Enhanced wear and corrosion resistance of the laser direct metal deposited AISI 316L stainless steel by in-situ interstitial N alloying

To meet the applicability in aggressive environments, the wear and corrosion resistance of additively manufactured 316L stainless steel can be improved by alloying with N. In this work, the in-situ interstitial N alloying of 316L with varying amount of CrxN is first manufactured at ambient environment utilizing the rapid cooling character of laser direct metal deposition (DMD). Combined effects of CrxN addition and DMD processing parameters on the relative density, dissolved N content, microstructure, microhardness, wear performance and corrosion behavior are systematically investigated. The results show that the relative density of the DMD 316L decreases with increasing additive amount of CrxN. A full density 316L sample with a high N content of 0.5 wt% is obtained. The N alloying transforms the solidification mode of DMD 316L from "AF" to "A", resulting in a fully austenitic phase. The interstitial N promotes the formation of planar dislocations, nano-stacking faults and nano-twins during DMD. As the CrxN addition increases, both the microhardness (278-312 HV) and wear resistance are significantly enhanced owing to the dislocation strengthening and interstitial N solid solution strengthening. Compared with CrxN-free DMD 316L, the DMD 316L with CrxN addition presents superior pitting corrosion resistance. The increasing CrxN addition progressively improves the pitting corrosion resistance due to the positively synergistic effect Cr-N on the stability and repassivation ability of the passive film. This work provides a practical and cost-effective approach for manufacturing advanced 316L with exceptional properties.