Chemistry

Metallurgy

Materials science

Scanning electron microscope

Plasma electrolytic oxidation

Electrochemistry

Engineering

Composite material

Sodium fluoride

Diffractometer

Electrode

Fluoride

Coating

Sodium

Electrolyte

Dielectric spectroscopy

Sodium hydroxide

Sodium aluminate

Inorganic chemistry

Corrosion

Sodium silicate

Chemical engineering

Physical chemistry

Aluminium

Microstructure

Journal of Asian Ceramic Societies

In the present study, the plasma electrolytic oxidation method was used to form ceramic coatings on pure Ti substrates. For this purpose, five different aluminate-based electrolytes containing various sodium-based additives (sodium hydroxide, sodium phosphate, sodium silicate, sodium tetraborate and sodium fluoride) were used. The role of additives in the growth, macrostructure, surface and cross-sectional microstructure, phase composition and corrosion resistance of the coatings was evaluated. An X-ray diffractometer and scanning electron microscope were used to study the microstructure and phase composition of the coatings, respectively. The corrosion resistance of the coatings was investigated by applying electrochemical impedance spectroscopy and potentiodynamic polarization tests in a 3.5 wt. % NaCl solution. The results revealed that use of a sodium phosphate additive led to formation of a coating (4.33 µm thick) with the most suitable microstructure and highest corrosion resistance (4.36 × 106 Ω cm2), which was 53 times higher than that of uncoated Ti.

Influence of different sodium-based additives on corrosion resistance of PEO coatings on pure Ti