Mechanisms of Enhanced Thermal Durability in Porosity-Controlled Multilayer Thermal Barrier Coatings

This study investigates the enhancement of thermal durability in multilayer yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBC) with porosity-controlled structures. Conventional single-layer YSZ and multilayer TBCs with dense and porous layers were fabricated by air plasma spraying and the TBC specimens were subjected to furnace cyclic testing. The single-layer TBC suffered from catastrophic delamination under cyclic thermal loading, driven by the mismatch in thermal expansion, while the multilayer TBCs exhibited a significant increase in thermal durability, by up to 50%. The relevant delamination mechanism was suggested with microstructural analysis, showing that the multilayer structure effectively relieved residual stresses by forming horizontal cracks, thereby mitigating crack propagation. This study emphasizes that the multilayer design in TBC with controlled porosity significantly enhances thermal durability, improving the operational lifespan of gas turbine hot components.