Oxidation of HVOF Sprayed Alloy Coatings and Its Control by a Gas Shroud

Abstract

Abstract Oxidation of HVOF sprayed 316L stainless steel coatings was studied experimentally. Oxygen content in the sprayed coatings was analyzed and its dependence on several spray parameters such as spraying distance, mixture ratio of fuel to oxygen, and composition of atmospheric gas on the substrate was studied. The oxygen content in the original powder was about 0.03 wt%, which typically increased to 0.3 % in the HVOF sprayed coatings under the standard spraying conditions. Reduction of spray distance significantly increased the oxygen level due to the excessive heating of substrates by the flame. The sprayed deposits were analyzed by XRD and the oxides within the coatings were identified as magnetite Fe3O4 or chromite FeCr2O4. By using a nitrogen-gas shield attached to the substrate, it was revealed that the oxidation during flight is around 0.2 wt%. Control of oxidation by attaching a gas shroud to the HVOF nozzle has been attempted and oxygen content below 0.15 % has been achieved so far while maintaining deposition efficiency over 73 %.