Formation of Abradable Ceramic Coatings Through Deposition of Semi-Molten Ceramic Particles by Flame Spray

The high temperature gas turbine requires ceramic abradable coating for sealing to ensure high efficiency. In this study, a novel method is proposed to deposit the porous ceramic coating through deposition of ceramic spray powder particles at semi-melted state. The commercially available Al₂O₃ powders were spheriodized and screened to a particle size range from 40 to 50μm for spray deposition. Flame spraying was employed for coating deposition. During deposition, the substrate surface was kept at 500oC. The effect of melting degree of spray particles on coating microstructure was investigated by changing flame power and spray distance. The porosity of flame-sprayed Al₂O₃ coatings was estimated by image analyzing from coating cross-section. The results showed that the porous Al₂O₃ coatings were successfully prepared of the porosity of 40%-59% by flame spray. Moreover, spray parameters such as acetylene flow rate and spray distance have significant influences on particle melting state, thus the microstructure and the porosity of the coating. With the decrease of acetylene flow rate and spray distance, the porosity of coating increased due to the decrease of the melting degree of spray particles. At a spray distance of 20 mm, when the acetylene flow rate was reduced from 400 to 200 L/h, the porosity increased from 37% to 59%. The results clearly demonstrated the feasibility to prepare the porous abradable coating of high porosity through surface-melted spray particles.