Features of Phase Formation Processes in Amorphous Alloys of Fe–Zr System

Abstract

AbstractThe thermodynamic and ab initio molecular dynamic approaches have been applied to analyze the phase formation processes in amorphous alloys of Fe–Zr system. The thermodynamic calculations of the kinetics of the phase formation process of binary amorphous alloys of the Fe–Zr system with continuous slow heating and pulsed laser processing are carried out. It was shown that the processes of phase formation in the binary alloys of the Fe–Zr system take place in two stages: initially, there are processes of phase stratification on two amorphous phases according to the type of spinodal decomposition, then crystallization of each amorphous phase. 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. 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 theoretical confirmation of the possibility of a course of explosive crystallization during pulsed laser annealing in binary amorphous alloys of the Fe–Zr system at a temperature lower than 60 K for the temperature of the beginning of intensive crystallization 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 is 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 drastical changes of the electronic spectrum and rearrangement of atoms, which we assign to the first stage of the amorphous alloy crystallization.KeywordsAmorphous alloyRelative integral free gibbs’ energyVolume part of crystalline phaseCrystallization processExplosive crystallizationPulsed laser annealingElectronic structureAb initio molecule dynamic