Corrosion and wear performances of alternative TiC-based thermal spray coatings

Abstract

Thermal spray WC-Co based coatings are considered among the best solutions against wear and corrosion of industrial components, but it is necessary to reduce their usage due to sustainability and safety issues. In this respect, the paper is focused on the deposition and characterization of TiC-bases coating systems with cobalt-free matrices. Three alternative formulations, TiC-33 vol%NiCr, TiC-40 vol%FeNiCr, TiC-18 vol%WC-33 vol%NiCr, manufactured by high-energy ball milling (HEBM) and deposited by HVOF, are employed in order to assess the effects of binder concentration, composition, and addition of some WC as second hard phase on their wear and corrosion resistance in comparison with WC-CoCr and Cr₃C₂-NiCr references. It was found that all coatings exhibit a combination of shallow abrasive grooving, surface fatigue (lamellar delamination) and tribo-oxidation under sliding conditions at room temperature. At 400 °C, surface fatigue is less relevant but abrasive grooving becomes more prevent and some adhesive wear also occurs. The performance of all coatings is intermediate between those of the WC-CoCr and Cr₃C₂-NiCr references. More specifically, the TiC-33 vol%NiCr composition exhibits similar performance as a TiC-25 vol% composition previously studied by the authors. The addition of WC led to the formation of a W-rich shell around the TiC particles through in-flight reactions during spraying. This limited in-flight oxidation of TiC but it could not prevent post-deposition oxidation of hot lamellae. Because interlamellar oxides formed at this stage have the most significant negative effect on wear resistance, overall the TiC-WC-NiCr composition did not exhibit any tribological advantage over pure TiC-NiCr. The Ti-FeNiCr composition is especially sensitive to surface fatigue but, to the contrary, provides good corrosion protection with no performance deficit compared to the same volume fraction of a NiCr matrix. All the TiC-based coatings are not suitable to protect against high-stress abrasion due to the overly negative influence of their interlamellar brittleness under these conditions.