Investigation of the role of different grain boundaries in plasticity and microstructure formation during dynamic recrystallization of Mg

本研究的目的是系统地研究不同晶界和晶界三重线对镁合金塑性和动态再结晶的影响。重点讨论在特定晶界存在时的变形和组织发展机制，以及晶界几何、拓扑和晶界网络热力学的影响。为了研究，将使用纯镁和镁合金的双晶、三晶和单晶样品，这些样品将在最近设计的高频感应炉中利用新开发的技术进行专门生长。除了平面应变压缩变形外，还将利用扫描电子显微镜中集成的特殊测试单元进行现场实验。此外，还将测量双晶中不同几何晶界的机械诱导剪切耦合运动。最后，将应用纳米压痕技术来研究镁在各种晶界附近的塑性。从变形和动态再结晶过程中微观组织演变机制的研究中获得的新知识将有助于理解晶界在多晶镁和镁合金变形中的作用。在第一个包中，特殊生长的双晶、三晶和寡晶将通过平面应变压缩变形，然后进行研究，以全面了解各种晶界对镁的塑性和动态再结晶的影响。第二部分包括晶界机械孪生的原位研究，再结晶早期新晶的形成，以及运动位错与晶界/孪晶界的相互作用。在第三个项目工作包中，变形和再结晶行为的研究将扩展到镁-Gd和镁-锌合金的双晶。此外，在第四个工作包中，将测量和综合分析与剪切/塑性变形相关的各种晶界的应力驱动迁移。在本程序的第五个工作包中，将应用纳米压痕技术研究镁在晶界附近的变形行为。

The aim of the proposed research project is to systematically examine the impact of different grain boundaries and grain boundary triple lines on the plasticity and dynamic recrystallization of magnesium. A particular focus will be put on the mechanisms of deformation and microstructure development in the presence of specific grain boundaries, on the influence of the grain boundary geometry, topology and thermodynamics of the grain boundary network. For investigations the bi-, tri- and oligocrystalline samples of pure Mg and Mg alloys will be used, which will be specially grown utilizing newly developed technique in the recently designed high-frequency induction furnace. Besides deformation by plane strain compression also in-situ experiments utilizing the special testing unit integrated in the scanning electron microscope will be performed. Furthermore, the mechanically induced shear-coupled motion of geometrically different grain boundaries in bicrystals will be measured. Finally, the nanoindentation technique will be applied in order to study the plasticity of magnesium in the close vicinity of various grain boundaries. The new knowledge gained from the proposed investigations on the mechanisms of the microstructure evolution during deformation and dynamic recrystallization will make a significant contribution towards an understanding the role of grain boundaries during deformation of polycrystalline magnesium and magnesium alloys.The proposed research program consists of five work packages. In the first package the specially grown bi-, tri- and oligocrystals will be deformed by plane strain compression and subsequently investigated in order to get a comprehensive picture of the impact of various grain boundaries on plasticity and dynamic recrystallization of magnesium. The second package comprises in-situ investigations of mechanical twinning initiated on grain boundaries, the formation of new grains at the early stages of recrystallization and the interaction between moving dislocations and grain/twin boundaries. In the third project work package the investigations on the deformation and recrystallization behavior will be extended to bicrystals of Mg-Gd and Mg-Zn alloys. Also, in the fourth work package stress driven migration of various grain boundaries, associated with a shear/plastic deformation, will be measured and comprehensively analyzed. In the fifth work package of the program the deformation behavior of magnesium in the vicinity of grain boundaries will be investigated in dependence of grain boundary character by applying the technique of nanoindentation.