Properties of HVOF-sprayed TiC-FeCrAl coatings

As an alternative to WC-CoCr and Cr3C2-NiCr coatings for wear and corrosion protection, a TiC - 25 vol% (Fe-20 wt%Cr-5 wt%Al) powder, free from hazardous and/or supply-critical elements (Ni, Co, W), was produced by high-energy ball-milling and processed by High Velocity Oxygen-Fuel (HVOF) spraying, obtaining dense ( < 1 vol% porosity), hard (H-IT > 12 GPa) layers with reasonably good deposition efficiency of approximate to 54%. Tribological testing revealed that the TiC-FeCrAl coatings are particularly promising for sliding contacts, as their ball-on-disc wear rates against an Al2O3 counterpart were lower than those of an HVOF-sprayed Cr3C2-NiCr reference, both at room temperature and at 400 degrees C, although they could not match the performance of WC-CoCr. At room temperature, brittle fracture along oxidized lamellar boundaries caused localized spallation, releasing debris in the contact region, but, in the incubation period before spallation cracks could propagate, remarkably low friction (approximate to 0.27) was recorded. At 400 degrees C, spallation was largely suppressed by thermal softening, whilst coarser abrasive grooving became the dominant wear mechanism. TiC-FeCrAl coatings appeared less suited to high-stress abrasion, since extensive brittle fracture resulted in higher wear rates than HVOF-sprayed Cr3C2-NiCr, and to (acidic) corrosive environments. Electrochemical polarisation tests in 0.1 M HCl indeed revealed limited corrosion resistance of the FeCrAl matrix.