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

摘要

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 (similar to 0.8 V-SCE) and the absence of pitting as compared to substrate SS316L (similar to 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 (similar to 0.85 V-SCE) and wide passivation range (similar to 0.8 V-SCE) with low passive current density (similar to 4 to 7 x 10(-6) A/cm(2)). 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 similar to 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. (C) The Minerals, Metals & Materials Society and ASM International 2017