Silicate Spray-Coated Nickel-Plated Titanium Alloy for Space Applications: Corrosion Resistance and Thermo-optical Properties

Abstract

An inorganic silicate black spray coating (BSC) is employed on the blackened electroless nickel (ENB)-plated Ti-6Al-4V to enhance thermo-optical properties as well as corrosion resistance for use in spacecraft thermal control applications. The composite coating (BSC-coated ENB) is characterized with respect to impedance spectroscopy and potentiodynamic polarization to evaluate corrosion resistance. The results indicated that the corrosion resistance of the ENB specimen could be improved by post-spray coating due to reduction in porosity rate from 8.4 to 1.7. Further to ascertain the space worthiness of the composite coating, thermo-optical properties before and after the environmental tests (humidity, thermo-vacuum and thermal cycling tests) were measured. The composite coating showed a marked enhancement in solar absorptance (αs≥ 0.94) and infrared emittance (eIR≥0.84) values as compared to ENB specimen. Hence, the proposed composite coating demonstrated greater potential to be used in advanced thermal control applications in spacecraft where enhanced corrosion resistance and thermo-optical properties are essential.