Hard WC-Ti coatings deposited by cold gas spraying

Cold-gas spray (CGS) deposition of WC-Ti coatings starting from a commercial feedstock powder was investigated. The powder was constituted by a dispersion of WC micrometric particles (50% in volume) in a Ti matrix. The WC-Ti belongs to a new family of cermet coatings Ti-based, in which it is possible to obtain a high hardness due to a SHS (Self-propagating High temperature Sinthesys) reaction between the metallic matrix and the ceramic dispersion, e.g., during a post deposition heat treatment. It causes the nucleation of TiC, increasing the harness of the matrix. The possibility of activating the SHS reaction directly during the CGS deposition process (in flight), avoiding the need to carry out subsequent heat treatments, was investigated. Several process gas temperatures were used to investigate their influence on coating hardness and deposition efficiency. Microstructural characterization was carried out by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The coatings characterization confirmed that as the process gas temperature increases there is an increase in hardness, although at the expense of a loss of deposition efficiency. High hardness values (about HV100 1000) were measured. Tribological behavior was also evaluated by block-on-ring wear test.