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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]

In this study, an innovative surface treatment method, electropulsing assisted laser shock peening (EP-LSP), was used to process Ti64 samples. In EP-LSP, metallic samples are subjected to simultaneous high strain rate plastic deformation and high-frequency (100–500 Hz) short-duration (100 μs) pulsed electric current. The effects of EP-LSP on surface finish, microstructure, and micro-hardness of Ti64 alloy were investigated and compared with continuous current assisted LSP (CC-LSP) having the same bulk heating effect. It was observed that EP-LSP produced higher surface hardness and deeper hardened layer, both of which indicate greater plastic deformation. Tensile tests were carried out to evaluate the plasticity of Ti64 subjected to pulsed current and continuous current with the same bulk heating effect. It was observed that pulsed current can more effectively decrease the flow stress and thus resulted in greater plasticity in Ti64 compared with continuous current, even though the bulk heating effect was the same. In addition, the higher the peak current density, the more effective the flow stress reduction. As a result, pulsed current can more effectively improve the effectiveness of LSP treatment, as manifested by higher surface hardness and deeper plastic deformation layer. It is believed that an athermal effect in addition to the thermal effect related to pulsed current exists in EP-LSP. • EP-LSP results in higher surface hardness and deeper hardened layer compared with LSP. • Higher peak current density leads to more effective EP-LSP treatment. • Pulsed current is more effective in improving the plasticity of Ti64 compared with continuous current. • An athermal effect that cannot be explained by resistive heating exists in EP-LSP. [ABSTRACT FROM AUTHOR]

Microstructure inhomogeneity is imparted into the surface of a Vit1b Zr-based bulk metallic glass (BMG) using ultrasonic nanocrystal surface modification (UNSM). As a result, compressive residual stresses with a maximum magnitude of 1130 MPa were induced in the near-surface region. Substantial improvements in both fracture strain and strength were observed for the treated specimen in three-point bending tests. The microstructure inhomogeneity and free volume generated by severe plastic deformation resulted in increased shear band density during three-point bending tests, which is evidenced by the vein-like pattern observed on the fracture surface of the treated specimen. Moreover, the enrichment of shear bands can cause the interaction between shear bands and can thus obstruct their propagation, leading to work-hardening behavior. High magnitude compressive residual stresses are also believed to impede and slow down the propagation of the shear bands. The synergistic effect of induced inhomogeneity, increased free volume and compressive residual stresses improves the fracture stress and strain of the UNSM-treated BMG. [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]