含有长周期堆垛结构镁合金变形机制的原子尺度研究

Magnesium alloys containing the long period stacking ordered (LPSO) phase has been the focus of much attention, due to their good combination of strength and ductility. However, the mechanism of interaction between deformation twins and LPSO structures or stacking faults (SFs) at the atomic level is not yet clarified very well, and the effect of dislocation movement on the redistribution of elements during intermediate plastic deformation is rarely uncovered, which are the key question for understanding the deformation behavior of Mg alloys as well as designing of Mg alloy with high performance. Mg97Zn1Y2(at%) alloy would be deformed through tension or compression under different temperatures and various strain rates to get unique microstructures. At the atomic level, we will systematically analyze the interaction between SFs enriched with Zn/Y elements or LPSO structures with different long to thickness ratio and deformation twin variants using transmission electron microscopy (TEM) and high resolution scanning transmission microscopy (HRSTEM), then deduce the mechanism and effects of basal precipitates on the nucleation and propagation of different kinds of deformation twins. Meanwhile, the distribution of Mg/Zn/Y elements near the kink boundaries will be investigated by HRSTEM and some other methods associated with TEM, and we will explain the roles of dislocations motion playing on the redistribution of elements during plastic deformation. Our finding would provide theoretical direction of optimizing mechanical properties of magnesium alloys, and advance our understanding of the relationship between dislocation and redistribution of elements in materials during plastic deformation.

本项目立项宗旨是揭示含长周期有序堆垛(LPSO)结构的镁合金，在不同变形条件下LPSO结构与变形孪晶交互作用，以及位错诱发元素再分布现象的微观机理。以含有不同分布及密度的LPSO结构的Mg97Zn1Y2(at%)合金为研究对象，通过不同温度和应变速率的拉伸、压缩等测量其力学性能，采用透射电镜(TEM)和扫描透射电镜(STEM)从原子尺度系统分析富集溶质元素的层错(SF)和LPSO结构与变形孪晶的交互作用，揭示镁合金中不同类型孪晶与沿基面析出强化相之间交互作用的机制，总结交互作用对力学性能的影响规律，为该合金的优化设计提供实验依据和理论基础。同时，采用高分辨扫描透射(HRSTEM)技术结合图像分析，研究LPSO结构扭折(Kink)界面处元素分布特征，揭示LPSO结构中位错运动与其成分变化之间的联系，加深对位错运动诱发元素再分布的认识。

镁合金具有低密度、高比强度和高比刚度等优点，在航空航天、交通运输、3C电子等领域具有广阔的应用前景。深入理解镁合金的变形微观结构特征是其广泛应用的重要前提之一。本项目以含有长周期堆垛有序(LPSO)结构的镁合金为主要研究对象，以先进的像差校正电子显微学为主要研究方法，在原子尺度系统解析镁合金的变形微观结构特征，包括其原子构型及化学特性，并推断其变形机理及对性能的重要影响。取得的重要成果如下：. 1．镁合金的LPSO结构和富集溶质元素的层错(SF)与不同类型形变孪晶均有强烈的交互作用，LPSO/SF将对形变孪晶的萌生和扩展起到一定的阻碍作用，进而影响其力学性能。LPSO结构和特征层错使孪晶偏离孪晶面，孪晶界产生严重晶格畸变；由LPSO片段构成的孪晶界面上分布周期性失配位错，导致LPSO结构中元素发生空间再分布。这些研究为镁合金微观结构设计、调控、变形方式提供了结构基础。. 2．塑性变形导致LPSO结构扭折界面发生溶质元素再分布，且不同变形温度对界面处偏聚元素的原子构型和化学成分都有影响，这将显著影响镁合金的力学性能以及使役行为。室温变形后Mg-Zn-Y合金中Zn元素偏聚于对称扭折界面，呈无规则、团簇或有序分布；热挤压Mg-Zn-Y-Zr合金中Zn、Y和Zr元素在低角度扭折界面上富集，且倾向于重新形成纳米宽度的LPSO片段；热压缩Mg-Co-Y合金中Y元素在基面和非基面的位错处析出，形成了纳米颗粒。镁合金中原子尺度溶质元素的再分布源于位错的萌生、运动和沿位错加速的扩散。这些原子尺度的实验结果为深入探讨塑性形变过程中位错对溶质元素再分布、第二相稳定性的影响增添了新认识。. 目前，相关研究结果已整理总结，在Acta Materialia、Scientific Reports、Scripta Materialia等国际学术期刊上发表论文7篇，另有2篇在审，参加学术会议6次。