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

该项目旨在表征接头区域的微观结构，重点关注微观结构参数的作用，如相，晶粒的形状和尺寸，晶粒取向和晶界结构。采用电子背散射谱分析技术对铝合金搅拌摩擦焊接头的微观组织进行了表征。111取向的晶粒倾向于几乎平行于旋转工具存在，表明在搅拌摩擦焊过程中在旋转销周围发生了严重的剪切变形。这种织构成分与常规工艺（轧制、挤压等）制备的铝合金中的织构成分不同，搅拌摩擦焊接接头组织在高温下不稳定，表现为晶粒的异常长大。搅拌摩擦焊可以在局部区域产生特殊的微观组织，但微观组织中包含着一些重要的信息，可以作为异常晶粒长大的触发效应。采用基于Potts模型的Monte Carlo模拟方法，对搅拌摩擦焊过程中的晶粒异常长大进行了模拟，结果表明，搅拌摩擦焊过程中的晶粒异常长大是由微观组织引起的 关于我们 阐明了在均匀或非均匀温度场下，局部组织参数在单相和双相组织晶粒长大过程中的作用。本研究提出了一些新的算法。晶界迁移是晶粒生长的基本过程，第二相和温度梯度对晶界迁移有很大影响。在第二相粒子存在的区域或温度较低的区域，晶粒生长受到抑制。在局部区域施加陡温场时，晶粒发生了反常生长等择优生长现象。这一结果为微结构控制提供了新的思路，即采用点加热技术将微结构信息编码到多晶材料中，并结合界面反应实现陶瓷-金属的固态扩散连接。采用化学势图的概念描述了氮化硅与钒、铌、钛和铝化钛等金属界面的相序，重点研究了界面微观结构随微观结构参数空间分布的变化。基于本研究的结果，应该指出的是，我们可以控制局部微观结构利用应变，温度和成分的非均匀场。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