C. J. Li, Y. Z. Xing, C. X. Li, G. J. Yang, School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an, China
The interaction of molten droplet with the deposited coating surface determines the cohesion of a plasma-sprayed coating. The increase of temperature of a ceramic molten droplet may contribute an improvement of wetting of droplet to coating surface. Consequently, the bonding at the interfaces between splats in the coating may be enhanced. However, it is generally much limited to raise temperature of spray droplet with conventional thermal spray heat sources. On the other hand, a preheating of substrate prior to deposition can increase the interface temperature between flattening droplet and substrate and subsequently enhance the bonding between lamellae. In this study, YSZ molten droplet created by plasma spraying was deposited on the YSZ substrate preheated to different temperature from 150oC to 1200oC to aim at understanding the formation mechanism and controlling of lamellar bonding. Both separated splats and multilayer splats were deposited. The influence of substrate surface temperature on splat morphology, grain size and characteristic of grains growth at the interfaces of both substrate/splat and splat/splat examined through SEM and TEM. It was confirmed that the morphology of splat is changed from irregular shape to a regular disk shape when substrate surface temperature is increased to 200oC. The microcrack network is formed on all splats deposited at the temperature less than about 800oC. The individual splats present columnar grain perpendicular to the interface between substrate and splat. When substrate temperature is increased over 800oC, a significant epitaxial growth of columnar grains through multisplats was observed. The results indicate that the bonding ratio between plasma-sprayed ceramic lamellae can be enhanced through substrate surface temperature.
Summary: The interaction of molten droplet with the deposited coating surface determines the cohesion of a plasma-sprayed coating. The increase of temperature of a ceramic molten droplet may contribute an improvement of wetting of droplet to coating surface. Consequently, the bonding at the interfaces between splats in the coating may be enhanced. However, it is generally much limited to raise temperature of spray droplet with conventional thermal spray heat sources. On the other hand, a preheating of substrate prior to deposition can increase the interface temperature between flattening droplet and substrate and subsequently enhance the bonding between lamellae. In this study, YSZ molten droplet created by plasma spraying was deposited on the YSZ substrate preheated to different temperature from 150oC to 1200oC to aim at understanding the formation mechanism and controlling of lamellar bonding. Both separated splats and multilayer splats were deposited. The influence of substrate surface temperature on splat morphology, grain size and characteristic of grains growth at the interfaces of both substrate/splat and splat/splat examined through SEM and TEM. It was confirmed that the morphology of splat is changed from irregular shape to a regular disk shape when substrate surface temperature is increased to 200oC. The microcrack network is formed on all splats deposited at the temperature less than about 800oC. The individual splats present columnar grain perpendicular to the interface between substrate and splat. When substrate temperature is increased over 800oC, a significant epitaxial growth of columnar grains through multisplats was observed. The results indicate that the bonding ratio between plasma-sprayed ceramic lamellae can be enhanced through substrate surface temperature.
