Effects of ultrasonic surface rolling process on microstructure and corrosion behavior of TC4 manufactured by selective electron beam melting

In this study, TC4 alloy manufactured by selective electron beam melting (SEBM) was subjected to ultrasonic surface rolling processing (USRP). The effects of USRP on the surface and microstructure of the alloy were investigated using optical microscopy, X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and other techniques. The corrosion behavior was analyzed through electrochemical testing methods. The results indicate that USRP causes severe plastic deformation on the surface of SEBM-TC4 alloy, leading to grain refinement, facilitating the formation of a gradient deformation layer (~30 μm thick), and ultimately enhancing surface finish and densification. In 3.5 wt.% NaCl solution, the corrosion potential of the USRP-treated sample (-0.092 VSCE) was significantly higher than that of the sandpaper-ground sample (-0.216 VSCE), and its corrosion current density decreased by approximately 43.5%. Moreover, the passivation film on USRP-treated SEBM-TC4 exhibited a double-layer structure, with TiO2 in the outer layer and (TiO + Ti2O3) in the inner layer. In summary, USRP improves the surface finish and densification of the metal, introduces high-density dislocations in the deformation layer to refine grains, and promotes the formation of a dense passivation film, notably improving the corrosion resistance of SEBM-TC4 alloy.