Calculation of Glass-Forming Ability in the Ni-Zr and Ni-Ti Systems from Interatomic Potentials

摘要

For the Ni-Zr and Ni-Ti systems, Molecular-dynamics (MD) simulations are conducted to compare the relative stability of the terminal solid solutions versus the corresponding amorphous states as a function of solute concentrations. It turns out that the terminal solid solutions transform into an amorphous state spontaneously when the solute concentrations are beyond the maximum allowable values, i.e. the critical solubilities, determined to be 14 at.% Zr in Ni and 25 at.% Ni in Zr for Ni-Zr system and 38 at.% Ti in Ni and 15 at.% Ni in Ti for the Ni-Ti system, respectively. The glass-forming ranges are therefore deduced to be within the respective critical solubilities, i.e. 14-75 at.% Zr and 38-85 at.% Ti for the Ni-Zr and Ni-Ti systems, respectively, which are compatible with those from experiments and/or from the generalized Lindemann criterion. Moreover, MD simulation also reveals that solid-state amorphization does take place and that the growth of the amorphous interlayer follows exactly a t~(112) law. Besides, a solubility criterion is proposed that the lower the maximum solid solubility the less stable is the lattice of the metal upon solid-state reaction and it can explain the fact that the growing speed of amorphous interlayer toward Ni (melting point = 1528 K) is greater than that directed to the Zr (2128 K) lattice, while it is smaller than that to Ti (1941 K) side.