纳米晶铝铜合金的离子液体电沉积制备及其结构稳定性研究

Structural instability is one of the fundamental challenges confronted by nanostructured metals, hindering the investigation of its synthesis, intrinsic structural and mechanical properties. Massive grain boundaries in nanomaterials drives up the Gibbs free energy of the system and make nanostructure primarily unstable. Grain boundary energy reduction is the essential way to increase nanostructural stability. It has been recognized that, the nanocrystalline structure can be stabilized via grain boundary segregation of a proper kind of solute atoms, in which case the grain boundary energy can be lowered down. In this program, a low-melting point metal aluminum with copper, an alloying element with strong segregation inclination on the grain boundary of aluminum, will be selected as a modeled material to investigate the effect of grain boundary segregation on nanostructural stability. Nanocrystalline Al-Cu alloys with various grain size and Cu content will be synthesized by electrodeposition in ionic liquids. The evolution of microstructure and composition under heat or plastic deformation will be quantitatively characterized in XRD, TEM and 3D-AP. The dynamics behavior of grain growth and solute segregation will be studied and the mechanism of nanostructural stabilization will be explored as well. This program is aimed at an in-depth understanding of the intrinsic structural and mechanical properties of nanocrystalline metals and providing the theoretical and experimental foundations for strengthening aluminum alloys via nanocrystalline structure formation which is currently unavailable.

结构稳定性差是目前纳米结构金属材料面临的基本问题之一，导致纳米金属材料的制备及本征结构和性能研究难以进行。大量晶界的存在引起系统自由能升高是纳米材料结构稳定性差的根本原因，降低晶界能是提高纳米材料结构稳定性的根本途径。研究表明，适当的合金元素在晶界偏析可以降低晶界能量，使纳米材料在某一晶粒尺寸下保持热力学稳定状态。本项目拟以低熔点金属铝作为模型材料，选择在铝中具有强偏析倾向的铜元素作为合金元素，采用电化学沉积法在离子液体中制备出具有不同晶粒尺寸和合金元素含量的纳米晶Al-Cu合金。通过XRD, TEM和3D-AP等技术对其进行微观结构观察与成分定量表征，研究在热及机械变形作用下Cu原子在晶界偏析的动力学行为，探索晶界偏析对纳米结构的稳定化机理。这项研究将增强对纳米结构金属材料本征结构和性能的认识，为铝的结构纳米化提供理论和实验基础，为强化铝合金提供新的途径。

结构稳定性差是目前纳米结构金属材料面临的基本问题之一，导致纳米金属材料的制备及本征结构和性能研究难以进行。大量晶界的存在引起系统自由能升高是纳米材料结构稳定性差的根本原因，降低晶界能是提高纳米材料结构稳定性的根本途径。本项目利用离子液体电化学沉积法制备纳米结构铝及铝合金，探索纳米结构的形成及稳定化途径。通过研究离子液体中铝的电化学还原规律，控制电结晶的动力学过程，成功制备出纳米晶和纳米孪晶结构的铝样品；利用离子液体电化学方法制备出纳米多孔结构铝并阐明其形成机理；利用有机添加剂成功制备出结构尺寸约4 nm的极小尺寸纳米结构铝样品，通过透射电镜和XRD等结构表征手段发现其具有相似的晶体学取向特征，并且具有高达2.3 GPa的显微硬度。后续热处理出现退火硬化现象，并且在300摄氏度时硬度达到峰值，约2.6 GPa，此时其纳米结构基本不变。利用离子液体制备出铝铜合金和铝铅合金，并研究了合金元素的含量以及在合金中的分布规律。该项研究增强了对纳米结构金属材料本征结构和性能的认识，为铝的结构纳米化和结构稳定化提供了理论和实验依据。