Influence of Substrate Cooling Method on Compositional Shift and Deposition Efficiency of HVOF-sprayed WC-Co Type Coatings

Modern, high-throughput HVOF and plasma coating operations require an effective and precise control of substrate temperatures during deposition in order to achieve optimum performance of the final part and minimize operation time.  Although frequently overlooked, substrate cooling method may influence interfacial stress-controlled coating adhesion, as well as deposition efficiency of powder, and oxidation resultant compositional shift in the deposited material. 

This paper presents results of experimentation comparing cooling rates of selected media including compressed, room temperature air and nitrogen, cryogenically liquefied carbon dioxide (LCO2), and nitrogen (LIN).  Oxidizing effect of these cooling media on two types of WC-CoCr feed powders is also reported.   HVOF spraying tests show, that substrate cooling media may affect coating oxidation in a similar manner as feed powders.  Chemical analyses of deposited coatings point to a close relationship between the extent of oxidation under cooling media and powder deposition efficiency.  Cooler and more inert gases are found to maximize deposition efficiency. Presented results include SEM and XRD analysis.