Thermal barrier coatings for gas turbines: Plasma spray or EBPVD?

Thermal Barrier Coatings (TBCs) are widely used to reduce the metal substrate temperature and, as a consequence, extend part life. Plasma sprayed TBCs are most commonly used, because of the versatility of the system in being able to deposit a wide range of compositions, lower capital and operating costs, and the ability to spray large parts. However, due to inconsistent deposit properties and the inherent morphology of the coatings, they are generally limited to static and non-critical locations. EBPVD, or Electron Beam Physical Vapour Deposition, produces coatings that are very smooth, very controllable porosity and structure and of consistent quality. However, due to the high capital costs and limited part size capabilities, EBPVD is generally limited to the more critical locations. Intensive developments in plasma (thermal) spray processes have led to significant improvements in production quality and resistance to thermal spallation. These, combined with a better understanding and use of alternate coating materials, have blurred the distinctions between the two processes. Some recent developments with both processes will be the subject of this paper.