Glass-forming ability of elemental zirconium

We report large-scale molecular dynamics simulations of the glass formation from the liquid phase and homogeneous nucleation phenomena of pure zirconium. For this purpose, we have built a modified embedded atom model potential in order to reproduce relevant structural, dynamic, and thermodynamic properties from ab initio and experimental data near the melting point. By means of liquid-solid interface simulations, we show that this potential provides a thermodynamic melting temperature and densities of the solid and liquid state in good agreement with experiments. Using melt-quenching simulations with one million atoms, we determine the glass transition from the temperature evolution of the inherent structure energy as well as the nose of the time-temperature-transformation curve located in the deep undercooling regime. We identify the local structural origin of the glass-forming ability as a competition between bcc and fivefold polytetrahedral structures that may represent an impediment of rapid homogeneous nucleation at such high undercoolings. This suggests the ability of single elemental zirconium to form a glass from the melt with cooling rates of at least ${10}^{12}\mathrm{K}/\mathrm{s}$, compatible with modern experiments.

Figure 1

Upper panel: snapshot of the liquid-solid (100) interface with $640\times 10\times 10$ shape; lower panel: snapshot of the liquid-solid (100) interface with $80\times 40\times 20$ shape.

Figure 2

(a) Pair-correlation functions at $T=2500$, 2200, and $1850\mathrm{K}$, from the MEAM potential, AIMD of the present work as well as from the previous one [30], and compared to the experiment [64]; (b) velocity-autocorrelation function at $T=2500\mathrm{K}$ from the MEAM potential, AIMD of the present work.

Figure 3

Enthalpy as a function of temperature for the solid and liquid branches (see the text for details). The red line marks the slope of the glassy states as a guide for the eyes for the crossover between the liquid and glassy regimes.

Figure 4

Inherent-structure energy as a function of temperature for the Bulk 3 system with $N=1024000$ (see the text). Open symbols correspond to the ISE of the perfect crystalline phases.

Figure 5

Temperature evolution of the abundance of CNA bonds during the melt quenching. The vertical yellow bar indicates the glass transition region.

Figure 6

Time-temperature-transformation curve for the Bulk 3 system with $N=1024000$ and the Bulk 2 system with $N=16000$ in the temperature range between $T=1400$ and $1000\mathrm{K}$ (see the text). Inset: potential energy as a function of time for all the temperatures in the same temperature range. For each temperature, the chosen curve corresponds to the simulation in which the crystallization event occurs at a time closest to the average nucleation time. Arrows indicate the location on the potential energy curve where $15\%$ and $40\%$ of the atoms have a full bcc structural environment. For all temperatures, $40\%$ corresponds roughly to half of the potential energy drop during crystallization and is taken as the measure of the nucleation time.

Figure 7

Snapshot of the simulations at the onset of nucleation at $T=1150\mathrm{K}$ with $15\%$ of the atoms having a bcc environment. Left panel: the Bulk 3 system with $N=1024000$; right panel: the Bulk 2 system with $N=16000$. Only atoms with a bcc environment are drawn.