Thermal and optical performance of Ag+TiN–TiN–Al2O3 multilayer coatings for infrared camouflage in aerospace applications

Ag+TiN–TiN–Al₂O₃ multilayer coatings were deposited on Si (100) substrates using multi-target magnetron sputtering. The effects of vacuum annealing at 300 °C, 400 °C, and 500 °C were investigated in terms of structural, morphological, and optical properties, including infrared emissivity. XRD analysis showed improved crystallinity up to 400 °C, while partial degradation occurred at 500 °C. FESEM revealed grain coarsening and surface densification with increasing temperature. Optical reflectance increased with annealing, and the bandgap widened to a maximum of 2.30 eV at 400 °C, followed by narrowing at 500 °C due to defect formation. FTIR-based analysis indicated a minimum emissivity of 0.102 in the 3–5 μm range at 400 °C. The results demonstrate that 400 °C is the optimal annealing temperature for achieving low emissivity, high structural order, and stable optical performance, making the coatings suitable for infrared stealth and thermal management in aerospace applications.