Droplet size effects on the interfacial behavior between CMAS and GYbZ thermal barrier coating material surface

The erosion of molten calcium-magnesium-alumino-silicate (CMAS) deposits poses a severe threat to the durability of thermal barrier coatings (TBCs) in advanced turbine engines. While laboratory studies typically use millimeter-sized pellets, real ingested volcanic ash consists of fine particles, creating a disparity in assessing interfacial behavior. This study combines experimental investigations with molecular dynamics (MD) simulations to unravel the size-dependent interfacial dynamics between CMAS droplets and (Gd_0.9Yb_0.1)₂Zr₂O₇ (GYbZ) TBC material. We systematically varied the initial size of natural volcanic ash compacts (1–3 mm) and analogous CMAS droplets in simulations (2–6 nm). Our results demonstrate a significant size dependence in wettability and spreading, with smaller droplets exhibiting enhanced wettability due to their higher surface-area-to-volume ratio, which places a greater fraction of atoms under the influence of the substrate's interfacial force field. Although the interfacial reactions consistently form apatite and fluorite phases, with atomic mobility following Si > Ca > Mg > Al, the corrosion depth of molten CMAS is governed by chemical composition and remains independent of droplet size. These insights emphasize that employing representative finer CMAS droplet in testing is critical for the accurate design of corrosion-resistant TBCs.