Nanotwinned alloys are of interest due to their high strength and ductility, but twin boundaries may not be stable under shear. Computational studies indicate that high hydrostatic pressure may suppress detwinning mechanisms. Here, we investigate the microstructural changes of nanotwinned-nanocrystalline copper-nickel and Inconel 725 alloys under quasi-hydrostatic pressures up to 50 gigapascals (GPa). The alloys are compressed in a diamond anvil cell. In-situ x-ray diffraction (XRD) and ex-situ transmission electron microscopy (TEM) were employed to monitor microstructural changes. Twin boundary deformation and grain growth occur at 11.4 GPa quasi-hydrostatic pressure in the copper-nickel alloy. Molecular dynamics (MD) simulations reveal that hydrostatic pressure causes elevated local shear stress at grain boundaries, which leads to atomic rearrangements. A superposition of hydrostatic and deviatoric pressures lead to partial dislocation mediated twin boundary migration. In contrast, the Inconel 725 alloy showed stable twin and grain boundaries up to a quasi-hydrostatic pressure of 12.7 GPa. Texture, high solid solution strengthening, and low stacking fault energy are hypothesized to the enhanced microstructural stability in Inconel 725.

中文翻译：

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高压下的纳米孪晶合金


纳米孪晶合金因其高强度和延展性而受到关注，但孪晶界在剪切下可能不稳定。计算研究表明，高静水压力可能会抑制分离机制。在这里，我们研究了纳米孪晶-纳米晶铜镍合金和 Inconel 725 合金在高达 50 吉帕 （GPa） 的准静水压力下的微观结构变化。合金在金刚石砧单元中被压缩。采用原位 X 射线衍射 （XRD） 和非原位透射电子显微镜 （TEM） 监测微观结构变化。铜镍合金的双晶界变形和晶粒生长发生在 11.4 GPa 准静水压力下。分子动力学 （MD） 模拟表明，静水压力会导致晶界处的局部剪切应力升高，从而导致原子重排。静水压力和偏压的叠加导致部分位错介导的孪晶边界迁移。相比之下，Inconel 725 合金在准静水压高达 12.7 GPa 时表现出稳定的孪晶界和晶界。织构、高固溶体强化和低堆叠断层能量被假设为 Inconel 725 微观结构稳定性增强。