Pressure Effects on the Structural Evolution of Monatomic Metallic Liquid Hafnium

Abstract

Structural evolution of monatomic metallic liquid hafnium under high pressures of 0-50 GPa has been investigated by molecular dynamics (MD) simulations using the tight-binding many body potentials during rapidly solidified processes. The structural evolution and glass formation process have been analyzed by using pair distribution functions (PDF), Wendt-Abraham (RWA) parameter, Honeycutt-Andersen (HA) and Voronoi tessellation (VT) methods. When the system has been cooled with a cooling rate of 2x1013 Ks-1, the glassy states are obtained for P≤40 GPa pressures and the crystalline phase is obtained at P=50 GPa pressure. The number of face-centered cubic (fcc) and hexagonal close-packed (hcp) (fcc + hcp) type bonded pairs increase dramatically, while the number of perfect icosahedra, distorted icosahedra and body-centered cubic (bcc) type bonded pairs decreases with increasing of pressure. This is an indication that the solidification process of the system begins with nucleation in the liquid and that nucleation growth with increasing pressure continues to develop. The results show that the variation of local atomic bonded pairs is of great importance to understand the glass formation and crystallization process. However, it has been observed that the applied high pressure weakened icosahedral order and increased the fraction of other clusters in glassy hafnium at low temperatures. Furthermore, it has been observed that all glass transition temperatures (Tg), main bond types and main base clusters change with increasing pressure.