Effects of pH of Electrolyte on Ceramic Micro-arc Oxidation Coating on Titanium Alloy

A titanium dioxide ceramic film was prepared on titanium alloy surface by micro-arc oxidation(MAO) in electrolyte of different pH. The surface morphology and film composition were studied by scanning electron microscopy and X ray diffractometer, and the relation among of electrolyte pH and current density, surface morphology of film and atom fraction of Ca and P were studied. The way of Ca, P elements getting into film being changed by electrolyte pH was also studied. The results show that a porous ceramic film containing calcium and phosphate was acquired. The current density first increased and then decreased with the increase of the oxidation time, and it increased with the increase of the electrolyte pH at the same time. The atom fraction of calcium in the film increased as the electrolyte pH increasing, however the atom fraction of phosphate decreased first and then increased. Calcium was mainly through high temperature sintering during micro-arc oxidation process into the film, but the phosphate element was through the static electricity and high temperature sintering working together.