Effects of Post-spray Heat Treatment on Hardness and Wear Properties of Ti-WC High-Pressure Cold Spray Coatings

In this research, the effects of post-spray heat treatment at 550 and 650 °C for 1 h on a cermet Ti-WC nanostructured coating deposited onto AISI 304 stainless steel substrates by high-pressure cold spray was observed. A metallic Ti interlayer was further used to compensate for stresses resulting from subsequent heat treatment on the developed coating. Microstructural analysis of the as-deposited coating by scanning electron microscopy (SEM) showed mostly fine WC grain (below 1 µm) present in the coating with a few larger 4 µm grains dispersed homogeneously throughout. X-ray diffraction analysis of the as-sprayed coating showed no noticeable evidence of WC decarburization. Heat treatment of the coating caused porosity to decrease from above 1.7% to below 0.5%, traced by SEM image analysis. Post-spray heat treatment promotes the formation of new carbide phases caused by the reactions between the Ti binder and WC grains, resulting in significant increases to Vickers microhardness. Evidence of an SHS reaction that produces TiC with heat treatment is confirmed with SEM image analysis as well as (S)TEM area mapping techniques, further supported by selected area electron diffraction analysis. Three-body sliding wear/abrasion tests have shown that wear resistance of Ti-WC cold spray coatings increases with heat treatment as well. In all, the effect of post-spray heat treatment behavior of nanostructured Ti-WC coating will be compared with that of as-sprayed behavior and WC-Co cold spray coatings.