Black ceramic coatings on Ti alloy with enhanced high absorptivity and high emissivity by plasma electrolytic oxidation

Abstract

A black ceramic coating with high absorptivity and emissivity was successfully prepared on TA7 (Ti‐5Al‐2.5Sn) in a hybrid electrolyte solution by plasma electrolytic oxidation for improving the imaging precision of optical system. The influence of electrolyte components and technical parameters on the composition, structure, and optical properties was investigated. The results show the coatings with typically porous structure are mainly composed of O, P, Si, Ti, V, Fe, and Ni. The corresponding amorhous oxide in the outer layer endows the coating with strong absorption in the visible light and infrared areas, and the crystallized TiO2 indwelling the inner layer contributes to the strong UV absorption property. In addition, the micropores of the coatings have different size ranges corresponding to the wavelengths, facilitating the increase of absorptivity and emissivity in some degree. The absorptivity and emissivity can be adjusted by electrolyte components and technical parameters. The coating presents the best absorptivity of 0.962 and emissivity of 0.950 in the electrolyte solution of 3 g/L NH4VO3, 5 g/L FeSO4, and 5 g/L C4H6O4Ni under 400 V for 10 minutes.

Black PEO Coatings on Titanium and Titanium Alloys Produced at Low Current Densities

“…The blackness of the coatings is affected by anions such as VO 3− , WO 2− 4 , MoO 2− 4 and transition metal cations such as Fe 2+ , Fe 3+ , Cu 2+ , Co 2+ , Ni 2+ and Zr 4+ , according to the literature [19,26,34]. Regarding our present study, additives based on molybdenum and iron were used.…”

“…Absorptance (α) was determined from the reflectance spectra of the coatings, according to Equation (1) (see Methods). The lower the reflectance is, the better the absorptance is [34]. Based on the spectra in Figure 2, all prepared coatings reflect almost 10% of light in the visible range, with a maximum reflectance in the NIR range of about 35%.…”

“…Here, R(λ) represents the spectral reflectance of the sample at a given wavelength λ, while I sol (λ) refers to the incident spectrum [34,44].…”

“…The critical elements of electrolytes used for the development of PEO black optical coatings fall into two broad groups: anions like VO 3− , WO 2− 4 , MoO 2− 4 , and transition metal cations, including Fe 2+ , Cu 2+ , Co 2+ , Ni 2+ and Zr 4+ [19,26,34].…”

Investigation of Stray Radiation Suppression in Infrared Imaging System Using a Novel Broadband and High-Absorption Ceramic Coating

“…The surface absorption performance of ceramic coating is directly related to coating thickness, surface roughness, material microstructure, and composition. Previous studies have shown that these parameters are mainly affected by the power mode, electrolyte composition, power parameters, and oxidation time of PEO technology [36][37][38]. Therefore, the above factors affecting the surface absorption properties of ceramic coatings were investigated in this paper.…”