Investigation of HVOF-sprayed WC- and NiCr-based coatings to improve corrosion and wear performance of high-strength steel

While electroplated hard chromium (EHC) coatings enhance corrosion resistance and wear strength, it does decrease the fatigue performance of mechanical components due to the existence of tensile stresses and cracking in the coatings. The high-velocity oxy-fuel (HVOF) thermal spray process is a potential alternative coating process with lower impact on the fatigue strength. The present study aimed to investigate the wear and corrosion properties of AISI 4340 steel coated with HVOF-sprayed WC- and NiCr-based coatings of WC-CrC-Ni, Ni–Cr-B-Si-Fe and Ni-20Cr as a substitution for EHC coating. Salt spray and pin-on-disk tests were carried out to evaluate the corrosion and wear resistance of the coatings. From the WC- and NiCr-based coatings evaluated, Ni-20Cr and WC-CrC-C-Ni achieved superior corrosion resistance compared to EHC, but with Ni–Cr-B-Si-Fe having inferior performance to all the compositions and the EHC. The HVOF coating that resulted in the highest wear resistance was Ni-20 Cr, followed by Ni–Cr-B-Si-Fe and WC-CrC-Ni coatings. Both Ni-20 Cr and Ni–Cr-B-Si-Fe had better wear performance than EHC. The wear mechanisms were investigated through energy-dispersive spectroscopy (EDS) and scanning electron microscopy (SEM) techniques. The primary wear mechanism of Ni–Cr-B-Si-Fe, WC-CrC-Ni and Ni-20Cr HVOF thermal-sprayed coatings was found to be adhesive. Regarding the combination of both corrosion and wear performances, the Ni-20Cr HVOF coating was the only one that improved both properties compared to EHC since it reduced the pin/disk volume loss by about 60% and withstood 1000 h in a salt spray environment.