Role of Local Microstructure Parameters in the Evolution Process of Interfacial Microstructures of Joints

本项目旨在表征节理区域的微观结构，重点研究相、晶粒形状和尺寸、晶粒取向和晶界结构等微观结构参数的作用。采用电子后向散射分析方法对铝合金搅拌摩擦焊接接头的组织进行了表征。111取向晶粒几乎平行于旋转刀具存在，表明在FSW过程中，旋转销周围发生了严重的剪切变形。这种织构成分不同于通过轧制、挤压等常规工艺加工的铝合金中出现的织构成分。FSW接头在高温下组织不稳定，晶粒生长异常。FSW可以在局部区域产生特殊的微观组织，但微观组织中有一些重要的信息可以作为异常晶粒生长的触发效应。采用基于Potts模型的蒙特卡罗模拟方法，进一步阐明了均匀温度场和非均匀温度场下，局部微观结构参数在单相和双相组织晶粒生长过程中的作用。在本研究中建立了一些新的算法。晶界迁移是晶粒生长的基本过程，晶界迁移受第二相或温度梯度的强烈影响。第二相颗粒存在的区域或温度较低的区域晶粒生长迟缓。在局部区域施加较陡的温度场时，会发生晶粒异常生长等优先生长现象。这一结果为微结构控制提供了新的思路，即利用点加热技术将微结构信息编码到多晶材料中。通过界面反应研究了陶瓷与金属的固态扩散键合。利用化学势图的概念描述了氮化硅与钒、铌、钛、铝化钛等金属界面的相序。目前的研究重点是界面微观结构，这些微观结构随微观结构参数的空间分布而变化。基于本研究的结果，我们应该注意到，我们可以利用应变、温度和成分的非均质场来控制局部微观结构。少

This project aims to characterize microstructure of joint regions focusing on the role of microstructural parameters such as phases, shape and size of grains, grain orientations and grain boundary structures. Electron Back-Scattering Pattern analysis was utilized to characterize microstructures of Aluminum alloy joint fabricated by friction stir welding(FSW). 111 oriented grains tended to exist almost parallel to the rotating tool, indicating a heavy shear deformation is taking place around the rotating pin during FSW. This texture component is different from those appeared in Al alloys fabricated by conventional processing such as rolling, extrusion and so on. The microstructure of FSW joints is unstable at elevated temperature, showing an abnormal grain growth. FSW can produce peculiar microstructure in a localized region but the microstructure has some important information to be acting as a trigger effect of abnormal grain growth.A Monte Carlo simulation based on Potts model was pe … More rformed to elucidate the role of local microstructure parameters in grain growth process of single and dual phase structures under uniform or heterogeneous temperature fields. Some new algorithms were established in the present research. Grain boundary migration, which is an essential and fundamental process for the grain growth, was strongly affected by second phase or temperature gradient. Retardation of grain growth was observed in the region where second phase particles exist or temperature was lower than the other area. Preferential grain growth such as abnormal grain growth was taking place when a steep temperature field was applied in a localized area. This result gave us a new idea for microstructure control, that is spot heating techniques for coding microstructure information into polycrystalline materials.Solid-state diffusion bonding of ceramics to metals was performed concerning the interfacial reaction. A concept of chemical potential diagram was utilized for describing phase sequence in the interfaces between silicon nitride and metals such as vanadium, niobium, titanium and titanium aluminide, and so on.The present project focused on the interfacial microstructures that show wide variety depending on the spatial distributions of microstructure parameters. Based on the findings of the present study, it should be noted that we can control local microstructure utilizing heterogeneous field of strain, temperature and compositions. Less