Effect of in-situ transverse magnetic field on microstructure, mechanical properties and corrosion resistance of the directed energy deposited 316L stainless steel

A novel in-situ transverse magnetic field (TMF) was first incorporated in the directed energy deposition-arc (DED-Arc) of 316L stainless steel based on cold metal transfer (CMT). As the TMF intensity increased from 0 mT to 20 mT, the morphology of deposited layers became flatter and wider, followed by a decrease in surface waviness from 1.11 mm to 0.69 mm. This is attributed to the enhanced transverse filling and backward widening caused by the forward deflection of the arc and the forward Lorentz force in the molten pool. In addition, the long-columnar dendritic delta-ferrite (4.82 vol%) can be fragmented into short skeletal and granular delta-ferrite (2.64 vol%) in the gamma-austenite matrix, accompanied by the increased fractions of K-S and G-T ' orientation relationships between the gamma and delta phases. The above fragmentation and reduction of delta-ferrite indicate the greater diversity of heat flowing and more sufficient transformation of delta ->gamma under the electromagnetic braking effect and thermoelectric magnetic convection effect, which effectively suppressed Cr-Mo-Ni atomic segregation and inhibited harmful intermetallics precipitation (M23C6 and a) at the gamma-delta interface. X-ray photoelectron spectroscopy and Mott-Schottky plot proved that there are more Cr-Mo-Ni metal oxides and lower oxygen vacancy density in the passive film. Consequently, DED-Arc 316L with 20 mT TMF exhibited higher mechanical properties and corrosion resistance than that with 0 mT TMF. This study provides new insight into real-time modifying the microstructure and improving the service performance of DED-Arc metal parts by in-situ TMF.