Structure And Corrosion of Quasicrystalline Cast Al–Co–Ni and Al–Fe–Ni Alloys in Aqueous NaCl Solution

Abstract

In this work the structure and corrosion behavior of quasicrystalline cast Al69Co21Ni10 and Al72Fe15Ni13 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 potentiodynamic method. Stationary potential values were measured by means of long-term registration of (Е,τ)–curves using ПІ–50–1 potentiostat and ПР–8 programmer with three-electrode electrolytic cell. A platinum electrode served as counter electrode and silver chloride – as reference electrode. The made investigations confirm the formation of stable quasicrystalline decagonal D-phase in the structure of Al69Co21Ni10 and Al72Fe15Ni13 alloys. In Al69Co21Ni10 alloy, at room temperature D-phase coexists with crystalline Al9(Co,Ni)2 phase, and in Al72Fe15Ni13 alloy – with Al5FeNi phase. Comparison of Vickers hardness of these phases exhibits the following sequence: H(D-AlCoNi)>H(D-AlFeNi)>H(Al5FeNi)>H(Al9(Co,Ni)2). In 5-% sodium chloride solution, the investigated alloys corrode under electrochemical mechanisms with oxygen depolarization. Compared with Al72Fe15Ni13 alloy, Al69Co21Ni10 alloy has more negative value of stationary potential (–0,40 V and –0,48 V, respectively), and its electrochemical passivity region extends due to the inhibition of anodic processes. For both alloys, transition to passive state in the saline solution is observed. A corrosion current density, calculated from (E,lgi)-curve, for Al69Co21Ni10 alloy amounts to 0.12 mА/сm2 and for Al72Fe15Ni13 alloy – to 0.14 mА/сm2. After immersion in the saline solution for 8 days, pits are revealed on the surface of the alloys in areas, mainly where the phase boundaries and flaws are located. The number and size of pits are smaller on the surface of Al69Co21Ni10 alloy as compared with those on the surface of Al72Fe15Ni13 alloy. The lower corrosion resistance of Al72Fe15Ni13 alloy may be explained by the presence of iron-containing phases in its structure. Based on obtained results, the Al69Co21Ni10 alloy has been recommended as coating material for rocket-and-space equipment working in marine climate.

Aqueous Corrosion of Aluminum-Transition Metal Alloys Composed of Structurally Complex Phases: A Review

“…It can be noted that Co substitution for Pd significantly improves the corrosion resistance of ε n . The positive influence of Co on the corrosion resistance of Al-TM alloys has also been observed by Sukhova and Polonskyy [108]. It is therefore the chemical composition and not the crystal structure of the phase that plays a dominant role in the corrosion resistance.…”

Effect of Structure and Cooling Rate on Mechanical Properties and Wear Resistance of Fe–В–С Alloys

“…Розвиток промислового виробництва (як в Україні, так і за її межами) постійно потребує використання стопів на основі заліза з підвищеними властивостями. Ключовим чинником формування необхідного комплексу характеристик є структурний фактор [1][2][3][4][5]. Морфологія та будова структурних складових ефективно впливають на механічні й експлуатаційні властивості [6][7][8][9][10].…”

“…3 К/с викликає структурні зміни, пов'язані зі зсувом ліній на діяграмі стану в бік залізного кута. Як наслідок, вміст первинної аустенітної фази в доевтектичних стопах збільшується, а борокарбіду Fe2(B,C) в заевтектичних стопах зменшується.…”

Surface Laser Melting of a Carburized LPBF-manufactured Ti-based Biomedical Grade Alloy

“…As follows from SEM observations, titanium oxycarbide has the same angular morphology which is characteristic of titanium carbide. The similarity in chemical composition, morphology, and crystal lattice suggests one assume that Ti(O1 − xCx) is close to TiC in physical-mechanical properties (including hardness) [26]. Therefore, the presence of the dispersed inclusions of titanium oxycarbide in the melted layer can explain its extremely high hardness (1000-1200 HV).…”