Oxidation of Al-Cu-Fe and Al-Pd-Mn quasicrystals

Oxidation of Al-Cu-Fe and Al-Pd-Mn quasicrystals as compared to related crystalline phases was studied in air at high temperatures, Parabolic rate constants at 840 degreesC were about 6 x 10(-12) g(2) cm(-4) s(-1) for icosahedral Al-Cu-Fe, but only 3 x 10(-13) g(2) cm(-4) s(-1) for cubic AlFe. The oxide layer formed on the icosahedral alloy was inhomogeneous with respect to the oxide growth morphology. Oxide compositions were studied by Auger electron spectroscopy (AES) and X-ray induced photo electron spectroscopy (XPS). The theta -Al2O3 layer on Al-Cu-Fe did not contain any quantities of Cu or Fe that were significant according to the analyses by AES and XPS. In an advanced oxidation stage the theta -Al2O3 layer was penetrated by alpha -Al2O3 nodules, which contained about 5% CU. Oxidation of Al-Pd-Mn quasicrystals was found to be strongly influenced by evaporation of Mn. Whereas the formation of delta -Al2O3 was observed at 800 degreesC on Al-Pd-Mn quasicrystals followed by growth of needle-like theta -Al2O3, oxidation of hot isostatically pressed (HIPed) specimens at 850 degreesC led to the formation of a theta -Al2O3 layer containing also extremely thin areas. The metallic AI(LMM) Auger peak observed in these areas was four times the oxidic AI(LMM) peak. Neither in the thick nor the thin oxide areas were Pd or Mn observed. (C) 2000 Elsevier Science B.V. All rights reserved.