Enhanced electrochemical corrosion resistance of 316L stainless steel manufactured by ultrasonic rolling assisted laser directed energy deposition

Under the laser directed energy deposition (LDED) process, the rapid melting and solidification usually lead to the emergence of pores and coarse columnar dendrites, which in turn compromise the properties of the deposited alloys. This study introduced in-situ ultrasonic rolling (UR) as an innovative method to enhance the corrosion resistance of LDED specimens, and the microstructural characteristics and their correlation with corrosion resistance were deeply investigated. The findings reveal that the LDED-UR specimen exhibits a reduction in both the fraction and size of pores. Under the influence of severe plastic deformation generated by LDED-UR process, fully equiaxed grains appear with a reduced average size of 28.61 mu m (compared to 63.98 mu m for the LDED specimen with columnar grains). The electrochemical corrosion resistance of the LDED-UR specimen is significantly enhanced compared to the LDED specimen. This enhanced corrosion resistance can be attributed to the low fraction of small-sized pores, the fine and uniformly distributed Cr-enriched ferrite phase, and the formation of a compact and thick passive film due to dense grain boundaries. The insight of the correlation between microstructure and corrosion behavior opens up a new pathway to enhance the corrosion resistance of LDED specimens.