Cermet coatings with Fe-based matrix as alternative to WC-CoCr: mechanical and tribological behaviour

Recently, cermet coatings with Fe-based metal matrix have emerged as a less hazardous and more environ- mentally friendly alternative to WC–Co-based ones, which have known inhalation toxicity problems. This study therefore aimed to validate WC-based cermet coatings with Fe-based matrix, obtained using a com- mercially available feedstock powder, as an alternative to WC–CoCr. HVOF-sprayed WC–15 wt.%FeCrAl layers were therefore obtained using different oxygen and fuel (kerosene) flow rates and powder feed rates; their mechanical and tribological properties were compared to HVOF- sprayed WC–10 wt.% Co–4 wt.%Cr. The WC–FeCrAl coatings always exhibited equi-biaxial compressive residual stress state and possessed dense microstructures, with homogeneous metal matrix, but they contained more oxide inclusions than WC–CoCr. Their characteristics were significantly affected by the normalised oxygen-fuel ratio (λ). Small but meaningful differences existed between the ball-on-disc sliding wear rates of the various WC– FeCrAl coatings, the best sample being that with the most favourable combination of compressive residual stress, low oxidation and high hardness/modulus (H/E) ratio. Its sliding wear resistance was comparable to that of WC–CoCr. The cyclic ball impact resistance of WC–FeCrAl layers was also comparable to that of WC–CoCr, but the dry particle abrasion resistance was inferior, because of the brittleness induced by the oxide inclusions.