Electrochemical Dy-Alloying Behaviors of Ni-Based Alloys in Molten LiF–CaF₂–DyF₃: Effects of Constituent Elements

Abstract

The electrochemical Dy-alloying behaviors of Ni–Cr and Ni–Mo alloys were compared with those of Ni–Cr–Mo alloy and pure Ni in a molten LiF–CaF₂–DyF₃ (0.30 mol%) system at 1123 K. The effects of chromium and molybdenum as constituent elements of the Ni-based alloys were investigated. Cyclic voltammetry and open-circuit potentiometry indicated the formations of Dy–Ni alloys for all the Ni-based electrodes, as well as for the pure Ni electrode. XRD analysis confirmed the formation of DyNi₂ and DyNi₃ phases for all the electrodes electrolyzed at 0.20 V (vs. Li⁺/Li) for 60 min. SEM/TEM-EDX analysis of the sample prepared from Ni–Cr–Mo alloy revealed that the Dy-alloyed layer consists of Cr-rich Cr–Mo and Mo-rich Mo–Cr phases, as well as a Dy–Ni(–Fe) matrix phase. The shear stress measurements of the Dy-alloyed samples showed that the Ni–Cr–Mo alloy is the most suitable substrate to improve mechanical strength, which is explained by precipitation strengthening by both the Cr–Mo and Mo–Cr phases.

Fig. 8 Shear stress of the samples prepared by potentiostatic electrolysis of (a) Ni–Cr–Mo, (b) Ni–Cr, and (c) Ni–Mo plate electrodes at 0.20 V for 60 min in molten LiF–CaF₂–DyF₃ (0.30 mol%) at 1123 K. (d) The sample from the Ni plate was prepared at 0.20 V for 25–40 min in the same melt. Error bars represent their standard variations.