Migration of Oxides in a Composite Coating and Its Effect on Inhibiting Coating Degradation

Based on the fact that the dispersed rare earth oxide particles in an electrolytic co-depositedNi-R_2O_3 layer migrated and accumulated at the substrate/coating interface immediately afteraluminizing,the mechanism of migration of the oxides and its effect on the behaviour of degradationof the coatings oxidized at 1100℃ were studied in this paper.The Ni-R_2O_3 layers were treated invacuum at 900℃ and aluminized at 1100℃ separately.The results indicated that the migration andaccumulation of R_2O_3 particles were favorable to the gathering of R_2O_3 at higher temperatures,andthe small size oxides were easier to migrate and gather.The drawing effect of grain boundary wasused to explain this behaviour.The microstructures of the coatings oxidized at 1100℃ were ob-served.It was found that the coating degradations were related to the amount and distribution of theaccumulated R_2O_3 at the alloy/coating interface.Three typical kinds of the accumulated layerswere identified.The continuous oxide layers acted as diffusion barrier which could inhibit the coat-ing degradation effectively.

Migration of Oxides in a Composite Coating and Its Effect on Inhibiting Coating Degradation

Based on the fact that the dispersed rare earth oxide particles in an electrolytic co-deposited Ni-R_2O_3 layer migrated and accumulated at the substrate/coating interface immediately after aluminizing,the mechanism of migration of the oxides and its effect on the behaviour of degradation of the coatings oxidized at 1100℃ were studied in this paper.The Ni-R_2O_3 layers were treated in vacuum at 900℃ and aluminized at 1100℃ separately.The results indicated that the migration and accumulation of R_2O_3 particles were favorable to the gathering of R_2O_3 at higher temperatures,and the small size oxides were easier to migrate and gather.The drawing effect of grain boundary was used to explain this behaviour.The microstructures of the coatings oxidized at 1100℃ were ob- served.It was found that the coating degradations were related to the amount and distribution of the accumulated R_2O_3 at the alloy/coating interface.Three typical kinds of the accumulated layers were identified.The continuous oxide layers acted as diffusion barrier which could inhibit the coat- ing degradation effectively.