State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering,Xi‘a(chǎn)n Jiaotong University, Xi’an 710049, China
Oxidation resistance of the abradable sealing coating is an important factor in determining its service life. However, the sealing coating possesses a porous structure with porosity up to 50%, which makes classical weight gain rate evaluation methods inapplicable. To evaluate the oxidation resistance of porous coating accurately, this work investigated the typical porous abradable sealing coating. First, oxidation kinetics of the coating and distribution of oxide film were systematically studied. Then, an inner surface oxidation mechanism of the porous coating was revealed. Finally, a reasonable method for evaluating the oxidation resistance of porous coating considering the actual oxidized surface area was established. Results showed that pores in the coating served as rapid diffusion channels for oxygen in the environment, significantly increasing in the contact area between the coating and the environment by several orders of magnitude, and an increase in the calculated oxide film thickness by several orders of magnitude than the actual oxide film thickness. Based on this, this work calculated the actual oxidation area by establishing a porous coating model and thus established an evaluation method of the oxidation resistance. According to the proposed evaluation method, the average oxidation rate at 600 ℃ under air condition of NiCrAlbentonite abradable sealing coating prepared in this work was 1.8×10-2 g·m-2·h-1, which had reached the level of complete oxidation resistance based on standard HB5258—2000. The established evaluation method is meaningful for accurately evaluating the oxidation resistance performance of porous coatings to ensure their reliable service.