This study aims at evaluating the erosion resistance at temperature of several hard coatings, including: CrC-NiCr by HVOF, Fe-based alloy by Arc Spray, NiCrBSiFe by powder flame spraying. These coatings are to be used for the recovery of highly eroded walls (above 10 mm thickness) of gray cast iron in the exhaust ducts in heavy-fuel engines. The erosion test consists of erosive particles thrown through a high temperature gas jet, for 5 cycles of 5 minutes, according to ASTM G211-14 (modified). Coated samples are subjected to a fuel gas-torch reaching a front temperature of 450ºC and a back temperature of 90ºC (water cooled), simulating the actual application. The eroded samples are characterized using EDS, and SEM. The results show the erosion rate of each material/system, and their corresponding erosion mechanisms. Thus, the results allows for the selection of an optimum coating for this surface recovery application.

The mechanical integrity of WC-Co coatings is critical for their performance in wear, corrosion, and impact resistance applications. Residual stress, with its role in development of cracking, micro-cracking, and delamination, is another integral part of the mechanical characterization of the coated systems. In the given study, the residual stress of the WC-Co coatings on steel and stainless steel substrates was examined in two conditions, after deposition and after subsequent surface grinding. Several experimental techniques, including bi-layer curvature, X-ray diffraction, and neutron diffraction, were used to assess residual stress in the coatings and to enable comparison between the methods. Residual stresses induced by deposition are mostly due to rapid particle quenching and solidification upon impact, as well as any cold working induced by high velocity particle impact, but for the WC ceramic particles both effects are insignificant and result in small deposition stress. Thermal mismatch between materials of coating and substrate is the major source of stress and scale accordingly to the CTE of the substrate and coating materials and deposition temperature. It was demonstrated that the grinding applied to surface does not modify the as-sprayed residual stresses in the coatings significantly therefore assuming absence of microcracking that could have potentially affect the residual stresses.