Stabilized nanograin boundaries in nickel-molybdenum alloys result in increased hardness with decreasing grain size. Nanograined metals avoid going soft The Hall-Petch relationship links a metal's increasing hardness with decreasing grain size, but it breaks down when grains become very small. This is unfortunate because nanograined metals could otherwise be extremely hard. Hu et al. found a way to circumvent this problem in a set of nickel-molybdenum alloys. They altered the molybdenum composition and annealed the samples at just the right temperature, which stabilized the grain boundaries in their nanograined samples. This allowed hardness to keep increasing with decreasing grain size, which could provide a route for designing superhard coatings. Science, this issue p. 1292 Conventional metals become harder with decreasing grain sizes, following the classical Hall-Petch relationship. However, this relationship fails and softening occurs at some grain sizes in the nanometer regime for some alloys. In this study, we discovered that plastic deformation mechanism of extremely fine nanograined metals and their hardness are adjustable through tailoring grain boundary (GB) stability. The electrodeposited nanograined nickel-molybdenum (Ni–Mo) samples become softened for grain sizes below 10 nanometers because of GB-mediated processes. With GB stabilization through relaxation and Mo segregation, ultrahigh hardness is achieved in the nanograined samples with a plastic deformation mechanism dominated by generation of extended partial dislocations. Grain boundary stability provides an alternative dimension, in addition to grain size, for producing novel nanograined metals with extraordinary properties.

中文翻译：

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晶界稳定性控制极细纳米晶粒金属的硬化和软化

镍钼合金中稳定的纳米晶界导致硬度增加，晶粒尺寸减小。纳米晶粒金属避免变软 Hall-Petch 关系将金属硬度的增加与晶粒尺寸的减小联系起来，但当晶粒变得非常小时它就会分解。这是不幸的，因为否则纳米颗粒金属可能会非常坚硬。胡等人。在一组镍钼合金中找到了规避这个问题的方法。他们改变了钼的成分并在合适的温度下对样品进行了退火，这稳定了纳米晶粒样品中的晶界。这使得硬度随着晶粒尺寸的减小而不断增加，这可以为设计超硬涂层提供一条途径。科学，这个问题 p。1292 常规金属随着晶粒尺寸的减小而变得更硬，遵循经典的 Hall-Petch 关系。然而，对于某些合金，这种关系失效并且在纳米范围内的某些晶粒尺寸处发生软化。在这项研究中，我们发现极细纳米晶粒金属的塑性变形机制及其硬度可以通过调整晶界 (GB) 稳定性来调节。由于 GB 介导的过程，电沉积的纳米晶粒镍钼 (Ni-Mo) 样品在晶粒尺寸低于 10 纳米时变得软化。通过松弛和 Mo 偏析实现 GB 稳定，纳米晶粒样品获得超高硬度，塑性变形机制主要是产生扩展的部分位错。除了晶粒尺寸外，晶界稳定性提供了另一种维度，