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A surface ceramic protective film was prepared on Ti-6Al-4V alloy using laser-assisted ultrasonic nanocrystal surface modification technology (LA-UNSM). The uniform ceramic protective film, which was comprised of Al 2 O 3 and small amounts of TiO 2 and TiN, showed very strong adhesion to the substrate. LA-UNSM treatment dramatically increased the dislocation density and atomic diffusion rate by introducing thermomechanical activation energy, which further greatly reduced the energetic barriers of the oxide to nitride nucleation and growth. Due to the formation of a ceramic protective film and a nanocrystalline gradient reinforcement layer on the sample surface, the surface hardness was dramatically enhanced after LA-UNSM treatment. The electrochemical corrosion behavior in simulated seawater and the fretting wear behavior of samples were also investigated. The results revealed the ceramic protective film and gradient nanocrystalline layer introduced by LA-UNSM could substantially reduce the corrosion current density by 83 % and the wear volume by 90 % as compared to control samples. These results show that LA-UNSM effectively promotes the corrosion and wear property of titanium alloy through forming a ceramic protective film. [Display omitted] • A surface ceramic protective layer was rapidly formed through LA-UNSM. • Significant surface hardening was achieved through grain refinement, work-hardening and the formation of the ceramic phase. • The corrosion resistance and fretting wear resistance of Ti-6Al-4V alloy were dramatically improved through LA-UNSM. [ABSTRACT FROM AUTHOR]

The efficacy of peening treatment depends on the plasticity of the target metal. In this study, the effectiveness of high-amplitude short duration pulsed current in improving the peening efficacy was examined in a process called electropulsing-assisted ultrasonic nanocrystal surface modification (EP-UNSM). During the EP-UNSM process, the target metal, i.e., Ti64, is subjected to simultaneous ultrasonic peening and electropulsing. The high energy pulsed current can generate a critical magnetic field that can induce the transition of the radical pairs formed by dislocations and the pinning obstacles from the singlet state to the triplet state. This leads to higher dislocation mobility and thus higher plasticity for more effective peening treatment. The results show that the sample treated with EP-UNSM had a deeper plastically deformed layer than that for samples subjected to UNSM and continuous current–assisted UNSM (CC-UNSM), and the maximum depth of plastic deformation was obtained when using the highest peak current density. Due to microstructure refinement, work hardening, and dynamic strain aging, the EP-UNSM sample had a 50% higher surface hardness compared with the control sample. Moreover, the compressive residual stresses generated by EP-UNSM were higher in magnitude and greater in depth compared to those generated by traditional UNSM. These results demonstrate that pulsed current can effectively improve the peening efficacy and EP-UNSM is an effective method for strengthening Ti64. • Pulsed current leads to higher dislocation mobility and thus higher plasticity for more effective peening treatment. • EP-UNSM generates a gradient nanocrystalline layer in Ti64. • EP-USM results in high surface hardness and higher residual stress magnitude and depth. [ABSTRACT FROM AUTHOR]