High-emissivity composite-oxide fillers for high temperature stable aluminum‑chromium phosphate coating

The production of high-performance heat-dissipating coatings on large structures has attracted significant attention owing to the ever-rising requirements of hypersonic vehicles. Mixtures of Al₂O₃, Cr₂O₃, Fe₂O₃, and MnO₂ were sintered at various temperatures, and the composites obtained by sintering at 1323 and 1523 K were used as fillers for aluminum‑chromium phosphate based heat-dissipating coatings. The microstructures and compositions of the fillers and coatings were investigated by scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. Spectral emissivity and cyclic oxidation were performed up to 973 K for the coatings. The results showed that the aluminum‑chromium phosphate coating prepared with the filler sintered at 1323 K displayed the maximum spectral emissivity in the waveband 3–8 μm owing to the Mn_1.5Cr_1.5O₄ phase. Further sintering the filler at 1523 K decreased the emissivity of the aluminum‑chromium phosphate coatings. The effects of the sintered fillers on emissivity were analyzed. In addition, the oxidation resistances, phase structures and morphologies of the aluminum‑chromium phosphate coatings after cyclic oxidation at 973 K for 200 h were studied, indicating that the aluminum‑chromium phosphate coatings prepared with the composite oxide fillers could improve the oxidation resistance of Ti alloys.