Annealing study of amorphous bulk and nanoparticle iron using molecular dynamics simulation

Abstract

Annealing study of amorphous bulk and nanoparticle iron at temperatures from 500 K to 1000 K has been carried out using molecular dynamics (MD) simulations. The simulation is performed for models containing 104 particles Fe at both crystalline and amorphous states. We determine changes of the potential energy, pair radial distribution function (PRDF) and distribution of coordination number (DCN) as a function of annealing time. The calculation shows that the aging slightly reduces the potential energy of system. This result evidences that the amorphous sample undergoes different quasi-equilibrated states during annealing. Similar trend is observed for nanoparticles sample. When the samples are annealed at high temperatures we observe the crystallization in both bulk and nanoparticle. In particular, the system undergoes three stages. At first stage the relaxation proceeds slowly so that the energy of system slightly decreases and the samples structure remains amorphous. Within second stage a structural transformation occurs which significantly changes PRDF and DCN for the relatively short time. The energy of the system is dropped considerably and the amorphous structure transforms into the crystalline. Finally, the crystalline sample undergoes the slow relaxation which reduces the energy of system and eliminates structural defects in crystal lattices.

Influence of heating rate, temperature, pressure on the structure, and phase transition of amorphous Ni material: A molecular dynamics study

“…At the heating rate of 2 × 10 5 K/s, then amorphous Ni material has a cubic shape shown in yellow color ( Figure 1 a) with the dimension = 3.28 nm, the total energy E tot = -13138 eV, the average coordinate number CN = 13, and the first peak's position of the RDF r Ni-Ni = 2.45 Å, the first peak's height of the RDF g(r) = 4.53 ( Figure 1 b). With the Sutton-Chen dip interaction, our obtained Ni–Ni binding length is r Ni-Ni = 2.45 Å and this result is in good agreement with previously published results r Ni-Ni = 2.43 Å [ 73 ], r Ni-Ni = 2.45 Å [ 74 ], r Ni-Ni = 2.24 Å [ 66 ] and is twice than the covalent radius 1.21 Å [ 76 ]. When the heating speed increases from 2 × 10 5 K/s to 2 × 10 6 and 2 × 10 7 K/s, the coordination number CN is 13 and constant, the position r Ni-Ni is 2.45 Å and constant, the height g(r) increases from 4.53 to 5.27, the size decreases from 3.28 nm to 3.23 nm.…”

“…In particular, appears the difference between the Curie temperature and the glass transition temperature of the material and that is caused the dependence of these quantities on the density, the bonding length and the radial distribution function [ 68 , 69 , 70 , 71 , 72 ]. By the empirical method Ichikawa shows that the closest linking distance is 2.43 Å [ 73 ] for bulk Ni, 2.45 Å [ 74 ] for Ni nanoparticles and 2.24 Å [ 75 ] for AlNi nanoparticles. Meanwhile, Ni material has the covalent radius of 1.21 Å [ 76 ], which shows that the Ni–Ni bond length is twice the covalent radius.…”

Crystallization Pathway for Crystallization of FeB Nanoparticles

“…It is interesting that the simple potential proposed by Pak and Doyama long time ago, well describes thermodynamics and structure properties of Fe and Fe-alloys materials. MD simulations carried out by various researchers and using Pak-Doyama potential confirmed these points [27][28][29][30][31][32][33][34]. Therefore, in the present work, we conduct the MD simulation using Pak-Doyama type potentials to describe the interaction between atoms in NP samples.…”

“…To study the crystallization we have prepared 900-sample by heating the 300-sample to 900 K and then relaxing isothermally over 10 7 steps. To analyze the atomistic arrangement of Fe atoms in NP we determine the pair radial distribution function (PRDF) for Fe-Fe pair using the procedure reported in the previous work [27,34].…”

Study of Effect of Size on Iron Nanoparticle by Molecular Dynamics Simulation

“…Iron nanoparticle has many attractive properties and finds important applications in different areas of industry. So, the interest in this type material continues to grow in recent years [1][2][3]. NP can be produced either in amorphous or crystalline states.…”