Coatings enrichment by carbide dissolution

Surface welding of hard alloys allows for the protection of components exposed to severe wear. Nevertheless, deposition of these hard alloys requires special procedures in order to minimize cracks and other welding defects. This work evaluated an alternative procedure to reduce welding defects as hard surfaces were produced. For that purpose fine WC-Co were mixed with iron powders and with an atomized cobalt based alloy, respectively, and processed with Plasma Transferred Arc (PTA). Powder mixtures with 5 wt.% and 35 wt.% WC-Co were deposited with two current intensities 150 A and 170 A on carbon steel plates. It was aimed to melt and dissolve the carbides to produce defect free hard iron based and cobalt based coatings. Surfaces were characterized for their soundness, hardness and microstructure regarding the effect of powder mixture chemical composition and current intensity used during processing. Visual inspection, dilution measurements, X-ray diffraction of powder mixtures and coatings, Vickers microhardness, optical and Scanning Electron Microscopy and pin-on-disc tests were used for surface evaluation. Results showed that PTA deposition allowed for the enrichment of coatings as carbides were melted in the plasma arc and dissolve in the different matrix.