Slurry sprayed thermal barrier coatings for aerospace applications.

Thermal Barrier Coatings (TBCs) were introduced to reduce operating temperatures and thermal stresses in structures and machine components across a wide range of industries and applications more than 40 years ago, and within the last 15 years their use in various high temperature applications has increased dramatically. These include the aeronautical, aerospace, automotive and nuclear industries and heavyduty utilities such as diesel trucks. The research and development of TBCs were centred on ceramic coatings possessing a relatively low thermal conductivity which is critically important for the thermal protection of load bearing structures. There are many manufacturing techniques for depositing ceramics coatings on a metallic substrate. Many of these techniques are very expensive and often inapplicable to coat large or curved surfaces. In this work a new, relatively simple and low cost method of manufacturing TBCs, the Slurry Spray Technique (SST), was developed by the candidate with a focus on aerospace applications. The challenge in the development of this technique was to achieve the coating quality comparable to the quality of the coating manufactured with the existing manufacturing techniques. The research began with the Wet Powder Spray (WPS), a promising and cost effective technique for fabricating TBCs, which was adopted by the candidate. However TBCs fabricated with this technique normally have an extremely low quality in comparison to the existing fabricating techniques, such as Electron Beam Physical Vapour Deposition or Atmospheric Plasma Spray. Through the analysis and examination of the individual fabricating stages of the WPS method, a new technique, Slurry Spray Technique (SST), was developed by the candidate and investigated. In particular, it was demonstrated that the TBC fabricated with SST have higher quality, strength and reliability than coatings fabricated with the WPS technique. The quality of TBCs achieved in this work is approaching to the quality of the thermal coating fabricated with commercially available manufacturing methods. The main advantages of the new technique are the low costs and ability to cover large and curved areas, which are critical for a number of important practical applications. This technique also allows the fabrication of multi-layered graded coatings, which were demonstrated to have a significantly improved performance in scale tests under conditions similar to a hypersonic flight than single layered coatings. The scale and virtual testings conducted with the help of the finite element modelling provided the confidence that with the future development of this technique it can be effectively utilised in numerous practical applications, specifically in the aerospace industry.Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 201