Influences of current density on structure and corrosion resistance of ceramic coatings on Ti–6Al–4V alloy by micro-plasma oxidation

Abstract

Current density is a key factor during micro-plasma oxidation (MPO) process. Its influences on structure, morphology and corrosion resistance of ceramic coatings on Ti–6Al–4V by pulsed bi-polar micro-plasma oxidation in NaAlO 2 solution were studied in this paper. The ceramic coatings are composed of Al 2TiO 5, α-Al 2O 3 and rutile TiO 2, of which Al 2TiO 5 is the main crystalline. Compared with the condition of the same current density for both pulses, the rise of cathode current density led to an increase in the amount of rutile TiO 2, decreased the thickness and made the coatings compact; whereas the rise of anode current density led to an increase in the amount of α-Al 2O 3, increased the thickness and made the coatings coarse and porous. Whether increasing anode current density or cathode current density, there were more micro-holes on the surface of the coatings than that of same current density for both pulses. Besides, the corrosion resistance properties of the coated samples were better than that of Ti–6Al–4V substrate, whether considering the point corrosion resistance or the general corrosion resistance. When the anode current density ( I a) and the cathode current density ( I c) were both equal to 8 A/dm 2 ( I a/ I c=8/8 A/dm 2), or I a=8 A/dm 2 and I c=10 A/dm 2 ( I a/ I c=8/10 A/dm 2), the produced coatings had the best point corrosion resistance, and the latter was a little better than the former. When I a/ I c=10/8 A/dm 2, the produced coating's general corrosion resistance was best.