Titanium anodization using pulsed ASD technique: effects on surface porosity, crystallinity and corrosion resistance of the film

Anodic spark deposition allows to obtain an oxide with a thickness at least two orders of magnitude larger than the one obtained with standard anodization at voltage lower than 80 V. The ASD treatment allows to increase considerably the corrosion resistance of titanium in aggressive environments. However, micro-arks developed during the film growth, induce the formation of porosity. In order to obtain a less porous surface, a new anodization technique was investigated using high cell voltage (larger than 120 V) but applying a pulsed signal with frequencies in between 20 Hz and 1000 Hz constructing different duty cycle values, where for duty cycle was considered the fraction of time during which anodic polarization was applied. Process parameters were optimized in order to obtain the lower porosity, the better corrosion resistance and an optimum degree of crystallinity, keeping an energy efficiency larger than the one obtained using a direct current method.