https://doi.org/10.1140/epjs/s11734-025-01843-1
Regular Article
Dual electrolyte plasma electrolytic oxidation coatings on Ti6Al4V for enhanced flat absorber properties in astronomical and scientific space missions
1
Thermal Systems Group, U. R. Rao Satellite Centre, Indian Space Research Organisation, 560017, Bengaluru, India
2
Department of Chemistry, Dayananda Sagar College of Engineering, 560078, Bengaluru, India
3
SRSPS, Liquid Propulsion Systems Centre, Indian Space Research Organisation, 560008, Bengaluru, India
a
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Received:
9
March
2025
Accepted:
31
July
2025
Published online:
20
August
2025
In astronomical and scientific missions, flat absorber surfaces that appear black are essential for optical benches and mounts, which are made from Ti6Al4V alloy for strength and reliability. However, the bare alloy does not meet the requirements for a flat absorber. This study developed oxide coatings with high infrared emittance and solar absorptance on Ti6Al4V using plasma electrolytic oxidation (PEO) with a dual electrolytic bath of sodium silicate (SS) and sodium polyphosphate (SPP), varying parameters like current density, potential difference, and duration. The coating was thoroughly characterized for coating thickness and roughness through X-ray diffraction (XRD), scanning electron microscopy (SEM), and profilometry techniques. Wettability of the PEO coatings was studied by water contact angle (WCA) measurement technique. Thermo-optical properties, including solar absorptance (200–2500 nm) and IR emittance (3–30 μm) of the PEO coatings, were measured using a solar reflectometer and an IR emissometer, respectively. Presently developed PEO coatings showed solar absorptance within the range 0.7–0.75 while the IR emittance was recorded as 0.84–0.89. The evaluation of nanomechanical properties, such as nanohardness and modulus of PEO coatings, was investigated using nanoindentation technique, demonstrating their mechanical integrity. Weibull statistical technique was employed to tackle high scatter in nanoindentation-induced data and predict the characteristic hardness and characteristic modulus of the PEO coatings. Nanohardness was found to be 3–5 GPa, while modulus was 57–88 GPa. Finally, to assess the corrosion resistance of the PEO coatings, potentiodynamic polarization behavior is also studied.
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Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
