Corrosion Characteristics of Ni-Based Hardfacing Alloy Deposited on Stainless Steel Substrate by Laser Cladding

In this study, corrosion characteristics of a nickel-based Ni-Mo-Cr-Si hardfacing alloy having 32Mo, 15Cr, and 3Si (wt pct) as alloying elements, deposited on stainless steel SS316L substrate by laser cladding, have been presented. Corrosion behavior of the laser clad layer was evaluated in reducing (0.1 M HCl) and oxidizing (0.5 M HNO₃) environments, in comparison with the reference substrate SS316L, using electrochemical potentiodynamic technique at room temperature. The corrosion mechanisms have been evaluated on the basis of microstructural and microchemical analysis using scanning electron microscopy attached with energy-dispersive spectrometry. Passivity behavior of the laser clad layer was studied in 0.5 M H₂SO₄, using the potentiostatic technique and analyzing the passive layer by X-ray photoelectron spectroscopy. Laser clad layer of Ni-Mo-Cr-Si exhibited higher pitting corrosion resistance in chloride (reducing) environment, indicated by much higher breakdown potential (~0.8 V_SCE) and the absence of pitting as compared to substrate SS316L (~0.3 V_SCE). However, in oxidizing (0.5 M HNO₃) environment, both the laser clad layer and substrate SS316L showed excellent and similar corrosion resistance exhibiting high breakdown potential (~0.85 V_SCE) and wide passivation range (~0.8 V_SCE) with low passive current density (~4 to 7 × 10⁻⁶ A/cm²). The stable passive layer formed on laser clad layer of Ni-Mo-Cr-Si after exposure in 0.5 M H₂SO₄ solution at constant potential ~0.6 V_SCE (within the passive range), consisted oxides of Mo as Mo⁺⁴ (MoO₂) and Mo⁺⁶ (MoO₄)⁻², Cr as Cr³⁺ (mixture of both Cr₂O₃ and Cr (OH)₃), and Si as Si⁴⁺(SiO₂), which have contributed to passivation and repassivation and therefore excellent corrosion behavior.