WC-Based Coating Production by the Pulsed-Gas Dynamic Spraying Process: Coatings and Process Analysis

WC–based cermet coatings are well established as wear resistant materials for a variety of applications. Traditionally, these coatings are obtained using thermal spraying (TS) methods such as HVOF and plasma spraying.  However, due to the high temperature of the TS process, the WC–based feedstock powder tends to undergo a combination of decarburization, grain growth, oxidation, and dissolution/reaction between the WC and Co during spraying.  This behaviour results in the formation of hard and brittle phases.  Consequently, it is envisioned that the Pulsed-Gas Dynamic Spraying (P-GDS) process, which operates at temperatures preventing these transformations, may provide an interesting alternative. In the P-GDS process, the feedstock particles are accelerated and heated in a pulsated high velocity flow created by the passage of shock waves, prior to impacting on the substrate and deforming to produce the sought coating.In this paper, WC-based coatings have been produced using six different types of cermets powders that differed not only in microstructural features such as size and morphology but also in the chemistry and phases. The effect of the processing conditions (gas temperature, spray pressure, standoff distance, and initial particle temperature) on the cermet coatings and process efficiency is investigated using different analysis techniques (OM, SEM, XRD, and microhardness measurements). A detailed comparison of powders and coatings microstructures, phase compositions, and hardness are presented and discussed in detail. Correlation between the spray parameters and particle velocity is conducted using a laser diagnostic system.
It was found that the PGDS process preserves the microstructure of the feedstock powders (no significant degradation of the phase composition) and can produced dense and thick WC-based coatings. Thus, the process has revealed to be a promising technique for the deposition of WC-based coatings.