Feedstock Powder Considerations for Miniaturized Inner-Diameter HOVF Systems for the Deposition of WC-Co-Cr Coatings

Emerging miniature HVOF systems offer new opportunities to replace hard-chrome plating with sprayed carbide coatings in space restricted inner-diameters in aerospace and industrial application.  The worldwide interest in this technology is largely driven by regularity restrictions for the continuation of downstream use of hexavalent chrome, such as REACH. While feedstock supply chains for conventional HVOF WC-Co-Cr are well established since decades, the lower flame enthalpies and shorter spray distances used for the scaled-down HVOF systems impose smaller particle size cuts as customized to the particular spray system to attain sufficient particle heating and acceleration. This presentation discusses the feedstock particle size and size distribution considerations for the liquid fueled Praxair TAFA Model 825 JPid, the hydrogen fueled Spraywerx ID-NOVA MK-6 HVOF, and the Uniquecoat i7 HVAF systems for the deposition of wear protective WC-Co-Cr coatings. A variety of custom manufactured and commercially available powders are compared and suitable windows for particle size distributions, torch input powers and spray distances are delineated for the deposition of coatings exceeding harness values of 950 HV_300gf, porosities below 1%,  and ASTM 65 abrasion wear loss below 0.1g per 6000 revolutions.