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Characterization of as-deposited and annealed Cr–C alloy coatings produced from a trivalent chromium bath

“…As mentioned by Safonov et al [18], a characteristic feature of these carbides is their effect on decreasing the hydrogen evolution overvoltage as compared with that of chromium. Thus, chromium carbides in a Cr-C alloy deposit behave cathodic, enhancing corrosion resistance of the coating by shifting of the corrosion potential toward the positive direction [18]. However, the formation of micro-cells between the chromium carbide particles and bulk chromium coating during the anodic polarization could prevent the passive film formation.…”

“…Generally, the good corrosion resistance of a pure Cr coating is due to its passivation as exposed to the corrosive environment [15]. As mentioned in the literature [11,18], the potentiodynamic polarization curves of the conventional Cr coatings in H 2 SO 4 solution follows typical form of active-passive-transpassive anodic behaviour. However, regarding the polarization curves of Cr-C alloy coatings produced in trivalent chromium baths, cathodic portion of the curve, corresponding to hydrogen evolution, is displaced in the anodic direction.…”

“…However, regarding the polarization curves of Cr-C alloy coatings produced in trivalent chromium baths, cathodic portion of the curve, corresponding to hydrogen evolution, is displaced in the anodic direction. As a result, the corrosion potential becomes considerably more positive and locates in the passivity range of chromium [11,18]. Hence, no active region can be observed on Tafel polarization readings of Cr-C alloy coatings.…”

“…These characteristics provide more electrochemical stability and also more compactness of the passive film. It has also been reported that during the anodic polarization, hydrogen absorbed during the Cr-C electrodeposition is released [18]. As a result, a high internal tensile stress releases and causes cracking of the coating and passive film during the anodic polarization [18].…”

“…It has also been reported that during the anodic polarization, hydrogen absorbed during the Cr-C electrodeposition is released [18]. As a result, a high internal tensile stress releases and causes cracking of the coating and passive film during the anodic polarization [18]. It is considerable that the coating deposited at lower pH (0.5) should contain more absorbed hydrogen and thus being more prone to the cracking.…”