Abstract
Oxidation of HVOF sprayed 316 L 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 wt% in the HVOF sprayed coatings under standard spraying conditions. Reduction of spray distance significantly increased the oxygen level due to the excessive heating of substrates by the flame. 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 wt% has been achieved so far under a fuel-rich combustion condition while maintaining deposition efficiency over 73%. Coating porosity, however, increased from 0.5 to 2.5 vol% by using the gas shroud.
