Oxidaton Of Metallic Particles In Atmospheric Plasma Spraying And Its Effect On Thermal Barrier Coating

Thermal barrier coatings(TBCs), made of a ceramics top coat and a metallic bondcoat, are one of the most widely used coatings. The utilization of TBCs, providingmajor reduction in the surface temperature of the workpiece, can prolong the servicelife of the hot sections and improve the work efficiency of engines. Atmosphericplasma spraying (APS) is one of the main manufacturing methods of TBCS, however,the atmospheric plasma sprayed coating contains a high impurity content and lowdensity and low bond strength, which has serious effect on the performance of coating.Through investigating the oxidation behavior of metallic particles during atmosphericplasma spray process and their effect on coating microstructure with iron particles andNiCoCrAlY particles, a argon shrouding was developed which can decrease theoxidation of particles during atmospheric plasma spray process. The comparisonbetween the two types of sample that with and without using argon shrouding wasconducted. The effect of the oxidation of particles on the coating performance ofcoating was discussed.The results showed that the oxidation of inflightparticles was controlled by itsspray distance. The oxidation level increased with the spray distance increased. Theoxidation of particles was mainly convective oxidation as the spraying distance wasless than certain distance(45mm). After the distance was more than critical value, theoxidation would be governed by diffusion. In the atmospheric plasma spray process,both the inflightoxidation and the postimpactoxidation took place. For iron particles,the oxidation degree which increased after particle impacts with substrate was nearlythe same as that formed in the flight. For NiCoCrAlY particles, the oxidation wasmainly occurred during flight. The inflightoxidation of particles can significantlyinfluence the microstructure of coatings. The oxides trapped between splats wasoriginated from the oxide shells formed on the surface of inflightparticle, the oxidetrapped inside splats was originated from the oxide formed on the core of particles.Adding argon shrouding can reduce the entrainment of ambient air into the plasmajet and improve the melting of original powder, which also decrease the oxygencontent by 41.56% and the porosity by 34.38% by compared with atmospheric plasmasprayed bond coats. Adding argon shrouding can also improve oxidation resistance ofTBCs and decrease oxidation rate of TBCs by 20.37% by compared with atmosphericplasma sprayed TBCs during high temperature oxidation process...