MECHANISMS OF PASSIVITY OF NONEQUILIBRIUM AL-W ALLOYS

Sputter-deposited Al-W alloys exhibit considerably enhanced resistance to pitting corrosion over a range of pHs extending from pH 0 to 9.6. Surface analysis showed that although very little oxidized W is found in the passive film at near-neutral pHs, at pH 3 there are comparable amounts of oxidized W and Al. A review of the different mechanisms proposed to explain the passivity of this class of alloys suggests that the pitting resistance of Al-W is likely to result from inhibition and repassivation of pits due to the stability of oxidized W in low-pH environments as described by the solute-rich interphase model (SRIM).