Corrosion behaviour of quasicrystal Al – Cu – Fe and Al – Ni – Fe alloys in acidic solutions

Abstract

Due to unique physical and mechanical properties of quasicrystals, the Al – Cu – Fe and Al – Ni – Fe alloys can be applied as coatings for parts working under friction, abrasive wear etc. During the performance most of the coatings are affected by corrosion which makes it necessary to study their behavior in acidic solutions. Structure of the Al – Cu – Fe and Al – Ni – Fe alloys has been investigated by methods of quantitative metallographic, X-ray fluorescent, X-ray analyses. Corrosion behavior of the alloys has been explored at 20±2 °С by gravimetric method in HCl, H₂SO₄, HNO₃, H₃PO₄ acidic solutions (pH=1.0) during 1 – 4 hours. pH of corrosion media has been controlled by ionometer EB–74. The samples surface exposed to acidic solutions has been investigated by scanning electron microscopy. The structure of the Al₆₃Cu₂₅Fe₁₂, Al₇₂Fe₁₅Ni₁₃ and Al_71.6Ni₂₃Fe_5.4 alloys constituted of quasicrystalline phases differing in type, respectively icosahedral γ-phase and decagonal D-phase, has been investigated. After 4 testing hours, the maximal mass loss of the Al₆₃Cu₂₅Fe₁₂ alloy has been established to occur in sulphuric acid and minimal mass loss – in ortophosphoric acid. For the Al₇₂Fe₁₅Ni₁₃ alloy, maximal mass loss is observed in sulphuric acidic solution and for the Al₇₂Fe₁₅Ni₁₃ alloy – in ortophosphoric acidic solution. Both the alloys do not practically corrode in hydrochloric and nitric acids. The Al – Ni – Fe alloys show higher resistance to corrosion compared with that of the Al – Cu – Fe alloy. The surface of the Al – Ni – Fe alloys dissolves in acidic media more homogeneously as against the surface of the Al – Cu – Fe alloy. The corrosion behavior of the quasicrystal Al – Cu – Fe and Al – Ni – Fe alloys has been compared in HCl, H₂SO₄, HNO₃, H₃PO₄acidic solutions with the same pH=1.0. The mass loss per unit area of the samples versus alloy composition and corrosion time in acidic solutions has been determined. The results of corrosion tests have been explained considering the investigations of surface structure change of the samples exposed to acidic solutions. The Al_71,6Ni₂₃Fe_5,4 alloy that shows the highest resistance to corrosion in acidic solutions has been recommended as coating to protect surface of aerospace parts working in acidic media.