(V) High Temperature Erosion Mechanisms and Erosion Rate of Hard Overlays/Coatings for Surface Recovery of Heavy-Fuel Engines

This study aims at evaluating the erosion resistance and erosion rate at temperature of several overlays and coatings, including: laser cladding of Stainless Steel (SS-420); bilayers of SS-420/Inconel 718, and SS-420/Stellite 6; CrC-NiCr and WC-CoCr by HVOF; Fe-based alloy and Ni-Al 95/5 alloy by Arc Spray; NiCrBSiFe and NiCrBSiFe-WC by powder flame spraying. These overlays and 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 tests consist of erosive particles of Al₂O₃ thrown through a high temperature gas jet, for 5 cycles of 5 minutes, according to ASTM G211-14, modified for high temperature. Coated samples of 10 mm thickness are kept with a front temperature of 450ºC and a back temperature of 90ºC (water cooled), simulating the actual application. The eroded samples are characterized using SEM/EDS, and x-ray diffraction analysis. The results show erosion rates of each material/system, and their corresponding erosion mechanisms. The studied samples were also subjected to high temperature corrosion tests in a molten salt environment of V₂O₅ and Na₂SO₄ (results will be presented in another paper at IMAT-2020). Finally, the results allows for the selection of an optimum overlay/coating for this surface recovery application towards promoting a re-manufacturing strategy of cast iron components for heavy duty engines.