Formation mechanisms of columnar/dense structure for Gd2Zr2O7 ceramics coatings with superior CMAS corrosion resistance

Abstract

Corrosion failure induced by calcium-magnesium-alumina-silicate (CMAS) deposits represents a predominant degradation mechanism in advanced thermal barrier coatings (TBCs) systems. In this study, a laser-based surface modification strategy was systematically investigated to reconfigure the microstructure of air plasma spray (APS) Gd₂Zr₂O₇ (GZO) coatings, with the aim of enhancing their resistance to CMAS corrosion. Numerical simulations revealed that laser power dictates microstructural transformations: a fully dense layer forms near the surface at 8 W; in contrast, at 12 W, honeycomb-like crystals are first nucleate at the bottom of the melt pool and grow upward, exhibiting a slight orientation bias in the laser scanning direction. Subsequently, a micro-columnar structure develops in the middle and upper regions of the melt pool. A parameter combination (laser power: 14 W, scan speed: 100 mm/s, line spacing: 0.02 mm, spot diameter: 0.5 mm) was selected to fabricate a hybrid surface texture, which consists of vertically aligned micro-columns (∼10 μm) atop a dense subsurface layer (∼15 μm). The resulting micro columnar and micro-nanocomposite structure conferred superior CMAS corrosion resistance, which is attributable to reduced CMAS wettability on the coating surface and limited CMAS infiltration into the coating interior. The synergistic effects of surface texturing and subsurface structural engineering provide new insights into the design of the corrosion-resistant TBCs via laser-induced phase-selective recrystallization.