Glass-forming ability of elemental zirconium

Abstract

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 five-fold 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 K/s compatible with modern experiments.

The intimate relationship between structural relaxation and the energy landscape of monatomic liquid metals

“…All observations suggest that the solidification process in liquid aluminium starts already around this temperature deep inside the equilibrium liquid state, and the similarity with other liquid metals points to an universal dynamic crossover in liquid dynamics. That temperature was also seen for pure Zr 43 . Given the generality of the potential energy landscape concept on which the observed phenomenon is based, it could extend to other metals and alloys, which remains to be investigated.…”

Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations

“…The nucleation temperature of Zr glassy phase occurred at T g = 1000 K during the first cooling as shown in Figure 6 by [ 79 ] and predicted in Chapter 7. A second melting temperature at T n+ = 2378 K instead of T m = 2125 K was obtained during heating after quenching the liquid below T g and applying a mean heating rate R = +10 12 K/s.…”

“…This temperature is observed with high heating rates after the formation of glass and glacial phases at lower temperatures. A residual exothermic latent heat is still observed in some glass-forming melts with heating rates R + equal to 0.33–0.66 K/s [ 53 , 54 , 62 , 63 ] while R + ≅ 10 12 –10 13 K/s in liquid elements leads to full melting at T n+ [ 45 , 78 , 79 ]. The crystallization entropy is expected to be equal to S m / (1 + θ n+ ) and the crystallization enthalpy H m / (1 + θ n+ ) after the formation of glacial phases inducing early crystallization at lower cooling rates.…”

“…Equations (4)–(8) are applied at a second melting temperature with θ g = θ n+ for several elements as shown in Table 2 . The θ n+ values are experimental values applying high heating rates in MD simulations [ 45 , 78 , 79 ] or observing early crystallization during droplet free fall [ 80 ] or under high magnetic field [ 81 ]. The reduced temperature θ g = θ n+ is the highest glass transition temperature in a liquid having a reduced melting temperature equal to θ n+ .…”

“…Zr MD simulations during various quenching processes revealed two T g values 1000 K and 890 K and a full melting at 2378 K [ 79 ]. The same singular coefficient −0.11896 leads to T nG = 1258 and 1072 K as shown Lines 7 and 9 in Table 4 and full melting occurs at T n+ = 2378 K. For T g = 1000 K (Line 8), T nG can also be equal to 1184 K with an enthalpy coefficient of −0.14009 and T n+ = 2423 K. For T g = T m (Lines 5 and 6), the two singular coefficients would be −0.11895 and −0.14009 with T nG = 1661 and 1622 K leading to full melting at T n+ = 2378 and 2423 K, respectively.…”