A Comprehensive Characterization of Industrially Manufactured Hard Chrome Platings and of Thermally Sprayed Alternatives

HVOF-sprayed coatings (WC-17Co, WC-10Co-4Cr, Co-28Mo-17Cr-3Si) have been compared with various kinds of industrially manufactured hard chrome coatings (HCC), whose substrate preparation, deposition process, post deposition treatments greatly affect their characteristics. Microstructure, micromechanical properties, tribological behaviour and corrosion resistance (electrochemical polarization tests and Corrodkote test) have been studied. HVOF-sprayed cermets are harder but less tough than HCC, Co-28Mo-17Cr-3Si are less hard than HCC. Splats detachment causes a comparable or higher mass loss in three-body abrasion than HCC coatings. Forming a uniform surface film, cermet coatings definitely overcome HCC in two-body sliding, while Co-28Mo-17Cr-3Si has insufficient hardness to display good sliding wear resistance. HVOF coatings show no passivation in corrosive media but cermets posses more noble corrosion potentials than HCC, and undergo generalized corrosion in HNO₃ and HCl, with similar corrosion current densities (I_C). HCC passivate and resist well in HNO₃ 0.1N, but undergo pitting corrosion in 0.1N HCl. Definitely different E_C and I_C are recorded for various HCC in HCl. HVOF-sprayed cermet coatings show lower I_C in 0.1N HCl solution than several kinds of HCC. No visible damage occurs on HVOF-sprayed coatings after the Corrodkote test, while non de-hydrogenated HCC suffered pitting corrosion.