应变局部化破坏热稳定纳米晶粒结构
Disruption of Thermally-Stable Nanoscale Grain Structures by Strain Localization
摘要：
最近已经观察到平均晶粒尺寸仅为几纳米的纳米晶体金属通过形成剪切带而失效。在这里，我们研究了这种现象，在纳米晶镍，其晶粒结构稳定掺杂W，特别侧重于了解如何应变局部化驱动的纳米晶粒结构的演变。剪切带开始与微压缩和纳米压痕实验，然后由特定网站的透射电子显微镜来表征的微观结构。晶粒生长和织构的形成内观察到的剪切带，其中有各种各样的厚度。这些演化的区域具有明确的边缘，这排除了局部温度上升作为可能的形成机制。在远离剪切带的区域没有发现结构演化，即使在发生显著塑性形变的位置也没有发现结构演化，表明仅塑性应变不足以引起演化。相反，需要强烈的应变局部化以在热稳定的纳米晶合金中诱导机械驱动的晶粒生长。
英文摘要：
Nanocrystalline metals with average grain sizes of only a few nanometers have recently been observed to fail through the formation of shear bands. Here, we investigate this phenomenon in nanocrystalline Ni which has had its grain structure stabilized by doping with W, with a specific focus on understanding how strain localization drives evolution of the nanoscale grain structure. Shear banding was initiated with both microcompression and nanoindentation experiments, followed by site-specific transmission electron microscopy to characterize the microstructure. Grain growth and texture formation were observed inside the shear bands, which had a wide variety of thicknesses. These evolved regions have well-defined edges, which rules out local temperature rise as a possible formation mechanism. No structural evolution was found in areas away from the shear bands, even in locations where significant plastic deformation had occurred, showing that plastic strain alone is not enough to cause evolution. Rather, intense strain localization is needed to induce mechanically-driven grain growth in a thermally-stable nanocrystalline alloy.
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