High‐performance infrared emissivity of micro‐arc oxidation coatings formed on titanium alloy for aerospace applications

Abstract Aerospace vehicles are subjected to high temperatures because of surrounding aerodynamic drag and the formation of large temperature gradients across the external structural parts of their airframe. To protect the vehicles, high‐infrared emissivity coatings that can radiate a large amount of heat into outer space are in demand. In this work, we describe the development and characterization of high emissivity ceramic coatings formed on a TC4 alloy surface by micro‐arc oxidation. We evaluate, in particular, the influence of NiSO ₄ concentration on current‐time response, the thickness, surface roughness, morphologies, bonding strength, and emissivity of these coatings. The results indicate that by increasing the NiSO ₄ concentration in electrolytes, the thickness and surface roughness of the coatings increase. The bonding strength becomes smaller with increasing concentration of NiSO ₄ , but is still maintains a value higher 30 MPa. The coatings possess good thermal shock resistance after being subjected to severe thermal shocks for 50 cycles, and no peeling of the coating is observed. A higher concentration of NiSO ₄ in electrolytes also leads to an increasing percentage of the nickel components in the coating to form a NiO phase, which enhances the emissivity of the coatings in the wavelength range of 3‐8 μm.