The effect of pressure upon crystallization of rapidly supercooled Zirconium melts
Molecular dynamics simulations have been performed to explore the effect of pressure (P) on the crystallization of Zirconium (Zr) under rapid cooling. The structural evolutions have been analysed in terms of the system energy, the pair distribution function and the largest standard cluster analysis. It is found that at the cooling rate of 1.0×1011 K/s that can crystallize Zr melts into hcp crystals via the bcc intermediate state under zero pressure, the critical pressure (Pc) for vitrification is about 28.75 GPa; and the bigger the pressure, the higher the glass transition temperature Tg. At P<PC the Ostwald’s step rule is applied to Zr melts. Crystallization of rapidly super-cooled Zr melts under pressures always begins with bcc phase and ends in hcp crystal; and the higher the pressure, the lower the onset temperature (Tc) of crystallization. Different from the singleintermediate- state crystallization (SisC) under zero pressure, multiple-intermediate-state crystallization (MisC) is usually observed under pressures. Structural analysis reveals that if nucleation is essential completed at the end of the first crystalline (bcc-dominated) stage, MisC will occurs; otherwise SisC. The origination of such observation is also discussed from the effect of pressure upon the thermodynamics and kinetics factors. These findings are useful for comprehensively understanding the solidification of metals under pressures.