Optimization of curing conditions for Si3N4–Al2O3/Y2O3 thermal barrier coatings on Glass Fiber-Reinforced Polymer: Balancing thermal insulation and mechanical strength

This study investigated the effects of heat treatment temperature and holding time on the thermal and mechanical properties of Si 3 N 4 -Al 2 O 3 /Y 2 O 3 ceramic–binder composite thermal barrier coatings (TBCs) applied to glass fibre-reinforced polymer (GFRP) substrates via slurry coating. The heat treatment process, conducted at temperatures ranging from 100 to 150°C and holding times between 5 and 7 h, primarily affected binder dehydration, polymerization, and coating consolidation rather than ceramic sintering or grain growth. Characterization revealed the formation of stable crystalline phases, including cubic Y 2 O 3 , orthorhombic SiO 2 , and cubic Al 2 O 3 , originating from the starting ceramic powders and retained after heat treatment, which contributed to the coating stability. These phases act collectively within the ceramic–binder system, and their individual roles were not distinguished in this study. Optimal heat treatment conditions at 125°C for 5 h yielded a TBC with a bond strength of 1.740 MPa, porosity of 10.350%, and effective thermal insulation, reducing the GFRP surface temperature to below 151.667°C under a 700°C thermal load, while exhibiting a mass loss of 11.742%. Increased heat treatment temperature and holding time enhanced the adhesion strength but reduced the thermal insulation owing to densification and lower porosity. Two-way ANOVA showed significant effects of curing temperature and holding time on coating performance, with valid assumptions and no interaction between the factors. This study highlights the critical role of low-temperature heat treatment parameters in controlling binder chemistry and microstructural evolution in ceramic–binder composites. These factors are essential for balancing the mechanical strength and thermal performance of ceramic-based TBCs applied to lightweight composite substrates with potential applications in aerospace thermal management.