A nanostructured surface layer was formed on the ends of TA17 bars by means of high energy shot peening (HESP). Microstructures in the plastic deformation layer were systematically characterized and analyzed by using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), microhardness measurement and X-ray diffraction (XRD). Based on the experimental observations and analysis, nanograins with an average size of 35±5 nm were achieved on the top surface layer, the micro-hardness on the top surface is near twice that of the coarse-grained matrix. In terms of special metals materials, the stress and strain rate are critical for grain refinement in the process of surface self-nanocrystal-lization (SSNC). On the basis of discussion for microstructure in the plastic deformation layer, the grain subdivision mechanism of TA17 was drawn that twinning deformation transformed coarse grains into fine twinning lamellae at the low strain rate level, and the submicronic grains are broken down into randomly oriented nanograins by means of dislocation glide at high level of strain.
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