Abstract
This work aims to achieve deep insight into the phenomenon of phase transformation upon rapid cooling in metal systems and reveal the physical meaning of scatter in the time taken to reach crystallization. The total number of pure metals considered in this work accounts for 14. Taking pure copper as an example, the correlation between phase selection of crystal or glass and cooling rate was investigated using molecular dynamic simulations. The obtained results demonstrate that there exists a cooling rate region of 6.3 × 1011–16.6 × 1011 K/s, in which crystalline fractions largely fluctuate along with cooling rates. Glass transformation in this cooling rate region is determined by atomic structure fluctuation, which is controlled by thermodynamic factors. According to the feature of bond-orientation order at different cooling rates, we propose two mechanisms of glass formation: (i) kinetic retardation of atom rearrangement or structural relaxation at a high cooling rate; and (ii) competition of icosahedral order against crystal order near the critical cooling rate.
Highlights
Liquid-to-glass transition was well established[10,11]
The cooling-rate dependence of such correlation is hardly involved in these theories, and the picture of phase transformation at critical point of phase selection is unclear
This could be related to the scatter of the onset time for nucleation in the process of isothermal annealing for metallic liquid systems, as reported by experimental measurements and theoretical predictions in literatures[14,15]
Summary
Liquid-to-glass transition was well established[10,11]. the cooling-rate dependence of such correlation is hardly involved in these theories, and the picture of phase transformation (glass or crystal) at critical point of phase selection is unclear. It has been pointed out that the stability of supercooled liquid against crystallization, which is associated with the structural heterogeneity level[12], is affected by the liquid’s thermal history Following this scenario, nucleation density is sensitive to the atomic structures in the as-prepared supercooled liquid[13], which yields different pathways of crystallization. How the coupling of structural fluctuation and arrest of dynamics determines the phase transformation in supercooled liquid is still open To address this issue, in the present work, we choose pure-element metal systems, including Cu, Ag, Au, Ni, Pd, Pt, Al, Pb, Fe, Mo, Ta, W, Ti, and Zr, to investigate the effect of structural fluctuation on phase transformation at cooling rates near the critical point, so that the compositional fluctuation factor can be eliminated. Due to the similar results and consistent conclusions from these pure-element metal systems, here we only present the results of copper
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