Dynamic CMAS Deposition on APS-Produced 8YSZ Coatings: Effects of CMAS Powder Spray Angle and Coating Surface Conditions

Abstract

The ingestion of siliceous particulate debris into gas turbine engines during operation leads to the deposition of calcium–magnesium–alumino-silicate (CMAS) on the hotter surfaces of thermal barrier coatings (TBCs). At temperatures exceeding 1200 °C, these particles penetrate the TBC, resulting in the loss of strain tolerance and premature failure of the TBCs. Previous studies have largely focused on static CMAS testing, which does not fully replicate real engine conditions. To better simulate real-world scenarios, a commercially available CMAS (AFRL-03) powder was deposited by an atmospheric plasma spraying (APS) process onto 8YSZ coatings. The effects of different spray angles (90°, 60°, and 30°) of the CMAS powder on various TBC surfaces, i.e., as-sprayed, laser-glazed, and polished, were systematically evaluated. SEM/EDS analyses were used to characterize the morphology and elemental composition of the resulting CMAS deposits. Results showed that the polished and laser-glazed surfaces exhibited comparable CMAS weight gain, whereas the as-sprayed coatings accumulated the lowest amount. With respect to spray angles, a 30° impact angle produced the least CMAS deposition compared with 90° and 60°. Furthermore, neither surface temperature (525-1100 °C) nor coating porosity (10-25%) significantly affected CMAS infiltration, likely due to the short impingement duration and relatively low surface temperatures. However, at high temperatures ~ 1500 °C, CMAS infiltration into the pores and cracks of the 8YSZ coatings became evident. In addition, smoother surfaces promoted the formation of more uniform, spherical splats, while rougher surfaces tended to produce shattered or fragmented deposits.