Influence of Carbide Size and Co Content on Deposition Behaviour and Microstructure of WC-Co Coatings in Cold Spraying

Thermally sprayed WC–Co cermet coatings are used extensively for numerous wear-resistant applications in a variety of industrial environments. However, the decomposition of the WC and amorphization of the metallic phase during spraying process would degrade coating performance. Cold spraying (CS) process with ability to retain the feedstock microstructure into coating due to its low spraying temperature offers potential to deposit WC–Co coatings with enhanced performance.

However, it is difficult to deposited WC-Co cermet coatings by cold spraying process due to the limited deformation ability of feedstock powder. It is known that the cermet coating formation do not depend only on the spray processes and parameters, but also on the feedstock powder characteristics such as carbide size, metal binder content, particle morphology and so on. Therefore, in the present paper, the WC-Co coatings with different carbide size (0.2, 0.8 and 2.5 μm) and different Co content (12, 17 and 23 wt.%) were produced by cold spraying process. The effects of both carbide size and Co content on the particle deposition behaviour and microstructure of cold-sprayed WC–Co coatings were studied in order to understand the factors surrounding the formation of dense WC-Co cermet coatings in cold spraying process. The results showed that all deposited WC-Co coatings had no observable phase changes in cold spraying process. It was observed from the top surface and cross-section of individual WC–Co particles that the flattering leading to particle deposition significantly depended on Co content and increasing Co content would bring about the fuller flattening of WC-Co particles and higher deposition efficiency. In addition, decreasing carbide size of feedstock powder under the condition of keeping the same Co content would led to effective building-up of dense WC-Co coatings and higher coating Vickers hardness.