中文摘要：

借助X射线衍射仪、透射电镜及显微硬度仪等先进仪器，研究了经超音速微粒轰击（SFPB）形变热处理Ti-6Al-4V合金表面自身纳米化晶粒尺寸演化及纳米化机制。研究结果表明：超音速微粒轰击使Ti-6Al-4V合金表面获得了纳米组织，并发生显著的加工硬化，表面显微硬度比基体硬度提高了1倍多；随着SFPB处理时间的延长，纳米结构层厚度不断增加，晶粒尺寸逐步细化，当SFPB处理30min后晶粒尺寸趋于稳定，在表层形成了晶粒尺寸约为20nm具有随机取向的纳米等轴晶。Ti-6Al-4V合金表面自身纳米化是由于位错运动、孪晶的形成及交割共同作用的结果；在多方向载荷的重复作用下，在塑性变形区产生了大量的由位错线和高密度位错缠结分割的位错胞，并在位错塞集处产生应力集中，进而形成孪晶；孪晶自身相互交割和位错的滑移相互协调，形成了细小的孪晶和胞状组织；晶胞组织转变为细小多边形亚晶；当孪晶尺寸细化到亚纳米级时，位错的滑移起主导作用，最终通过位错的湮灭和重组形成了具有随机取向的等轴状纳米晶粒。

英文摘要：

The mechanism of surface self-nanocrystallization and the evolution of grain size for Ti-6AI-4V alloy were investigated by means of X-ray diffraction （ XRD）, micro-hardness testing, transmission electron microscope （TEM）. The results showed that the nanostructures were obtained by the supersonic fine particles bombarding （ SFPB）, and had obvious working-harden on the surface lay- er of Ti-6Al-4V alloy. To compare with the matrix material, the surface microhardness increased more than one time. The thickness of the nanostructured layer increased with the extension of SFPB treatment time and finally was stabilized when the SFPB treatment time was more than 30 min. The average size of equiaxed nano-crystallites was approximately 20 nm, which exhibited a random crystallo- graphic orientation on the top surface layer. The surface self-nanocrystallization could be attributed to the formation of twins, twin-twin intersection and dislocation slipping. Under the multidirectional loads of repeating actions, a large number of dense dislocations were formed in the plastic deformation area. The stress concentrations were produced in the dislocation accumulation, and then formed twins. Twin-twin self-intersection and dislocation slipping were coordinated, the refined twins and cystiform microstructure were formed. The cystiform microstructures turned into polygonal ultracystal. When the twin crystals size refined to an ultrananometer level, the dislocation slipping occupied the leading role. The random orientation equiaxed nanocrystallites were finally formed by the dislocation annihilation and recombinant.