Alternative tribological coatings to electrodeposited hard chromium: a critical review

Abstract

The traditional importance of hard chromium electroplating in surface engineering is recognised and the key features of this well-established technology are summarised. Despite the high hardness, corrosion protection and wear resistance of chromium electrodeposits, a number of alternative coating compositions and application techniques have been developed for specific applications in tribology. Environmental challenges associated with hard chromium electroplating are highlighted and the need to develop and evaluate alternative coatings is stressed. Key examples of the alternative coatings are described, including their method of application, microstructure and tribological performance in controlled service environments. Research needs requiring rapid development are highlighted. A summary is given of the most competitive coatings and those having the potential to match the performance of hard chromium in selected applications are identified.

Recent advances in electroless nickel‑boron coatings

“…Hard chrome is an electrodeposited chromium coating obtained from a bath that is typically used chromic acid as a metal source. In the presence of sulfuric acid, an equilibrium between chromic (III) and dichromic (VI) acid forms, and the dichromic acid is reduced to metallic chromium [207]. However, other technologies based on trivalent chromium are gaining popularity at the lab scale [23,[208][209][210].…”

Electrodeposition of Co-P Coatings Reinforced by MoS2 + Y2O3 Hybrid Ceramic Nanoparticles for Corrosion-Resistant Applications: Influences of Operational Parameters

“…Tafel polarization data are in agreement with the EIS results. The included reinforcing nanoparticles can improve the corrosion performance of the Co-P alloy coatings by different mechanisms as follows: (1) deflecting the path of the corrosion medium, (2) formation of micro-galvanic cells, (3) providing a barrier against the diffusion of corrosive agents, and 4eliminating the present nano-holes and nanovoids. [16,63,64] The reason why the inclusion of 6 g/L nanoparticles into the electrolyte degrades the electrochemical behavior can be ascribed to the agglomeration of the embedded nanoparticles.…”

“…IN recent years, a great desire to find appropriate substitutions for hard chromium coatings has emerged. [1][2][3] Although hard chromium deposits have suitable tribomechanical and corrosion properties, there is a growing demand to diminish their use of because of their harmful effects on human and environmental health. This originates from the release of hexavalent chromium ions (Cr 6+ ), which are toxic and may cause lung cancer in humans during the electrodeposition procedure.…”

Effects of SiC particles codeposition and ultrasound agitation on the electrocrystallisation of nickel-based composite coatings

“…electric current, bath chemistry, and cell geometry, particles load. In choosing the composite, metals with high corrosion resistance, such as nickel or nickel alloys, are desired as the matrix material, whereas hard particles are opted as the reinforcer phase, enhancing the composites' wear resistance [3,4].…”