Microstructure evolution and enhanced corrosion resistance of additively manufactured 316L/18Ni300 multi-material parts by process optimization and heat treatment

Additive manufacturing enables easier fabrication of multi-material components, where the interface quality and corrosion resistance are critical factors influencing subsequent applications. This study systematically investigates the microstructure evolution and corrosion behaviour of 316L/18Ni300 multi-material fabricated by laser powder bed fusion. Both process parameters and heat treatment are conducted to improve the bonding quality and corrosion resistance. The poor surface finish of the pre-printed 316L layer and the mismatch in physicochemical properties between the materials caused interface defects, reducing the interfacial corrosion resistance. Remelting the interface once reduced the porosity from 0.5% to 0.17%. Corrosion in the 316L/18Ni300 system was primarily driven by heterogeneous microstructural and elemental distributions at the interface, along with corrosion potential differences between the dissimilar materials. Localized corrosion occurred in high-martensite regions, lowering overall corrosion resistance compared to single-material parts. Solution treatment enhanced the uniformity of grain size and elemental distribution at the interface and within the marageing steel, thereby reducing the corrosion current density (Icorr) from 10.5 ± 3.2 μA/cm 2 to 4.28 ± 1.96 μA/cm 2 . Nevertheless, both direct aging (DAT) and solution aging treatments (SAT) augmented the austenite - martensite interface and nanoscale precipitates, resulting in elevated Icorr of 13.4 ± 2.71 μA/cm 2 for DAT samples and 16.5 ± 1.96 μA/cm 2 for SAT samples, respectively. Concurrently, aging treatments increased the interface microhardness to approximately 450 HV, well above that of 316L stainless steel (approximately 200 HV). This study provides effective strategies to enhance the corrosion resistance of additively manufactured multi-material, promoting their safe and economical applications.