Evaluation of glass forming ability in the Ni–Nb–Zr alloy system by the topological instability ( λ) criterion

Abstract

Ni-based bulk metallic glasses (BMGs) usually exhibit high thermal stability, excellent mechanical properties, and superior corrosion resistance. Glass forming ability (GFA), which determines the critical amorphous size, limits the application of Ni-based BMGs. In the present work, we studied the ternary Ni–Nb–Zr alloy system, which shows relatively high GFA and the presence of passive-film-forming elements Nb and Zr that are beneficial for corrosion resistance. The GFA of the Ni–Nb–Zr alloy system was evaluated by the topological instability, λ criterion, used to calculate the minimum topological instability maps which indicate the compositions where the topological instability reaches the maximum among the surrounding stable phases. Such criterion was also combined with the electronegativity difference among the elements (Δ e) in each particular composition, which it is assumed to be related to the formation enthalpy (Δ H) and glass stability of the corresponding alloy. The data from the literature for the maximum amorphous diameter were compared with the predictions of the topological λ criterion and with the combined criterion ( λ × Δ e). Five compositions of rapidly solidified alloy ribbons were produced: Ni 45.5Nb 23Zr 31.5, Ni 50Nb 28Zr 22, Ni 57Nb 17.5Zr 25.5, Ni 62Nb 33Zr 5, and Ni 79Nb 8.5Zr 12.5. Structures of the samples were examined by X-ray diffraction (XRD). Glass transition, crystallization and melting behavior were investigated by a differential scanning calorimeter (DSC). The combined criterion ( λ × Δ e) provided specific guidelines for locating high glass-forming alloys in the Ni–Nb–Zr alloy system.