Understanding and Modeling CMAS and Thermal Barrier Coating Interaction Under Thermal Gradients

Abstract

When operating at very high temperatures (starting from 1200 °C), thermal barrier coatings (TBCs) start interacting with oxide particles such as CMAS (CaO-MgO-Al₂O₃-SiO₂), found in sand or volcanic ashes. Namely, CMAS can infiltrate the TBC and tamper the thermal and mechanical properties of said TBC, leading to its deterioration. This study aimed to understand the interaction between yttria partially stabilized zirconia (YSZ) TBCs and CMAS particles under a thermal gradient. The TBC was made through an EB-PVD process. The experimental study was conducted with a laser rig. TBC samples were heated up to 1200 °C and exposed to a cylinder-shaped CAS (CaO-Al₂O₃-SiO₂) deposit for different durations. The study was conducted in presence of a through-thickness thermal gradient of up to 150 °C in the sample. It was observed that the infiltration is a rather quick phenomenon; while, the dissolution of the TBC and the precipitation of the crystalline phases worked on a longer timeline. Both phenomena can then be considered uncoupled under these test conditions and modeled as such. A heat transfer model was implemented as to better understand the different phenomena happening. The model was fitted to experimental data through a test-calculation dialog.