High-pressure strengthening in ultrafine-grained metals
High-pressure strengthening in ultrafine-grained metals
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DOI：
10.1038/s41586-020-2036-z
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发表时间：
2020-02
期刊：
影响因子：
64.8
通讯作者：
Xiaoling Zhou;Z. Feng;Linli Zhu;Jianing Xu;L. Miyagi;Hongliang Dong;H. Sheng;Yanju Wang;
中科院分区：
文献类型：
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作者：
Xiaoling Zhou;Z. Feng;Linli Zhu;Jianing Xu;L. Miyagi;Hongliang Dong;H. Sheng;Yanju Wang;
根据Hall-Petch关系，金属的强度随着晶粒尺寸的减小而增加，据报道，在约10至15纳米的临界晶粒尺寸处破裂。随着晶粒尺寸减小超过该点，变形的主要机制从位错介导的过程切换到晶界滑动，导致材料软化。在一种先前的方法中，通过弛豫和钼偏析来稳定晶界，以防止晶粒尺寸低于10纳米的镍-钼合金中的这种软化效应。在这里，我们跟踪在原位的屈服应力和变形织构的纯镍样品的各种平均晶粒尺寸使用金刚石对顶砧单元加上径向X射线衍射。我们的高压实验揭示了晶粒尺寸从200纳米到3纳米的样品的连续强化，在晶粒尺寸小于20纳米时强化增强（而不是减少）。我们在3纳米晶粒尺寸的样品中实现了约4.2吉帕斯卡的屈服强度，比商业镍材料强十倍。在这里研究的压力范围内，在晶粒尺寸为3纳米的镍中获得了10.2吉帕斯卡的最大流动应力。我们在金和钯样品中看到了类似的压缩强化模式，直到最小的晶粒尺寸。模拟和透射电子显微镜显示，在晶粒尺寸为3纳米的镍中观察到的高强度是由强化机制的叠加引起的：部分和全部位错硬化加上晶界塑性的抑制。这些见解有助于通过材料工程正在进行的超强金属研究。
The Hall–Petch relationship, according to which the strength of a metal increases as the grain size decreases, has been reported to break down at a critical grain size of around 10 to 15 nanometres,. As the grain size decreases beyond this point, the dominant mechanism of deformation switches from a dislocation-mediated process to grain boundary sliding, leading to material softening. In one previous approach, stabilization of grain boundaries through relaxation and molybdenum segregation was used to prevent this softening effect in nickel–molybdenum alloys with grain sizes below 10 nanometres. Here we track in situ the yield stress and deformation texturing of pure nickel samples of various average grain sizes using a diamond anvil cell coupled with radial X-ray diffraction. Our high-pressure experiments reveal continuous strengthening in samples with grain sizes from 200 nanometres down to 3 nanometres, with the strengthening enhanced (rather than reduced) at grain sizes smaller than 20 nanometres. We achieve a yield strength of approximately 4.2 gigapascals in our 3-nanometre-grain-size samples, ten times stronger than that of a commercial nickel material. A maximum flow stress of 10.2 gigapascals is obtained in nickel of grain size 3 nanometres for the pressure range studied here. We see similar patterns of compression strengthening in gold and palladium samples down to the smallest grain sizes. Simulations and transmission electron microscopy reveal that the high strength observed in nickel of grain size 3 nanometres is caused by the superposition of strengthening mechanisms: both partial and full dislocation hardening plus suppression of grain boundary plasticity. These insights contribute to the ongoing search for ultrastrong metals via materials engineering.