Effect of Current Density on the Internal Stress Evolution during Galvanostatic Ti Thin Film Anodizing

A high resolution curvature measurement technique was used for investigating in situ the internal stresses developing during galvanostatic anodization of titanium thin films. The titanium electrodes were anodized in a 0.1 M H(3)PO(4) electrolyte, with current densities ranging from 0.5 to 4.1 mA/cm(2). Two distinct stages were observed in the evolution of the cell voltage with time: a first, low efficiency growth stage and a second near 100% efficiency growth stage. The transition between both stages systematically occurred at 6.0 V, independent of current density. In terms of internal stresses, these two stages correspond to two distinct regimes as well. In the first stage, compressive internal stresses were observed on the order of several gigapascals, which increased with decreasing current density. In the second stage, a tensile instantaneous stress component was found with an average value of 237 MPa, independent of current density. For the first stage, oxygen evolution inside the oxide film was responsible for both the low efficiency growth and the large compressive stresses. The tensile instantaneous stress evolution in the second stage was rationalized in terms of the rate of net free volume generation at the metal/oxide interface.