Process Maps for Multimodal and Conventional WC-12Co Coatings

One type of multimodal (comprised of a mixture of nanosized and micronsized WC particles) and two types of conventional WC-Co powders were thermally sprayed by HVOF. Three types of HVOF torches, JP5000, DJ2600- hybrid (H₂) and DJ2700-hybrid (C₃H₆), were employed to produce a total of 66 different WC-Co coatings. For all the coatings produced, the in-flight particle temperature and velocity during deposition, deposition efficiency, hardness and abrasion resistance were measured. These measured properties and characteristics were used to construct process maps (via inverse distance weighting) in order to (i) establish relationships between the various process parameters, properties and performance characteristics and (ii) identify process windows where “optimized” coatings could be produced. It was observed that the multimodal coatings exhibited a much larger processing window for the highest performance, i.e., these coatings demonstrated high abrasion resistance over a broad range of particle temperature and velocity, a characteristic not observed for the conventional coatings. The maps revealed other interesting differences between the multimodal and conventional coatings and among the coatings produced using the various torches. The study demonstrates the value of process maps in producing information for engineering optimized thermal spray coatings.