Suspension plasma spraying is gaining greater interest for emerging applications such as new thermal barrier coatings, next generation environmental barrier coatings and ceramic membranes as in solid oxide fuel cells. Mettech developed an axial injection plasma process coupled with an automatic suspension feed system, and demonstrated its capability to overcome the complexities of the process and deliver quality coatings. This paper aims at determining the durability and stability of the gun, suspension feeder and their components. A 120-hour duration test was performed, and the plasma torch and suspension feed parameters and performances were recorded. The test results indicate that the equipment and process are stable and reliable, and ready for industrial applications.

Plasma spraying was successfully applied for Thermal Barrier Coatings (TBCs), which typically possess a lamellar structure with a porosity of 5-20%. Control of the plasma process presents a big challenge when the goal is to achieve fully dense coatings, as required for some emerging applications such as solid oxide fuel cells (SOFCs) and dense TBCs. Fine powders produce finer lamellae, and result in denser coatings. However, powders finer than 10 microns are very difficult to feed consistently into a plasma torch. Liquid slurries offer a means to deliver fine particles to thermal spray torches. In this paper, an automatic slurry feed system was developed to consistently deliver micro and nano powder slurries. The slurries were injected axially into a high energy/high velocity plasma torch to generate dense coatings. The effects of plasma parameters and different feedstocks on coating microstructures are investigated; dense coatings for various applications are demonstrated.