This study provides an investigation into the influence of surface roughness, porosity, and chemistry on the wettability and infiltration behavior of calcia-magnesia-alumino-silicates (CMASs) in thermal and environmental barrier coatings (T/EBCs) used in high-temperature gas turbine engines. High-temperature contact angle measurements were performed at 1260 °C on 7 wt.% yttria-stabilized zirconia (7YSZ) and yttrium ytterbium disilicate (YYbDS, (Y_1/2Yb_1/2)₂Si₂O₇) to evaluate the interaction of CMASs with different surface finishes and coating microstructures. The findings demonstrate that porosity plays a dominant role in determining CMAS infiltration dynamics. In YYbDS, increasing porosity from 6.3% to 22.7% facilitated the formation of an apatite layer that limited CMAS penetration to approximately 2 µm. Surface roughness exhibited a subtler influence in that reducing Sa from 0.61 µm to 0.05 µm increased the change in the contact angle by ~2°, although its impact was found to be less significant compared to porosity and reactive chemistry. These results indicate that an integrated approach that optimizes porosity, chemistry, and surface morphology can significantly enhance CMAS resistance. The study emphasizes that leveraging both microstructural and chemical properties is critical to developing coatings capable of withstanding the harsh conditions encountered in aerospace environments.

High temperature exhaust ducts in modern gas turbine engines are exposed to particle-laden flows in which solid particle erosion can limit service life and degrade performance. This study evaluates the erosion response of Inconel 625 and three oxide/oxide ceramic matrix composites (Ox/Ox CMCs) reinforced with Nextel™ 312, 610, or 720 fibers under alumina jet impingement at 650 °C. Erosion experiments spanning impingement angles of 5° – 15° revealed angle- and material-dependent scar morphologies and degradation modes. Inconel exhibited ductile ploughing with discoloration from oxidation, whereas the CMCs showed brittle matrix removal and fiber fragmentation. Using exposure-normalized data, maximum wear depth versus impingement angle followed a power-law over 5° – 15°; however, invariance of depth wear rate across exposure was observed only for Inconel and N720. Elliptical contour fitting of profilometry maps enabled evaluation of a volume-to-surface area metric that plateaued at approximately 28 % of the maximum depth across materials, facilitating translation from concentrated jet erosion to an effective uniform erosion estimate. Scanning electron microscopy imaging revealed that Inconel’s erosion morphology varied strongly with impingement angle, while the CMCs displayed anisotropic fracture features governed by fiber orientation. These results provide a quantitative baseline for comparing composite and metallic materials and support the feasibility of Ox/Ox CMCs as potential erosion-resistant alternatives to conventional alloys in exhaust systems.