Corrosion-resistant composite coatings reinforced by decagonal quasicrystals

Abstract

The structure and corrosion properties of quasicrystalline Al₆₅Co₂₀Cu₁₅ and Al₇₂Co₁₈Ni₁₀ reinforcement alloys and composite coatings on their basis produced by infiltration without applying pressure were studied. Copper-based L62 and BrOTs 10-2 alloys and aluminum-based AMg30 alloy were used as metal matrices in the composite coatings. The structural and phase composition of the reinforcement alloys and coatings was determined by metallography, scanning electron microscopy, energy-dispersive X-ray spectrometry, and X-ray diffraction. The corrosion properties were studied in aqueous solutions of HCl, H₂SO₄, HNO₃, and H₃PO₄ acids (рН = 1.0) for 1–4 h at room temperature. In the structure of the reinforcement alloys, a quasicrystalline decagonal D-phase was established to coexist with crystalline Al₄(Co, Cu)₃ and Al₃(Cu, Co)₂ phases in the Al₆₅Co₂₀Cu₁₅ alloys and Al₉(Co, Ni)₂ and Al(Co, Ni)₂ phases in the Al₇₂Co₁₈Ni₁₀ alloy. The corrosion tests in acid solutions indicated that the Al₆₅Co₂₀Cu₁₅ reinforcement alloy had higher corrosion resistance in the solutions of sulfuric and nitric acids, but the Al₇₂Co₁₈Ni₁₀ reinforcement alloy in the solutions of hydrochloric and phosphoric acids. During infiltration of the Al₆₅Co₂₀Cu₁₅ and Al₇₂Co₁₈Ni₁₀ reinforcement alloys, the molten copper-based L62 and BrOTs 10-2 matrices penetrate inside the reinforcement along the boundaries of the quasicrystalline D-phase through the preferential dissolution of crystalline phases of the reinforcement alloys. Unlike the copper-based alloys, the aluminum-based AMg30 matrix does not penetrate inside the reinforcement alloys, dissolving predominantly the crystalline phases located in the surface layers. The highest corrosion resistance in the acidic media is shown by the composite coatings with the BrOTs 10-2 matrix. The coatings with the AMg30 binder have the lowest corrosion resistance because of the formation of Al₃Mg₂ phase at the interfaces between the reinforcement alloy and solidified matrix.