Formation and Thermal Stability of Ni-Based Bulk Metallic Glasses in Ni-Zr-Nb-Al System

Abstract

An Al element was selected as an alloying metal to improve the glass-forming ability (GFA) of Ni-Zr-Nb alloys. The thermal stability and glass-forming ability of Ni-Zr-Nb-Al alloys were investigated. It was found that the partial substitution of Nb by Al led to significant shift of the onset crystallization temperature T_x and the liquidus temperature T_l, while the glass transition temperature T_g was less composition sensitive. The supercooled liquid region, ΔT_x (=T_x−T_g), the reduced glass transition temperature (T_g⁄T_l) and γ=T_x⁄(T_g+T_l) increased with increasing Al content up to 5 at%. The best GFA was found at Ni₆₀Zr₂₀Nb₁₅Al₅ with a critical diameter of 3 mm. The characteristic parameters are: ΔT_x=54 K, T_g⁄T_l=0.615 and γ=0.405. The maximum values of ΔT_x and T_g⁄T_l were 72 K and 0.617, respectively, at Ni₆₀Zr₂₅Nb₁₀Al₅. The compression tests showed that the Ni₆₀Zr₂₀Nb₁₅Al₅ BMG possessed high fracture strength of 2900 MPa, Young’s modul of 152 GPa, and plastic elongation of 2.5% at room temperature.