Wear characteristics of electrolytic hard chrome and thermal sprayed WC–10 Co–4 Cr coatings sliding against Al–Ni–bronze in air at 21 °C and at −40 °C

Hexavalent chromium is carcinogenic and the disposing of solutions for electroplating chromium can create serious health and environmental hazards. Alternative methods of depositing other hard facing materials to replace the chrome hard coating used in aircraft landing gear are being sought and evaluated. One of these is the high-velocity-oxy-fuel (HVOF) thermal sprayed coating of tungsten carbide (WC). Sliding wear tests of HVOF WC–10 Co–4 Cr and electrolytic hard chrome (EHC) coatings sliding against Al–Ni–bronze were performed in a purpose-built multi-site reciprocating test rig in air at room temperature and in an environmental chamber at −40 °C. The effects of several parameters, which included coating thickness, surface finish, sliding velocity and accumulated sliding distance, on the performance of these coatings were studied. The results found that the Al–Ni–bronze sustained higher wear from chrome plated rods than from HVOF coated rods. The Al–Ni–bronze also sustained much higher mass losses at low sliding speed than at high sliding speed. SEM and EDX revealed the existence of a uniformly distributed oxide layer on the Al–Ni–bronze specimens from high-speed tests. The metallographic examination also revealed substantial mass transfer of Al–Ni–bronze to the EHC coating and of tungsten carbide from the HVOF coating to the softer Al–Ni–bronze resulting in the observed weight gain on the EHC specimens and weight loss from the HVOF specimens. Overall, the mass losses of the Al–Ni–bronze were lower at −40 °C than at room temperature and the thickness and surface finish of the coatings as tested appeared to have very little effect on the mass loss of Al–Ni–bronze.