Sliding and abrasive wear behaviour of HVOF- and HVAF-sprayed Cr3C2–NiCr hardmetal coatings

This paper provides a comprehensive characterisation of HVOF- and HVAF-sprayed Cr3C2–25wt.% NiCr hardmetal coatings. One commercial powder composition with two different particle size distributions was processed using five HVOF and HVAF thermal spray systems. All coatings contain less Cr3C2 than the feedstock powder, possibly due to the rebound of some Cr3C2-rich particles during high-velocity impact onto the substrate. Dry sand-rubber wheel abrasive wear testing causes both grooving and pull-out of splat fragments. Mass losses depend on inter- and intra-lamellar cohesion, being higher (≥70mg after a wear distance of 5904m) for the coatings deposited with the coarser feedstock powder or with one type of HVAF torch. Sliding wear at room temperature against alumina involves shallower abrasive grooving, small-scale delamination and carbide pull-outs, and it is controlled by intra-lamellar cohesion. The coatings obtained from the fine feedstock powder exhibit the lowest wear rates (≈5x10−6mm3/(Nm)). At 400°C, abrasive grooving dominates the sliding wear behaviour; wear rates increase by one order of magnitude but friction coefficients decrease from ≈0.7 to ≈0.5. The thermal expansion coefficient of the coatings (11.08x10−6°C−1 in the 30–400°C range) is sufficiently close to that of the steel substrate (14.23x10−6°C−1) to avoid macro-cracking. •Particle abrasion involves coarse abrasive grooving and pull-out of coating fragments.•Particle abrasion resistance depends on inter- and intra-lamellar cohesive strength.•Sliding wear at R.T. involves moderate abrasion, carbide pull-out and adhesive wear.•At 400°C, sliding wear rates increase due to more severe abrasive grooving.•Lower friction at 400°C than at R.T. is due to graphite clusters in the wear debris.