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 them was shown to be quasibinary of peritectic type, with the peritectic temperature of 1340 ± 13 °C and peritectic composition of about 14 at.% Sc. At the peritectic temperature, about 10 at.% Zr dissolves in the Zr₂Ni₇-based phase and about 8 at.% Sc in the Zr₂Ni₇-based phase. Electrochemical studies performed by cathodic polarization of ternary Zr₂Ni₇- and Sc₂Ni₇-based alloys using a PI-50-1 potentiostat, whose three-electrode electrochemical cell consisted 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 a tendency to hydrogenation of their solid solutions. For the 77.8 at.% Ni–8 at.% Sc–Zr sample, the influence of the previous cathodic recovery 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 significantly more resistant to anodic oxidation than the surface that was previously restored during cathodic process because of a significant reduction in its oxide component.