dependence of hardness in the nano-ReB₂ system using nanocrystalline ReB₂ with a range of grain sizes (20–60 nm). Using high-pressure X-ray diffraction, we characterize the mechanical properties of these materials, including bulk modulus, lattice strain, yield strength, and texture. In agreement with the Hall–Petch effect, the yield strength increases with decreasing size, with the 20 nm ReB₂ exhibiting a significantly higher yield strength than any of the larger grained materials or bulk ReB₂. Texture analysis on the high pressure diffraction data shows a maximum along the [0001] direction, which indicates that plastic deformation is primarily controlled by the basal slip system. At the highest pressure (55 GPa), the 20 nm ReB₂ shows suppression of other slip systems observed in larger ReB₂ samples, in agreement with its high yield strength. This behavior, likely arises from an increased grain boundary concentration in the smaller nanoparticles. Overall, these results highlight that even superhard materials can be made more mechanically robust using nanoscale grain size effects.

中文翻译：

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二硼化铼纳米晶体尺寸依赖性屈服强度的高压研究

超硬ReB ₂系统是迄今为止合成的最硬的纯相二硼化物。_{之前，我们已经演示了纳米ReB 2}的合成以及使用这种纳米结构材料通过高压径向衍射进行纹理分析。在这里，我们使用一系列晶粒尺寸 (20–60 nm) 的纳米晶 ReB ₂来研究纳米 ReB _{2系统中硬度的尺寸依赖性。}我们利用高压 X 射线衍射来表征这些材料的机械性能，包括体积模量、晶格应变、屈服强度和织构。与 Hall-Petch 效应一致，屈服强度随着尺寸的减小而增加，20 nm ReB _{2表现出比任何较大晶粒材料或块状 ReB 2}显着更高的屈服强度。高压衍射数据的织构分析显示沿[0001]方向的最大值，这表明塑性变形主要由基底滑移系统控制。在最高压力 (55 GPa) 下，20 nm ReB _{2显示出对较大 ReB 2}样品中观察到的其他滑移系统的抑制，这与其高屈服强度相一致。这种行为可能是由于较小纳米粒子的晶界浓度增加所致。总的来说，这些结果表明，利用纳米级晶粒尺寸效应，即使是超硬材料也可以变得更加机械坚固。