Relationship between Phase Occurrence, Chemical Composition, and Corrosion Behavior of as-Solidified Al–Pd–Co Alloys

The microstructure, phase constitution, and corrosion performance of as-solidified Al70Pd25Co5 and Al74Pd12Co14 alloys (element concentrations in at.%) have been investigated in the present work. The alloys were prepared by arc-melting of Al, Pd, and Co lumps in argon. The Al74Pd12Co14 alloy was composed of structurally complex en phase, while the Al70Pd25Co5 alloy was composed of en and δ phases. The corrosion performance was studied by open circuit potential measurements and potentiodynamic polarization in aqueous NaCl solution (3.5 wt.%). Marked open circuit potential oscillations of the Al70Pd25Co5 alloy have been observed, indicating individual breakdown and re-passivation events on the sample surface. A preferential corrosion attack of en was found, while the binary δ phase (Al3Pd2) remained free of corrosion. A de-alloying of Al from en and formation of intermittent interpenetrating channel networks occurred in both alloys. The corrosion behavior of en is discussed in terms of its chemical composition and crystal structure. The corrosion activity of en could be further exploited in preparation of porous Pd–Co networks with possible catalytic activity.