Contribution of galvanic coupling with TiN, TiAlN, and CrN to the corrosion of steel in neutral and acidic chloride solutions

Abstract

The inherent defective morphology of the physical vapor deposition (PVD) hard coatings limits their corrosion protective ability. We examined the impact of nitride‐based PVD coatings, including TiN, TiAlN, and CrN deposited on inert substrates by cathodic arc PVD method (CA‐PVD), on the galvanic corrosion of carbon steel. Their contribution was evaluated by zero‐resistance ammeter (ZRA) and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl at pH 2 and 6, with and without aeration. The results indicated the prominent role of the coating type and the coupling environment on the generated galvanic currents. Immersion tests for the TiN‐, TiAlN‐, and CrN‐coated steel cross‐sections visually verified these results. The galvanic current contribution was distinct in environments where oxygen reduction is the dominant cathodic reaction. However, the layers' contribution to galvanic corrosion was minimal in deaerated acidic solutions, which is attributed to the high bonding strength of adsorbed intermediates to the coating surfaces.

Improved Corrosion Resistance of Cathodic Arc Evaporated Al0.7cr0.3-Xvxn Coatings in Nacl-Rich Media

“…In a series of 10 Al 0.7 Cr 0.3− x V x N coatings with varying V-contents, ranging from 5.1 to 22.3 at% on the metal sublattice, each raise in the V-fraction lowered the corrosion currents noticeably, and resulted in a positive shift of the respective corrosion potential. Using the Stern-Geary equation together with the assumption that the coating material remains inert throughout the electrochemical experiment (only the steel substrate accounts for the anodic current), an approximation of the coatings' open porosity was made [3]. Appropriately, the approximation revealed a significant decline in the coatings' porosity values, which is a result of the observed grain-refinement due to increasing V-fractions.…”

“…embedded macroparticles, porosity due to highly orientated columnar growth, pin holes, etc.) allow the corrosive medium to travel unhindered to the coating/substrate interface and generate galvanic couples [1][2][3]. Depending on the materials that make up this galvanic cell, coatings may either act as the anodic element (providing sacrificial protection) [4], or act as the cathodic element, in which anodic dissolution and pitting of the substrate material ensues [5].…”

Surface Engineering of Metals: Techniques, Characterizations and Applications

“…Techniques such as surface pretreatments, interlayer materials, and optimized deposition processes have been investigated to enhance the bonding strength between the coating and the substrate [82][83][84]. For example, the use of intermediate layers such as titanium nitride (TiN) or chromium nitride (CrN) has shown improved adhesion, leading to enhanced wear resistance and an extended component lifespan [85][86][87].…”