Cermet coatings prepared by pulsed gas dynamic spraying process: Effect of the process parameters

The work presented is part of a research program aimed at exploring the possible advantages of the pulsed gas dynamic spraying (PGDS) process, as an alternative production technique of WC-based cermet coatings. In the PGDS process the feedstock particles are accelerated and heated in a high velocity flow before impacting the substrate to be coated. In this study the effect of the processing conditions, in particular the gas temperature, the spray pressure, the standoff distance, and the initial particle temperature on the cermet coating microstructure is investigated. Monitoring of the particle velocity at the gun exit is conducted using a laser diagnostic system in order to correlate it with the various spray parameters. Different analysis techniques (OM, SEM, XRD, and microhardness) are used to characterize the coatings produced. Detailed comparisons of powders and coating microstructure, phase composition, and microhardness are presented and discussed. The results show that an increase in spray temperature and in-flight particle velocity, obtained by increasing the gas temperature and pressure, leads to a decline in the volume fraction of defects within the coating as well as improvement of the substrate/coating interface. High deposition efficiency with low coating porosity level was obtained by decreasing the standoff distance and preheating the feedstock powder. Spraying onto Al-6061 and SS-304L type of substrates did not reveal a significant effect on the coating microstructure.