Thickness- and Binder-Chemistry-Dependent Structural, Mechanical, and Tribological Performance of HVOF-Sprayed WC-Co and WC-Co-Cr Coatings on High-Speed Steel

Abstract

High-velocity oxy-fuel (HVOF) spraying was used to deposit WC-Co and WC-Co-Cr coatings on high-speed steel in order to determine how binder chemistry and coating thickness jointly control load support, friction, and dry sliding wear resistance. Nominal 50 and 100 & micro;m coatings were compared within the same substrate framework by XRD, FT-IR, SEM/EDX, cross-sectional image analysis, Vickers hardness testing, dry sliding wear testing, and post-wear SEM/EDX. The coatings retained WC as the dominant crystalline phase, while weak overlapping features were associated with binder-rich regions and limited decarburization products. Cross-sectional observations confirmed continuous coating build-up close to the nominal thicknesses and low apparent dark-feature/porosity fractions. All WC-based coatings increased the effective hardness and reduced mass loss relative to uncoated HSS. Among the tested conditions, WC-Co-Cr-100 provided the highest effective hardness and the lowest mass loss after 1000 m sliding, whereas WC-Co-100 produced the lowest mean coefficient of friction. The results show that low friction and high wear resistance are not governed by identical mechanisms: WC-Co favours interfacial shear reduction, while the thicker Cr-containing coating provides superior resistance to material removal through improved carbide retention, binder stability, and coating-scale load support.