Microstructure and corrosion Properties of WAAM Nickel Alloy 59 and 316L Stainless steel FGM

Wire arc additive manufacturing (WAAM) was used to deposit a functional graded material (FGM) wall consisting of alternating layers of ER316L-Si (316L) and ERNiCrMO-13 (Alloy 59) wires. Investigation of its microstructure using SEM-EDX showed that the microstructure across layers was continuous and homogenous and that iron diffuses greatly into Ni alloy layers. The evaluation of its mechanical properties showed that the ultimate tensile strength is between that of the nickel alloy and stainless steel while the yield strength was reduced. The evaluation of the corrosion properties using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) showed that mixing 316L with Alloy 59 resulted in improved passivity and better corrosion resistance compared to the Alloy 59 wall. In the case of Alloy 59, the rapid solidification characteristic for WAAM results in a high level of secondary phase precipitation rich in Cr and Mo. Thus, the matrix is depleted of those alloying elements, leading to a drop in corrosion resistance. XPS analysis for the passive layer showed that it was composed of two layers: the outer layer was composed of Ni oxides and hydroxides and Cr hydroxides while the inner layer was mostly composed of Cr oxides (Cr₂O₃). This study shows that FGM composed of Alloy 59 and 316L can enhance corrosion resistance by mitigating the effects of chloride ions solution of Alloy 59.