Interaction in the Ni–Sc–Zr Ternary Alloys Along the 77.8 at.% Ni Section. Electrochemical Properties of the Alloys

Abstract

The interaction of Sc₂Ni₇ and Zr₂Ni₇ compounds (with C2/m and P6₃/mmc crystal structures and congruent melting temperatures of 1270 and 1438°C) in the ternary Ni–Sc–Zr system was studied employing physicochemical analysis methods (metallography, X-ray diffraction, differential thermal analysis, and electron microprobe analysis). The section between the compounds was shown to be quasibinary of peritectic type, with peritectic points of 1340 ± 13°C and 14 at.% Sc. At the peritectic temperature, about 10 at.% Zr dissolves in the Sc₂Ni₇-based phase and about 8 at.% Sc in the Zr₂Ni₇-based phase. Electrochemical studies conducted through cathodic polarization of the ternary Sc₂Ni₇ and Zr₂Ni₇ alloys using a PI-50-1 potentiostat, with a three-electrode electrochemical cell consisting of a working ceramic anode, a platinum cathode, an electrolyte (a 3% NaCl aqueous solution), and a silver chloride Ag/AgCl/KCl reference electrode, did not reveal any tendency to hydrogenation in their solid solutions. The influence of preliminary cathodic reduction of the 77.8 at.% Ni–8 at.% Sc–Zr sample on its subsequent anodic dissolution was determined. The initial surface of the 77.8 at.% Ni–8 at.% Sc–Zr sample was found to be much more resistant to anodic oxidation than the surface preliminary subjected to cathodic reduction because of a significant decrease in its oxide component.