Effect of N2 and He Carrier Gases on Oxidation Behavior of Cold Sprayed CoNiCrAlY Powder to Deposit Bond Coats

Abstract

CoNiCrAlY has been cold sprayed onto 316L substrate using helium and nitrogen as carrier gases. CGDS with helium gas under the temperature of 400 °C and pressure of 20 bars and CGDS with nitrogen gas under the temperature of 450 °C and pressure of 38 bars were used. The purpose of the current study was to investigate the microstructure and oxidation behavior of CoNiCrAlY coatings deposited by CGDS technique with both carrier gases. The quality of the as-sprayed and oxidized bond coats was assessed and investigated from the point of view of microstructural (porosity and oxide concentration) and mechanical properties (hardness) characteristics. Sprayed samples were exposed to isothermal oxidation at 900 °C in air. Oxide growth rates were obtained from a series of mass gain measurement while oxide scale compositions were determined using SEM, XRD and EDX analysis. Helium processing condition displays more compact structure for the coating when compared to N2. The oxide scale on the CGDS sprayed with He coating after 1,000 h of oxidation is composed of alumina without the presence of detrimental fast growing mixed oxides. Results obtained in this study show that CGDS sprayed with N2 coating features high levels of visible defects, oxide content, spinal-type oxide and high oxide growth rate, whereas CGDS with He shows low oxide growth rate due to low porosity and oxide content.