机械孪晶强韧化微观力学机制的原位实验研究

Mechanical twinning induced strengthening and toughening (MTIST), which is different from the growth twinning induced strengthening and toughening, is the key technique to enhance the strength and toughness of materials. Based on MTIST the strength of 800 MPa and 60~80% plasticity could be obtained in copper alloys and steels. It plays an important role in developing key engineering materials with high strength and high toughness. In this study, major attention will be focused on MTIST. Systematic tilt and in-situ deformation in high resolution transmission electron microscopy will be adopted as main experiment method. The evolution of dislocation and mechanical twin will be investigated, and the way for mechanical twin baffling dislocation will be analyzed. The mechanism of mechanical twin formation and strengthening would be established. The dislocation elastic mechanics and molecular dynamics simulations will be used to analyze the stress state of mechanical twin and applied stress on dislocation. The microstructure evolution after dislocation interacting with twin boundary will be simulated. By experiments combined with theory analysis, the micromechanics mechanism of mechanical twinning strengthening will be established.

机械孪晶强韧化是与生长孪晶强韧化不相同的另一种有效提高材料强度和韧性的新途径，能使铜合金和钢铁材料达到800~1000 MPa的抗拉强度和20%~60%的延伸率综合力学性能水平，对指导新型结构材料强韧化设计有重要意义。本项目拟以机械孪晶强韧化效应为核心研究内容，以高分辨透射电镜系统倾转和动态原位拉伸为主要实验手段，研究位错与机械孪晶微结构演变，建立机械孪生机制，揭示机械孪晶对位错运动的阻碍方式，构建机械孪晶强化物理模型。以经典位错弹性力学为理论依据，以大规模分子动力学计算为模拟工具，计算机械孪晶应力场及其对位错的应力作用，模拟位错与孪晶交互作用的微结构变化，验证实验所建立的孪生机制和强化模型。最后，通过实验结合理论，阐明机械孪晶强韧化效应的微观力学机制。

机械孪晶强韧化是与生长孪晶强韧化不相同的另一种有效提高材料强度和韧性的新途径，能使铜合金和钢铁材料达到800~1000 MPa 的抗拉强度和20%~60%的延伸率综合力学性能水平，对指导新型结构材料强韧化设计有重要意义。本项目以机械孪晶强韧化效应为核心研究内容，以高分辨透射电镜系统倾转和动态原位拉伸为主要实验手段，系统地研究了面心立方结构的低层错能合金(包括Cu-Al合金和Fe-Mn-Si-Al钢)中机械孪晶的产生和扩展行为，基本阐明孪生位错的产生机制主要为梯锁交滑移，明晰了孪晶的扩展主要通过孪生位错的滑移实现以及孪晶的增厚通过孪生位错的逐层滑移实现，阐明了机械孪晶强韧化效应的关键影响因素是层错能。基于对机械孪生强韧化的深刻理解，利用扭转变形产生孪晶梯度，使孪晶诱发塑性(TWIP)钢屈服强度显著提高且保持塑性不降低，打破了传统的强度与塑性此消彼长的规律，所获得实验结果对于新型金属结构材料的强韧化设计具有一定的指导意义。在本自然基金的资助下，发表了标注本基金资助的学术论文8篇，其中SCI期刊论文7篇，培养研究生4名，申请了2项国家发明专利，取得了较好的研究成果。