Nanocomposites and nanomaterials

Features of phase-formation processes in amorphous alloys 
of  Fe-Zr system

Tsaregradskaya T.L.1, Plyushchay I.V.1, Kalenyk O.O.1, Plyushchay A.I.2, 
Saenko G.V.1

1 Taras Shevchenko National University of Kyiv, 64/13, Volodymyrska Street, 
City of Kyiv, 01601 Ukraine
E-mail: tsar_grd@ukr.net

2 G.V. Kurdyumov Institute of Metal Physics, N.A.S.U. Kyiv, 142 Ukraine

        The thermodynamic and ab initio molecular dynamic approaches have been applied to analize the phase-formation processes  in  amorphous alloys of Fe-Zr system. The laws of the kinetics of crystallization in the high-temperature region, which determine the possibility of obtaining alloys of the Fe-Zr system in the amorphous state, are considered. It was shown that the region of amorphization of binary alloys of the Fe-Zr system is within (3-15)% at. zirconium, which is well in agreement with experimental data. The calculations carried out within the framework of the modified theory of homogeneous nucleation for binary systems have shown that the process of crystallization of binary alloys of the Fe-Zr system with continuous slow heating is two-step: first, the solid solution Zr in α-Fe crystallizes, then the chemical compound Fe3Zr, with complete crystallization occurs in the temperature interval of 90 K. The calculations carried out have shown that explosive crystallization may occur in the pulsed laser annealing in binary amorphous alloys of the Fe-Zr system. The temperature at which explosive crystallization is possible due to the laser pulse was less than 60 K for the temperature of the beginning of intensive crystallisation at slow heating. 
First-principles molecular dynamics simulations of amorphization and crystallization process in the Fe-Zr system have been presented. The atomic positions in the Fe29Zr3 supercell were modeled by simulating annealing by the density functional theory in the generalized gradient approximation. Changes in the density of electronic states of the Fe29Zr3 supercell under liquid-amorphous-crystalline phase transitions are discussed. The most marked difference between the electronic spectrum of liquid and amorphous phases is a pseudogap at the Fermi level which consistent with the Nagel-Tauc electronic criterion of the amorphous metallic alloy thermal stability. Further simulating annealing in the Isothermal/isenthalpic ensemble under the higher temperatures leads to the drastically changes of the electronic spectrum and rearrangement of atoms, which we assign to the first stage of the amorphous alloy crystallization.