Peculiarities in structure formation and corrosion of cast quasicrystalline Al63Cu25Fe12 and Al63Co24Cu13 alloys in sodium chloride aqueous solution

O V Sukhova,V A Polonskyy

doi:10.15330/pcss.21.3.530-536

Abstract

In this work the structure and corrosion behavior of quasicrystalline cast Al63Cu25Fe12 and Al63Co24Cu13 alloys in 5-% sodium chloride solution (рН 6.9–7.1) were investigated. The alloys were cooled at 5 К/s. The structure of the samples was studied by methods of quantitative metallography, X-ray analysis, and scanning electron microscopy. Corrosion properties were determined by the potentiodynamic method. The made investigations confirm the formation of stable quasicrystalline icosahedral (y) and decagonal (D) phases in the structure of Al63Cu25Fe12 and Al63Co24Cu13 alloys correspondingly. In 5-% sodium chloride solution, the investigated alloys corrode under electrochemical mechanisms with oxygen depolarization. Compared with Al63Cu25Fe12 alloy, Al63Co24Cu13 alloy has a less negative value of free corrosion potential (–0.43 V and–0.66 V, respectively), and its electrochemical passivity region extends due to the inhibition of anodic processes. A corrosion current density, calculated from (E,lgi)-curve, for Al63Co24Cu13 alloy amounts to 0.18 mА/сm2 and for Al63Cu25Fe12 alloy – to 0.20 mА/сm2. The lower corrosion resistance of Al63Cu25Fe12 alloy may be explained by the presence of iron-containing phases in its structure. Based on obtained results, the Al63Co24Cu13 alloy was recommended as a coating material for rocket-and-space equipment working in a marine climate.

Highlights

The Al–Cu–Fe and Al–Cu–Co alloy systems containing stable quasicrystalline phases are the most interesting functional materials
Decagonal quasicrystals combine two types of crystalline order: they are quasiperiodic in a plane and they are periodic in the direction perpendicular to a plane
The Al63Cu25Fe12 and Al63Co24Cu13 alloys were prepared of high purity (99.99 %) components put in a graphite crucible and melted using Tamman furnace

Summary

Introduction

The Al–Cu–Fe and Al–Cu–Co alloy systems containing stable quasicrystalline phases are the most interesting functional materials. Three-dimensional Al–Cu–Fe quasicrystals show a five-fold symmetry and have icosahedral structure [1, 2]. The Al–Cu–Co quasicrystals are two-dimensional decagonal quasicrystals consisting of periodic stacking of atomic layers with a tenfold symmetry within the plane [3, 4]. Decagonal quasicrystals combine two types of crystalline order: they are quasiperiodic in a plane and they are periodic in the direction perpendicular to a plane. This property sets decagonal phases apart from periodic crystals, as well as from icosahedral quasicrystals

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Results

Conclusion