Assessment of microstructural and mechanical properties of HVOF sprayed WC-based cermet coatings for a roller cylinder

The present paper concerns an assessment of microstructural and mechanical properties of WC-based cermet coatings for a roller cylinder. With this regard, WC-based coatings were fabricated on NiAl deposited 316 L stainless steel substrates by using HVOF technique. The produced coatings were extensively analyzed with respect to X-ray diffraction (XRD), optical microscopy, image analyzer, scanning electron microscopy (SEM) including energy dispersive spectroscopy (EDS), microhardness and surface roughness. Adhesion strength of the coatings was also measured by using a scratch tester and the scratch was examined with an optical microscope. XRD study revealed that WC, W2C, W, C, Co, CoW9C, Co8W9C, Ni, NiAl, Ni3Al and FeNi phases are present in the coatings. The metallographical observations showed that all coatings had a similar coating microstructure and good contact to the substrate, highly dense structure, low oxide and porosity contents. In addition to structural and microstructural results, microhardness values of WC–Co, WC–Ni, NiAl coatings and stainless steel were measured to be 1700, 1750, 450 and 220 HV, respectively. It was found that the adhesion force value of WC–Co coating (125.9 MPa) is higher than WC–Ni coating (76.2 MPa). In order to determine wear loss, friction coefficient and wear mechanism, wear tests were performed for the WC–Co and WC–Ni coated NiAl deposited stainless steel substrates at 50 and 100 N loads under dry sliding conditions through a pin-on-plate arrangement against AISI 303 L steel counterbody. Regarding wear mechanism of the coatings, the microstructural analysis of worn surfaces was examined by SEM and EDS. It was found that the friction coefficients of WC–Co coating are higher than WC–Ni coating under 50 and 100 N loads at dry sliding conditions. In addition to this, the total wear loss of the WC–Co coating is more than WC–Ni coating on NiAl deposited stainless steel substrates.