Development and Characterization of High Emittance and Low-Thickness Plasma Electrolytic Oxidation Coating on Ti6Al4V for Spacecraft Application

Plasma electrolytic oxidation (PEO) or microarc oxidation process has been carried out on Ti6Al4V substrate in electrolytic bath containing sodium silicate and sodium hypophosphate. The phase composition, microstructure and roughness of the PEO coating are examined by x-ray diffraction, scanning electron microscopy and profilometry techniques, respectively. Wavelength-dependent thermo-optical properties viz. solar absorptance ( α_s ) and IR emittance ( ε ir ) are recorded by UV-VIS-NIR and FTIR spectrophotometer, respectively. Nanomechanical properties such as nanohardness ( H ) and Young’s modulus ( E ) are evaluated by well-established nanoindentation technique. The PEO coating is found to be hydrophobic (contact angle 108°) and possesses low thickness of 5-9 m. Average ε ir is obtained to be 85