Ceramic Thermal Barrier Coatings (TBCs) on superalloy components are being used successfully in land-based gas turbine and aircraft engines. These coatings are generally made by either air plasma spraying (APS) or electron beam physical vapour deposition (EB-PVD). In general, EB-PVD TBCs have superior durability due to the columnar structure, but they are very expensive compared to APS TBCs. EB-PVD TBCs are used primarily in the most severe applications such as turbine blades and vanes in aircraft engines. This paper presents an economical process to make durable TBCs, called Axial Suspension Plasma Spray (ASPS). This technology combines Mettech’s axial injection plasma process and automatic suspension feed system. The resulting TBCs exhibit columnar structures with vertical cracks, similar to EB-PVD coatings. Such structures allow the TBC to compensate for thermal expansion differences between it and the base material. The ASPS process presents an economical alternative to EB-PVD to produce durable columnar TBCs.

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.