The Study Of The Structure And Property Of The Fe-based Amorphous Alloys By First-principle Simulation

In this thesis we study the liquid and amorphous structure, and magnetic properties of Fe-based amorphous alloys through the first-principle molecular dynamic simulation. The work of this thesis includes the following two parts:In the first part, in order to understand the effects of the metalloid elements M(M: P, C, B) on the atomic structure, glass formation ability(GFA) and magnetic properties of Fe-based amorphous alloys, Fe80P13C7, Fe80P14B6 and Fe80B14C6 amorphous alloys are chosen to study through first-principle simulations. We compared the structure characteristic and magnetic properties of 1600 K and 300 K. The results indicate that Fe80P13C7 and Fe80P14B6 alloys have the larger Fe-Fe bond length than Fe80B14C6 alloy and the length of Fe-Fe bond in Fe80P13C7 and Fe80P14B6 alloys also increase more than that in Fe80B14C6 alloy as the decrease of temperature. The strength of Fe-P and Fe-C bond is stronger than the Fe-C bond, and the B-B, B-C atoms show the poor solute-solute avoidance. Additionally, according to the results of P-centered VPs, P atoms of Fe80P13C7 alloy exist in the different positions which induce the structure complexity of melts. Based on the above discussion, we speculate that the GFA of the three alloys are dropped in the order of Fe80P13C7, Fe80P14B6 and Fe80B14C6. To further verify the validity of simulation results, we do the DSC test of the three amorphous alloy ribbons and get the criterion of glass forming ability which is consistent with our speculation based on the simulation calculation. The magnetization of the three Fe-based amorphous alloys increases in the order of Fe80B14C6, Fe80P14B6 and Fe80P13C7 in the simulation. The metalloid elements(P, B and C) have the similar magnetic moment in the three Fe-based amorphous alloys, in which B has the largest negative magnetic moment of-0.12 μB followed by C about-0.11 μB and P contributes to a minimum negative magnetic moment about-0.06 μB.In the second part, Fe80-xCoxP13C7(x=5, 10, 15, 20 at.%) alloys are chosen to study through the first-principle molecular dynamic simulation in order to investigate the effects of the Co addition on the atomic structure and magnetic properties of this ally system. Additionally, we change the cooling rate in the simulation calculation to investigate the effects of cooling rate on the structure and magnetic properties of the present FeCoPC amorphous alloys. The simulation results indicate that the pair distribution functions(PDFs) and Voronoi polyhedra are basically similar in the alloy systems. The Fe75Co5P13C7 amorphous alloy has a larger increase in Fe-Fe bond and exhibits a more complicated structure and Coordination Number. Thus we propose that Fe75Co5P13C7 amorphous alloy has better glass forming ability among this series of alloys. The total magnetic moment of this series of alloys decreases with the increase of the Co content and the cooling rate.