THE CORROSION BEHAVIOR OF SPUTTER-DEPOSITED AL-TI ALLOYS IN 1-N HCL

The corrosion behavior of sputter-deposited Al-Ti alloys over a wide range of alloy composition has been investigated by electrochemical measurements and solution analysis. Particular attention is paid to the effects of titanium addition and structural difference between sputter-deposited and conventionally processed alloys. Although they are initially passive due to the presence of an air-formed film, depassivation occurs by prolonged immersion in 1 N HCl open to air at 30-degrees-C. The time to depassivation of sputter-deposited alloys is significantly longer than that of the argon-arc melted counterparts and increases with alloy titanium content regardless of structural change. The alpha-Al phase formed by sputtering is supersaturated with titanium, and hence transition from the single alpha-Al phase to the amorphous phase with increasing alloy titanium content leads to no clear discrepancy in the continuous extension of the depassivation time. The titanium addition accelerates the hydrogen ion reduction reaction, and hence the open circuit corrosion rate of alloys containing 57 at% or less titanium is higher than that of aluminum metal. Immediately after immersion preferential dissolution of aluminum occurs very slowly, possibly from the outer layer of the air-formed film. Dissolution rates of aluminum and titanium gradually increase, and depassivation results in steady active dissolution according to the alloy composition.