Oxidation Restriction of In-flight Particles upon GS-HVOF Spraying by Nitrogen Addition to Combustion Gas

Abstract

In order to improve the environmental barrier property of coatings fabricated by the HVOF spray process with a gas shroud, their oxygen content of 0.19 mass% as the lowest conventional figure was still more reduced by changing the composition of combustion gas. Introduction of nitrogen gas to the combustion chamber lowered the temperature of the in-flight spray particles while maintaining their high velocity. This method could reduce the oxygen level of a HastelloyC coating to 0.063 mass% at the lowest present value, which is comparable to that of the feedstock with 0.042 mass%. Other coating with 0.14 mass% could be obtained along with the open porosity below 0.1 vol%. The latter coating exhibited the improved environmental barrier property in artificial seawater.