Quasicrystalline Al–Cu–Fe alloys obtained by casting and in the form of film coatings have a unique combination of structure and properties. Cast alloys are characterized by a coarse-grained structure with an icosahedral phase surrounded by an aluminum matrix. Film coatings, in turn, demonstrate a finer-grained or amorphous structure, depending on the spraying conditions.
In this paper, a quasicrystalline alloy obtained by casting and a thin film coating formed by an improved ion-plasma sputtering method using a three-electrode system and targets with a given composition of Al60Cu28Fe12 are investigated. The structural characteristics of the samples were analyzed using quantitative metallography, X-ray diffraction, X-ray fluorescence analysis, and transmission and scanning electron microscopy. The thermal stability of the deposited films was estimated based on the electrical resistance data in the temperature range from 293 to 1000°K. The corrosion resistance in 5% aqueous NaCl solution (pH 6.9–7.1) was studied using potentiodynamic measurements.
It was revealed that in the structure of the cast Al–Cu–Fe alloy, the quasicrystalline icosahedral i-phase is present together with the crystalline phases λ-Al13Fe4, β-AlFe(Cu), τ-AlCu(Fe), η-AlCu and θ-Al2Cu, occupying approximately 56% of the volume. The Al–Cu–Fe film coating is characterized by the presence of a dispersed quasicrystalline i-phase with a size of about 3 nm, which remains stable up to a temperature of 723°K. The results of polarization measurements indicate an increased resistance to corrosion of the Al–Cu–Fe film coating in sodium chloride solutions compared to the cast alloy. The corrosion process is localized and develops according to the electrochemical mechanism with oxygen depolarization.
The corrosion resistance of these materials is determined by their structure and composition. The icosahedral phase has high chemical inertness, providing protection against corrosion. However, the presence of structural defects, such as grain boundaries and dislocations, can reduce corrosion resistance.
Studies have shown that Al–Cu–Fe film coatings exhibit higher corrosion resistance compared to cast alloys. This is due to their more homogeneous structure and the absence of large defects. Further studies are aimed at optimizing the structure and composition of quasi-crystalline alloys to increase their corrosion resistance in various aggressive environments.
Author: S. I. Ryabtsev, V. A. Polonsky, O. V. Sukhova
Institute: Oles Honchar Dnipro National University; National Academy of Sciences of Ukraine