Enhanced corrosion resistance of laser additive manufactured 316L stainless steel by ultrasonic surface rolling process

The ultrasonic surface rolling process (USRP) was adopted to strengthen the surface corrosion resistance of laser additive manufactured 316L stainless steel (LAMed 316L), and the strengthening mechanism of USRP on corrosion resistance was studied with various static pressures. The surface integrity and corrosion behaviors of LAMed 316L were analyzed by the tests of surface roughness, microhardness, residual stress, electron backscatter diffraction (EBSD), Xray diffraction (XRD), potentiodynamic polarization, electrochemical impedance spectros-copy (EIS), Mott-Schottky (M-S), Xray photoelectron spectroscopy (XPS), and three-dimensional microscope, respectively. The results indicated that the LAMed 316L after USRP obtained the reduced surface roughness up to 95 %, the improved microhardness up to 53 %, the introduced residual compressive stress up to-212 MPa, and the decreased grain diameter about 16 %. The LAMed 316L treated by USRP under the static pressure of 200 N presented the supreme corrosion resistance with the corrosion current density decreased up to 41 %, the po-larization resistance increased up to 34 %, and the donor and acceptor densities reduced about 51 % and 81 %, respectively. The corrosion resistance of LAMed 316L was strengthened by USRP, benefiting from the modified surface roughness, grain refinement, increased Cr2O3 content in the passive film, work hardening, and residual compressive stress.