As deformation twins have a profound impact on the plastic flow and mechanical properties of metallic materials, enhancing deformation twinning in face-centered cubic (FCC) metallic materials has long served as a unique microstructure design strategy to attain an extraordinary strength-ductility synergy. Deformation twinning, however, rarely occurs in pure FCC Al and its alloys since its generalized planar fault energies (GPFEs) are almost unaffected by most soluble alloying elements such as Mg, Zn and Cu. Here we successfully tune the GPFEs of a nanocrystalline Al-Mg alloy by alloying with Zr, Fe or Y element, and enable deformation twinning in the Zr-, Fe- and Y-containing alloys. Based on a combined analysis of microscopic observations, modeling and ab initio calculations, we find a strong grain-size-dependent twinning (i.e., twinning occurs in preferable grains having sizes in the range ∼20–40 nm), as well as only one single twinning plane (i.e., twinning occurs in single, parallel atomic planes) for twin formation rather than intersecting twinning planes (i.e., twinning occurs in multiple, unparallel atomic planes) usually observed in coarse-grained FCC materials. This interesting twinning behavior is further observed to be accompanied by grain rotations, producing defective twin boundaries. Our experimental results extend the current understanding of the plastic deformation mechanisms in nanograined metallic materials, and will guide microstructure design of twinnable nanograined Al alloys with an improved strength-ductility synergy.

中文翻译：

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调节广义平面断层能量以实现纳米晶铝合金中的变形孪生


由于变形孪晶对金属材料的塑性流动和机械性能具有深远的影响，因此增强面心立方（FCC）金属材料的变形孪晶长期以来一直作为一种独特的微观结构设计策略，以实现非凡的强度-延展性协同作用。然而，变形孪生很少发生在纯 FCC Al 及其合金中，因为其广义平面断层能 (GPFE) 几乎不受大多数​​可溶合金元素（如 Mg、Zn 和 Cu）的影响。在这里，我们通过与 Zr、Fe 或 Y 元素合金化，成功地调节了纳米晶 Al-Mg 合金的 GPFE，并在含 Zr、Fe 和 Y 的合金中实现了变形孪晶。基于显微观察、建模和从头计算的综合分析，我们发现了一种强烈的晶粒尺寸依赖性孪晶（即，孪晶发生在尺寸范围约为 20-40 nm 的优选晶粒中），并且只有一个通常在粗晶 FCC 材料中观察到，孪晶形成是单孪晶面（即孪晶发生在单个平行原子平面中），而不是相交孪晶面（即孪晶发生在多个不平行原子平面中）。进一步观察到这种有趣的孪生行为伴随着晶粒旋转，产生有缺陷的孪晶界。我们的实验结果扩展了目前对纳米晶金属材料塑性变形机制的理解，并将指导具有改进的强度-延展性协同作用的可孪晶纳米晶铝合金的微观结构设计。