TiC-NiCr thermal spray coatings as an alternative to WC-CoCr and Cr3C2-NiCr

TiC-based hardmetal coatings containing 25 or 40 vol% Ni-20 wt%Cr matrix (hereafter TiC-25NiCr and TiC-40NiCr) were obtained by High Velocity Oxygen-Fuel (HVOF) and High Velocity Air-Fuel (HVAF) spraying, starting from high-energy ball milled feedstock powders. These coatings are intended as critical raw materials-free solutions against wear and corrosion. HVOF-sprayed coatings contain some more oxide inclusions than do HVAF ones, but, irrespective of the deposition conditions, TiC-40NiCr coatings are usually somewhat harder (800-900 HV0.3) than TiC-25NiCr ones. They also exhibit lower wear rates in ball-on-disc sliding tests against Al(2)O(3 )at room temperature. A hard asperity can indeed penetrate slightly deeper into TiC-25NiCr, as it deforms inelastically through microcracking. Bigger abrasive grooves are thus produced. The wear resistance of TiC-40NiCr coatings compares favourably to that of a Cr3C2-25% (NiCr) reference, and even approaches that of WC-10 wt%Co-4wt.%Cr. TiC-40NiCr coatings are also more corrosion resistant than both reference materials when tested by electrochemical polarization in a 3.5% NaCl solution. At 400 degrees C, to the contrary, TiC-25NiCr coatings exhibit better sliding wear resistance, whilst more severe abrasive grooving and adhesive tearing affect TiC-40NiCr samples. TiC-NiCr coatings are also unaffected by the transverse macro-cracking that was found to compromise the usefulness of WC-CoCr at 400 degrees C.