Structure and Corrosion of Quasicrystalline Cast Alloys and Al-Cu-Fe Film Coatings

摘要

We study a quasicrystalline cast alloy and a film coating obtained by the improved method of threeelectrode ion-plasma sputtering of assembled targets with the following nominal composition: Al60Cu28Fe12 . The structure of the specimens was studied by the methods of quantitative metallography, X-ray diffraction analysis, X-ray energy-dispersive spectrometry, and transmission and scanning electron microscopies. The thermal stability of sputtered films was estimated with regard for the results of measurements of the electric resistance within the temperature range 293-1000 degrees K. The corrosion properties in a 5% aqueous solution of NaCl (pH 6.9-7.1) were determined by the potentiodynamic method. It was discovered that a quasicrystalline icosahedral i -phase in the structure of Al-Cu-Fe cast alloy coexists with lambda -Al13Fe4 , beta -AlFe(Cu), tau -AlCu(Fe), eta-AlCu, and theta-A(l2)Cu crystalline phases and occupies similar to 56% of the volume. The Al-Cu-Fe film coating contains a dispersed quasicrystalline i -phase similar to 3 nm in size, which is stable up to a temperature of 723 degrees K. The polarization experiments reveal a higher corrosion resistance of the Al-Cu-Fe film coating in salt solutions of sodium chloride as compared with the corrosion resistance of cast alloy. The corrosion process has the character of pitting and runs according to the electrochemical mechanism with oxygen depolarization.