Femtosecond laser rejuvenation of nanocrystalline metals
Femtosecond laser rejuvenation of nanocrystalline metals
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DOI：
10.1016/j.actamat.2018.06.027
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发表时间：
2018-09
期刊：
影响因子：
9.4
通讯作者：
G. Balbus;M. Echlin;Charlette M. Grigorian;T. Rupert;T. Pollock;D. Gianola
中科院分区：
文献类型：
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作者：
G. Balbus;M. Echlin;Charlette M. Grigorian;T. Rupert;T. Pollock;D. Gianola
纳米晶金属由于其高浓度的晶界和相应的晶界处的结构无序而不同于传统的工程材料。纳米晶材料中的局部无序效应表现为使人联想到完全非晶材料的方式，例如介观剪切局部化和压力依赖性屈服，这是由于晶界的高浓度及其在控制塑性方面的优势。纳米晶材料中的弛豫过程（诸如低温退火）促进晶界的重新配置并降低其能量，已经显示出增强机械强度。然而，尚未观察到提高纳米晶金属能量的过程，限制了性能的可调性和抑制剪切局部化的前景。在这里，我们使用飞秒激光加工作为一个独特的非平衡过程，可以产生复杂的应力状态，由于超快电子激发和随后的弛豫事件。对纳米晶Al-O和Cu-Zr合金的实验表明，亚烧蚀飞秒激光脉冲导致高达87%的硬度降低，而晶粒尺寸没有变化，这可以归因于晶界介导的过程。我们的研究结果和玻璃体系中的复兴过程之间的平行关系将在通过新的加工路线控制亚稳结构构型的背景下进行讨论。
Nanocrystalline metals are distinct from traditional engineering materials due to their high concentration of grain boundaries and corresponding structural disorder at grain boundaries. The effect of local disorder in nanocrystalline materials manifests in ways reminiscent of fully amorphous materials, such as mesoscale shear localization and pressure-dependent yielding, owing to the high concentration of grain boundaries and their predominance in governing plasticity. Relaxation processes in nanocrystalline materials that facilitate reconfigurations of grain boundaries and lower their energy, such as low temperature annealing, have been shown to enhance mechanical strength. However, processes that raise the energy of a nanocrystalline metal have not been observed, limiting the tunability of properties and the prospect for suppressing shear localization. Here, we use femtosecond laser processing as a unique non-equilibrium process that can generate complex stress states due to ultrafast electronic excitation and subsequent relaxation events. Experiments on nanocrystalline Al-O and Cu-Zr alloys indicate that sub-ablation femtosecond laser pulses cause up to an 87% reduction in hardness with no change in grain size, which can be ascribed to grain boundary-mediated processes. Parallels between our results and rejuvenation processes in glassy systems will be discussed in the context of controlling metastable structural configurations through novel processing routes.