Cold gas dynamic spraying of WC-Ni cemented carbide coatings

The feasibility of using a low pressure cold spray system for the deposition of WC-Ni coatings was studied. The Ni content was varied from 4 to 50 wt.% and the resultant coating properties were compared to WC-12Co-xNi powders, deposited using the same Ni contents. A Taguchi mixed level design of experiments method was used to optimize the spray parameters of each of the eight powder combinations. The optimal coatings predicted using this method were the WC-25Ni and WC-12Co-50Ni combinations. However the maximum experimental coating hardness was obtained for the 4 wt.% Ni coatings. A limitation of the Taguchi method is that it does not account for the effect of strain hardening that occurs as a result of the impact of the hard carbide particles. Low porosity coating build-up with non-homogenous distribution of the carbide phase was observed for all coatings. XRD analysis of the coatings indicated that no phase transformations or grain refinement took place during deposition. The morphology of the starting powders influenced coating properties. The dense WC particles had limited deformability and resulted in the fracture of the hard WC particles during deposition. The porous structure of the spherical and agglomerated WC-12Co powders was more deformable allowing for particle densification and elongation during deposition which resulted in higher WC retention within the Ni matrix. (C) 2014 Elsevier Ltd. All rights reserved.