Enhanced high-temperature oxidation resistance of Mg-Gd-Zn-Zr alloy by YSZ TBC with PEO bond layer

Magnesium alloys suffer from significant limitations in high-temperature applications due to poor oxidation resistance, primarily attributed to the non-protective nature of their native MgO scale (Pilling–Bedworth ratio, PBR = 0.81). This study investigates a novel thermal barrier coating (TBC) system, YSZ/PEO/Mg, designed to enhance the high-temperature performance of a Mg-Gd-Zn-Zr alloy. The system consists of an atmospheric plasma sprayed (APS) 8YSZ top coat deposited onto a plasma electrolytic oxidation (PEO) bond layer applied to the Mg substrate. For comparison, a YSZ coating deposited directly on the Mg substrate (YSZ/Mg) was also prepared. Both TBC systems exhibited stability during 100-hour cyclic oxidation at 200 °C. However, under cyclic oxidation at 400 °C for 100 min, the YSZ/Mg coating experienced catastrophic spallation due to interfacial oxidation and thermal stress, exposing the substrate. In contrast, the YSZ/PEO/Mg system maintained excellent integrity. Crucially, a continuous and protective gadolinium oxide (Gd₂O₃) thermally grown oxide (TGO) layer (PBR = 1.29) formed at the Mg/PEO interface during high-temperature exposure. Furthermore, the porous structure of the PEO layer facilitated mechanical interlocking of the YSZ top coat, significantly enhancing interfacial bonding strength. These results demonstrate that the YSZ/PEO/Mg TBC architecture, leveraging the synergistic effects of the PEO bond coat and the protective Gd₂O₃ TGO, provides an effective solution for significantly improving the high-temperature oxidation resistance of magnesium alloys. This approach is particularly promising for demanding applications such as aerospace thermal protection systems.