Film Formation via Plasma Electrolyte Oxidation of Ti and Ti-5Mo-4V-3Al Alloy in High Alkaline Solutions

Abstract

This work investigates the characteristics of oxide films formed on Ti and the Ti alloy through a plasma electrolyte oxidation (PEO) process in highly alkaline medium in the presence or absence of phosphate ions. The obtained coatings showed different characteristics when they formed in high alkaline phosphate solutions particularly was anatase for Ti and rutile/titanium phosphate for the Ti alloy layer. Films formed in aqueous solution without KOH caused a reduction in current density and also reduced the number of microarcs, while in electrolytes with high OH- concentration, the current was low and the density of sparks was significant.

Effect of SiO 3 2− /OH− on plasma electrolytic oxidation of Ti-5Mo-4V-3Al

“…As a first step, 1 to 3 min after switching d.c. power supply, until the breakdown of oxide film, the current shows linear raise with increasing voltage. At this point film thickness and therefore, electrical resistance of film varies slightly which is the result of passivity effect of the electrolyte (Yerokhin et al 2000;Asadi et al 2010). The situation which is shown in figure 1b is related to the more corrosive solutions than figure 1a where achieving passivation is much more difficult.…”

“…In more corrosive media the current increases faster with more fluctuations. According to Inho Han's report, increasing OH -ions in electrolyte causes decrease in potential of breakdown and sparking voltage (Han et al 2007;Asadi et al 2010). In the maximum current density, the film breaks down that indicates the discharging of sample's surface in a short time interval.…”

“…The break in voltage diagram and spark formation on anode surface happened at the same time. Whenever hydroxyl ions concentration was raised, the amount of spark also boosted (Asadi et al 2010). It is known that most of cell voltage (power) is consumed for overcoming the resistance of growing oxide film thus voltage-current pattern defines film growth.…”