Flattening of an individual particle on the substrate is a unit cell for the coating formation in plasma spraying. In this study, individual Cu splats and coatings were collected on the AISI304 substrates at different temperatures by plasma spraying. Microstructures of the splats and coatings were observed by scanning electron microscope, and the adhesion strength of each coating was measured by tensile test. The coating hardness was also evaluated. The splats collected on the unheated substrate performed as splash shape, while most of the splats collected on the substrate at high temperatures exhibited as regular disc type. In particular, less nanopores could be found at the bottom surface of the disc shaped splats. The coating adhesion strength increased dramatically from 22 to 63 MPa with the increase in substrate temperature; the coating hardness also increased with the increase in substrate temperature. Accordingly, the coating performance has a close relation with the splats flattening behaviour on the substrates surface.
High-velocity oxygen/air fuel (HVO/AF) WC-17Co and WC-10Co4Cr coatings exhibit great potential in the replacement of electrolytic hard chrome (EHC) plating, and comprehensive properties of such coatings should be superior to those of electrolytic hard chrome plating. The impingement resistance of HVAF WC-based coatings sprayed on 300M ultrahigh-strength steel was studied in this paper. As an important property index, the fracture toughness of HVAF WC-based coatings was measured using the microindentation method at loads of 9. 8, 19.6, 24.5, 29.4, and 49.0 N, respectively. The cracks resulting from stress concentration in the microindentation were analyzed. The impingement resistance for two HVAF WC coatings and EHC was evaluated according to the ASTM D 3170 standard, and steel ball free-fall experiment was performed at the height of 0.61, 1.52, 1.83, 2.36, and 2.59 m, respectively. The cracks caused by both impingements were analyzed using scanning electron microscopy (SEM) and optical microscopy (OM) in comparison with the cracks in microindentation test.
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