Corrosion behavior of Al-Cu-Fe quasicrystals

For any application of quasicrystals or quasicrystalline coatings, e.g. for extruders, turbine blades or frying pans, corrosion resistance is of utmost importance. Therefore, corrosion of the quasicrystalline as well as related crystalline phases in the system Al-Cu-Fe was studied in particular at intermediate pH values in order to clarify the influence of the quasicrystalline structure. Salt spray tests were performed at 35°C with several single phase materials in the Al-Cu-Fe system. Highest corrosion resistance was observed in crystalline aluminides AlFe as well as Al5Fe2 where a protective oxide film had developed. The quasicrystalline alloy as well as crystalline Al7Cu2Fe exhibit severe corrosion accompanied with the formation of Cu, Cu2O and Al(OH)3. Anodic polarization of Al63Cu25Fe12 icosahedral quasicrystals reveal after a potentiodynamic scan in 0.1N NaOH the formation of an oxide layer consisting of FeO and Cu2O; there is only very little evidence for a phase transformation of the quasicrystal due to Al loss by selective corrosion. During further polarization in the passive region the oxide layer was observed to transform into probably higher oxidized states. The overall thickness of the oxide layer depends on the scan time, however, not on further polarization time at a distinct potential.