Effect of electrode potential on the tribocorrosion of tungsten

The tribocorrosion behavior of tungsten sliding against an alumina ball was evaluated in sulfuric acid under applied electrode potential. Surface chemistry of worn and unworn surfaces was evaluated using XPS and AES. Quasi-potentiostatic polarization curves and potential step measurements were performed under mass transport control to assess relevant corrosion factors. It was found that the tribocorrosion rate of tungsten varies with the applied electrode potential and goes through a maximum for a potential of 0.5 V MSE. Different material removal mechanisms were identified. In the wear track, materials deterioration proceeds by cyclic mechanical removal of the passive oxide film followed by anodic oxidation. The removal rate was found to be proportional to the passivation charge density determined in independent electrochemical experiments. At higher potential (1 V MSE) a thick WO3 tribolayer forms and by covering the wear track reduces the tribocorrosion damage. Outside the wear track the stirring of the solution induced by the moving alumina ball leads to an enhancement of the dissolution rate of the WO3 passive film and thus to higher material wastage.