Mitigating CMAS attack during thermal cycling via triple-scale micro/nano structured thermal barrier coatings

Silicate deposits, predominantly composed of CaO-MgO-Al₂O₃-SiO₂ (CMAS), are known to cause severe degradation of thermal barrier coatings (TBCs) employed on turbine blades. In this study, the TBCs consisting of ytterbia doped gadolinium zirconate (GYbZ) top layer and yttria stabilized zirconia (YSZ) bottom layer, with conventional dual-scale micro/nano structure, was prepared by plasma spray-physical vapor deposition (PS-PVD). To further enhance CMAS resistance, surface modification of the as-deposited coatings was achieved by ultrafast laser direct writing technology (ULDWT), leading to a novel triple-scale micro/nano structure. The thermal cycling performance of both TBCs was evaluated under flame thermal cycling conditions with concurrent CMAS exposure. The ultrafast laser ablation yielded evenly spaced micro-conical pillars with characteristic aspect ratio and uniformly distributed nanoparticles, which significantly reduced CMAS melt adhesion and wetting. Furthermore, grain boundary density was significantly increased, which facilitated the rapid formation of a dense reaction layer at the CMAS/GYbZ interface, thereby effectively impeding CMAS infiltration. As a consequence, the thermal cycling lifetime for the novel triple-scale structured TBCs under simultaneous flame thermal shock and CMAS attack (>4000 cycles at 1300 °C) was markedly improved, representing an improvement of over 50 % compared to conventional TBCs. Our approach indicates that surface nanostructuring can be a powerful tool to enhance the performance of TBCs under extreme conditions.