密排六方金属中纳米尺度晶粒再取向微观机制及力学行为研究

Due to limited number of slip systems in hexagonal close-packed (hcp) metals, the crystal reorientations including twinning, basal/prismatic (BP) transformation and double twinning, are important plastic deformation behaviors, and have close relationship with the strength and ductility of hcp metals. In this project, we focus on study of the micromechanism of nanoscale crystal reorientation and related mechanical behavior. At first, atomistic simulations are applied to investigate the original nucleation and growth of different reoriented crystal at different temperatures and loading conditions, and investigate the influence of crystal reorientation on the slip and other plastic deformation mechanisms. We will specially consider the effect of initial defects and alloy elements on the migration of {10-12} twin boundary and BP interface, and analyze the dislocation mechanism and shuffle mechanism by using the potential energy landscape searching technique at different stress and temperatures. Moreover, based on the study of the double twin and other nanoscale crystal reorientations, the relationship between the migration mechanism of the complex interfaces and the mechanical behavior will be discussed. We will apply this research mainly on magnesium single crystal, and also on other hcp metals. This research will be helpful for understanding the basic theory on strengthening and toughening of hcp metals, and it is important for the optimization design of mechanical properties in hcp metals.

由于密排六方金属可同时启动滑移系数量有限，包含孪晶、基面/柱面（BP）转变、双孪晶等在内的各种晶粒再取向行为是最基本的塑性变形方式之一，与密排六方金属的力学性能和强韧化机理密切相关。本课题以纳米尺度晶粒再取向微观机制和力学行为作为研究对象，首先运用原子模拟方法研究不同载荷和温度条件下纳米尺度再取向晶粒的自然形核和扩展机制，探讨晶粒再取向对滑移等塑性变形行为的影响；考虑初始缺陷及合金元素对{10-12}孪晶界和BP界面迁移机制的影响，并通过引入势能形貌探索方法分析不同应力和温度时界面迁移的位错机制和曳步机制；分析双孪晶和其它纳米尺度晶粒再取向行为，探讨复杂界面形核和迁移的微观机制与密排六方金属力学性能的关系。本研究将基于镁单晶开展，并扩展到其它密排六方金属，是密排六方金属强韧化机制研究的理论基础，对于力学性能的优化设计具有重要意义。

密排六方金属中包含孪晶、基面/柱面（BP）转变、双孪晶等在内的各种晶粒再取向行为是最基本的塑性变形方式之一，与密排六方金属的力学性能和强韧化机理密切相关。本项目主要基于原子尺度模拟方法，研究了密排六方金属中以晶粒再取向为主的塑性变形微观机制及相关力学行为。主要研究成果包括：（1）通过分子动力学模拟，探讨了不同密排六方金属塑性变形的微观机制及温度和应变率效应，表明以基面-柱面转变主导的晶格再取向机制为热激活塑性机制；（2）运用分子动力学和系统势能形貌探索方法研究了拉伸孪晶形核和生长的能量学特征，对于扩展孪晶的形核和生长机制给出了定量的描述；（3）运用分子动力学方法和实验表征，分析了压缩孪晶的孪生位错矢量，并在模拟中发现和分析了一种反常剪切方向的非常规{10-11}孪生机制；（4）运用分子动力学方法研究了类双孪晶、纳米孪晶和分级纳米孪晶的塑性变形机制及强韧化机理，探讨了通过界面微结构调控实现密排六方金属强韧化设计的微观机理。上述研究深入探索了密排六方金属和合金塑性变形的微观机制，对于密排六方金属强韧化设计具有重要的理论和实践意义。