搅拌摩擦加工（FSP）作为一项新型纳米化技术，可成功实现碳钢材料表面纳米化。FSP纳米化受热激活和变形激活协同作用，晶界特征对纳米化形成机制产生显著影响。本项目以碳钢为研究对象，在设计开发FSP表面纳米层制备系统的基础上，通过FSP工具设计、加工参数、强制冷却条件调整等方法制备出不同晶粒尺寸、高角度晶界分数的表面纳米层，采用TEM、SEM、EBSD、AFM等技术对表面纳米层的晶粒尺寸、晶界特征、第二相特征、位错组态等进行分析，掌握表面纳米层的组织演化规律，结合表面纳米结构材料拉伸、疲劳等力学性能参量，获得FSP表面纳米层的微观形成机制，揭示晶界特征、第二相特征和位错运动对纳米层形成机制的影响，阐明表面纳米层的组织稳定性，探讨高比率高角度晶界对材料疲劳性能的作用机理，从而为FSP表层纳米化技术提供基础理论依据。

Surface nanocrystallization of carbon steel can be successfully obtained by friction stir processing (FSP) as a new nanotechnology. Nanocrystallization is integrated controlled by thermal and distortion activation, thus the characteristic of grain boundary has significant effect on nanocrystallization mechanism during FSP. Taking carbon steel as an object, the surface nanocrystalline layer with different grain size and proprotional high-angle grain boundary is fabricated by the modification of FSP tool, processing parameter and forced cooling condition base on the design and fabrication of FSP equipment for nanotechnology. Microstructure evolution of FSP surface nanocrystalline layer is investigated by analyzing the grain size, characteristic of grain boundary and the second phase, and dislocation configuration using TEM, SEM, EBSD and AFM technology. Therefore, Microstructure formation mechanism of FSP surface nanocrystalline layer is obtained by comprehensive analyzing the above microstructure reasearch results and mechanical properties of tensile and fatigue. On the base of above studies, the effect of the characteristic of grain boundary and the second phase and dislocation movement on the formation mechanism of surface nanocrystalline layer is revealed. Microstructure stability and the effect of high ratio high-angle grain boundary on the fatigue property of surface nanocrystalline layer are also interpreted. These results will provide theoretical basis for FSP surface nanotechnology.