Change of Energy of the Cubic Subnanocluster of Iron Under Influence of Interstitial and Substitutional Atoms.

Anatoliy V Nedolya,Natalya V Bondarenko

doi:10.1186/s11671-016-1239-6

Abstract

Energy change of an iron face-centred cubic subnanocluster was evaluated using molecular mechanics method depending on the position of a carbon interstitial atom and substitutional atoms of nickel. Calculations of all possible positions of impurity atoms show that the energy change of the system are discrete and at certain positions of the atoms are close to continuous.In terms of energy, when all impurity atoms are on the same edge of an atomic cluster, their positions are more advantageous. The presence of nickel atoms on the edge of a cubic cluster resulted in decrease of potential barrier for a carbon atom and decrease in energy in the whole cluster. A similar drift of a carbon atom from central octahedral interstitial site to the surface in the direction <011> occurred under the influence of surface factors.Such configuration corresponds to decreasing symmetry and increasing the number of possible energy states of a subnanocluster, and it corresponds to the condition of spontaneous crystallization process in an isolated system.Taking into account accidental positions of the nickel atom in the iron cluster, such behaviour of the carbon atom can explain the mechanism of growth of a new phase and formation of new clusters in the presence of other kind of atoms because of surface influence.

Highlights

As is generally known, a new phase grows from a nucleation centre formed in local volume and has interface [1,2,3,4,5,6]
The estimations of energy changes of subnanocluster were based on three criteria when changing the position of the carbon atom from the central octahedral interstice in the direction of type to the unfinished surface octahedral site (SIS), which is on the surface and in the middle of the cube edge: Δ1 1⁄4 uPB– uCIS; jΔ2j 1⁄4 uSIS– uCIS; ð7Þ
JΔ3j 1⁄4 uSIS– uPB 1⁄4 Δ1 þ jΔ2j; where Δ1 is the specific barrier potential, Δ2 is the gain in cluster energy under influence of the surface, Δ3 is the specific changes of cluster energy between the positions of the carbon atom on the potential barrier and on the surface, uCIS is the cluster’s specific energy in case when the carbon atom is in the central octahedral interstitial site, uPB is the cluster’s specific energy when the carbon atom is on the maximum of potential barrier, uSIS is the cluster’s specific energy in case when the carbon atom is on the surface, in the unfinished octahedral interstitial site

Summary

Introduction

A new phase grows from a nucleation centre formed in local volume and has interface [1,2,3,4,5,6]. A precondition for the formation of a nucleus may be supersaturation as well as local physical changes related, for example, to the presence of soluble elements or atoms of another kind [7, 8]. Note that crystal formation is possible without large supersaturation, for example, as a result of physical changes in the local volume caused by the presence of soluble elements because of nano- and microsegregation [9, 10] owing to a concentration gradients during the accelerated crystallization. The changes in the surroundings where the crystalline phase is created are related to the phenomenon of mass transfer [25]. The rate of mass transfer depends on the properties of atoms, the property of crystalline environment, external factors, etc

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Results

Conclusion