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 Al(70)Pd(25)Co(5) and Al(74)Pd(12)Co(14) 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 Al(74)Pd(12)Co(14) alloy was composed of structurally complex ε(n) phase, while the Al(70)Pd(25)Co(5) alloy was composed of ε(n) 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 Al(70)Pd(25)Co(5) alloy have been observed, indicating individual breakdown and re-passivation events on the sample surface. A preferential corrosion attack of ε(n) was found, while the binary δ phase (Al(3)Pd(2)) remained free of corrosion. A de-alloying of Al from ε(n) and formation of intermittent interpenetrating channel networks occurred in both alloys. The corrosion behavior of ε(n) is discussed in terms of its chemical composition and crystal structure. The corrosion activity of ε(n) could be further exploited in preparation of porous Pd–Co networks with possible catalytic activity.