Al-Cu合金中纳米层片结构的制备原理及其强化行为

Low strength and poor structural stability, including thermal stability and mechanical stability, are two main concerns for the development of advanced Al alloys, and for extending their application fields. Inspired by our previous work in Ni where the nanolaminated structure was found to be both ultrahard and ultrastable, we aim to introduce high density low angle grain boundaries with lower energy into large grains in a single phase Al-Cu binary alloy, thus refining grains into nano-sized laminates and achieving ultrahigh strength. In this study, we will firstly systematically investigate the structural evolution and the formation mechanisms of nanolaminated structure during plastic deformation, and reveal the key parameters that dominate the structural refinement beyond limit. Based on the quantitative characterization of the nanolaminated structure, the influence of structural size, misorientation angle and micro-texture on structural stability and mechanical strength will be evaluated. Finally, we will theoretically study the interactions between nano-sized lamellar boundaries and dislocations, and the deformation mechanisms and strengthening behavior of nanolaminated structure should be explored. In contrast to the traditional strengthening method (i.e., alloying and age hardening) used in Al alloys, we propose that a better understanding of strengthening from structural refinement by means of low energy nano-sized laminates can enable significant improvement in mechanical strength, which may provide a new strategy for the design of high strength Al alloys.

铝合金强度低和结构稳定性（包括热稳定性和机械稳定性）差是当前发展新型高强铝合金，拓展其应用领域所面临的两大挑战。基于前期工作中发现二维纳米层片结构兼具超高硬度和高热稳定性的现象，本项目拟选用具有高层错能的Al-Cu单相合金为研究对象，通过在晶粒内引入高密度低能小角晶界，获得稳定的纳米层片结构，实现铝合金的显著强化。本项目通过对纳米层片制备技术和原理的系统性研究，揭示纳米层片结构形成的关键性参数及其结构演化的一般规律；通过对纳米层片结构的定量化表征，阐明结构尺寸、界面取向差和显微织构等参数与合金稳定性和强度的关系，进一步深入研究纳米尺度平直界面对位错运动的阻碍与交互作用，揭示纳米层片结构的变形机制与强化行为。不同于铝合金中常见的强化方式（合金化+时效处理），本项目基于纳米尺度层片结构显著的界面强化效应，提出一种新的设计理念，将为高强铝合金的发展与应用研究提供新的途径。

本项目着眼于铝合金强度低和结构稳定性差等制约高性能铝合金发展的基础科学问题，利用自主开发的低温表面纳米化技术，在纯铝和Al-Cu单相合金中引入低能界面，制备出稳定的纳米层片结构，为基于纳米尺度界面调控提高金属材料性能提供了一种新的研究思路。所取得的主要研究结果为：（1）创新性地提出了利用低能小角晶界来稳定纳米结构，在纯铝中制备出纳米层片小角晶界结构，小角晶界比例高达65%，层片厚度为68nm，突破传统晶粒细化极限，并提出了基于小角晶界结构细化与强化的一般规律；（2）自行搭建了一套超低温大塑性变形装置，利用高应变速率、大应变梯度的表面机械碾磨处理技术，在Al-Cu合金中制备出大角晶界主导的纳米层片结构（尺寸为28 nm），其显微硬度高达2.57 GPa。基于球差校正透射电子显微学分析，首次发现超低温塑性变形诱导溶质原子界面偏聚的效应，提出位错滑移诱导溶质原子动态偏聚是一种稳定纳米结构的新机制，为发展新型高强纳米结构铝合金开辟了一个新的途径。这两项研究成果均发表在《Acta Materialia》国际学术期刊上，申请发明专利1项。