Abstract
At high temperature, ceramic materials are known to undergo oxidative reduction in the presence of water vapour. Understanding the exact mechanism of the high-temperature reaction process requires experimentation at engine conditions, especially with relevant partial pressure of water vapour and flow velocities. For this purpose, a high-pressure flow reactor has been developed to study the interaction of a high-temperature steam jet with various advanced ceramic materials and environmental barrier coating samples in the laboratory.
This experimental setup bridges a crucial gap in understanding surface reaction rates and material erosion under elevated pressures, insights that were previously unattainable in conventional atmospheric tests. The findings are critical for designing next-generation protective coatings for gas turbine components such as seals, vanes, and combustor liners, ensuring extended durability in extreme operating environments.
The test conditions, which mimic the local water molecule number density of the turbine engine, include pure steam up to 1400 °C, pressures up to 5 atm, and velocities exceeding 200 m/s. Positioned just 1 mm from the test surface, the steam jet impinges at variable angles (30°, 45°, and 90°) for durations up to 50 hours. The interaction of silicon carbide (SiC) and hot-pressed ytterbium disilicate (Yb₂Si₂O₇) with high-temperature steam is analysed using advanced characterisation techniques, including interferometry, SEM, EDS, XRD, and XPS. These analyses reveal microstructural evolution, reaction depth, and morphological transformations, providing insight into the underlying reaction mechanisms.
To complement experimental findings, laminar reacting flow simulations using ANSYS computational fluid dynamics (CFD) tools are employed to provide insights into local species concentrations, velocity gradients, and shear stresses, thereby validating and refining the experimental setup. By elucidating the degradation mechanisms of high-performance ceramics in steam-rich environments, this research supports the development of more resilient thermal protection systems for next-generation gas turbines, contributing to improved efficiency and durability.
