Evaluation of the Glass-Forming Ability of Nb-Ni-Ti-Zr Quaternary Alloys Using the CALPHAD Approach

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The glass-forming ability of Nb-Ni-Ti-Zr quaternary alloys has been evaluated by combining the Calculation of Phase Diagrams method with the Davies-Uhlmann kinetic approach. Time-temperature-transformation (TTT) curves were obtained for steady state nucleation for the calculations, which give the time required for the formation of detectable amounts of a crystalline phase from a supercooled liquid as a function of temperature. Then, the critical cooling rates for glass formation were calculated from the TTT curves. Among the input parameters for the calculation of the TTT curves, the driving force for crystallization of the crystalline phase was derived using the thermodynamic function of each phase formulated in previous studies. The calculations show that the critical cooling rates for Nb_40−x−yNi₆₀Ti_xZr_y alloys decrease with increasing Zr content up to 20 mol%Zr. In particular, the calculated values for the Nb₁₀Ni₆₀Ti₁₀Zr₂₀ and Nb₅Ni₆₀Ti₁₅Zr₂₀ alloys were around 10⁰ K/s.