Breakdown of the Hall-Petch relationship in extremely fine nanograined body-centered cubic Mo alloys
Breakdown of the Hall-Petch relationship in extremely fine nanograined body-centered cubic Mo alloys
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DOI：
10.1016/j.actamat.2021.116950
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发表时间：
2021-05
期刊：
影响因子：
9.4
通讯作者：
F. Duan;Y. Naunheim;C. Schuh;Y. Li
中科院分区：
文献类型：
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作者：
F. Duan;Y. Naunheim;C. Schuh;Y. Li
面心立方(FCC)金属的力学性能和变形行为已被研究过，但对于体心立方(BCC)金属，这一范围的研究很少。在这里，我们研究了晶粒度从120到4 nm的体心立方Mo(O)合金的硬度和变形行为，涵盖了经典的Hall-Petch行为和标度律破坏的区域，大约在11到4 nm之间。在最强的晶粒度为11 nm时，获得了高达17.3 Gpa的硬度，并且在较小的晶粒度下的断裂与许多行为的变化有关：激活体积的拐点(与形变的速率相关性的变化有关)和更大的剪切局部化。在较粗的颗粒尺寸下，这与晶界的剪切偏移有关，这表明晶间变形(通过滑动或颗粒旋转)越来越普遍。在较细的颗粒尺寸下，局部化与在远大于颗粒尺寸的尺度上形成大的剪切带有关。这些行为表明，在最细的晶粒尺寸下，从晶状变形行为向玻璃状变形行为的交叉，与结构中无序区比例的增加相一致。
Mechanical properties and deformation behavior have been studied in face-centered cubic (fcc) metals with extremely fine grain sizes, even below about 20 nm, but this range is rarely studied in the body-centered cubic (bcc) metals. Here, we study the hardness and deformation behavior of bcc Mo(O) alloys with grain sizes from 120 to 4 nm, covering the range of classical Hall-Petch behavior as well as the regime where that scaling law breaks down, between about 11 and 4 nm. A hardness as high as 17.3 GPa was achieved at the strongest grain size of 11 nm, and the breakdown at smaller grain sizes is associated with a number of changes in behavior: an inflection in activation volume (associated with a change in rate dependence of deformation) and increasing shear localization. At coarser grain sizes this is associated with shear offsets at grain boundaries, pointing to an increasing prevalence of intergranular deformation (by sliding or grain rotation). At finer grain sizes localization is associated with the formation of large shear bands at scales far greater than the grain size. These behaviors are suggestive of a crossover from crystal-like to glass-like deformation behaviors at the finest grain sizes, consistent with the increasing fraction of disordered regions in the structure.