Molecular dynamics simulation of nanoindentation of Fe3C and Fe4C

Saurav Goel,Suhas S Joshi,Gasser Abdelal,Anupam Agrawal

doi:10.1016/j.msea.2013.12.091

Abstract

Study of nanomechanical response of iron carbides is important because presence of iron carbides greatly influences the performance and longevity of steel components. This work contributes to the literature by exploring nanoindentation of Fe3C and tetrahedral-Fe4C using molecular dynamics simulation. The chemical interactions of iron and carbon were described through an analytical bond order inter-atomic potential (ABOP) energy function. The indentations were performed at an indentation speed of 50m/s and a repeat trial was performed at 5m/s. Load–displacement (P–h) curve for both these carbides showed residual indentation depth and maximum indentation depth (hf/hmax) ratio to be higher than 0.7 i.e. a circumstance where Oliver and Pharr method was not appropriate to be applied to evaluate the material properties. Alternate evaluation revealed Fe3C to be much harder than Fe4C. Gibbs free energy of formation and radial distribution function, coupled with state of the average local temperature and von Mises stresses indicate the formation of a new phase of iron-carbide. Formation of this newer phase was found to be due to deviatoric strain rather than the high temperature induced in the substrate during nanoindentation.

Highlights

Iron carbides are prime candidates for sensors, magnets, catalysts, and alternative raw materials used for steel production and for carbon nanotube growth by the pyrolysis of organometallic precursors [1]
Even though it is known that cementite influences the properties of steel during service life of the components at high pressures and temperatures such as in turbine blades and reactor vessels, its mechanical behaviour at a fundamental atomic level is not known [8]
This study aims to bridge this gap by examining the nanoindentation [18] behaviour of Fe3C and investigating if the reported macroscale experimental studies on compression behaviour of cementite can be extrapolated to nanoscale behaviour of cementite during nanoindentation

Summary

Introduction

Iron carbides are prime candidates for sensors, magnets, catalysts, and alternative raw materials used for steel production and for carbon nanotube growth by the pyrolysis of organometallic precursors [1]. Some of the major phases of iron carbide identified till date are shown, which highlights the constituents and arrangement of these phases and their respective mechanical properties. A scratch test showed that the track length of a groove made on pearlite phase was smaller than that made on the ferrite phase [6] This difference was attributed to the relative higher hardness of pearlite as it contains lamellar cementite (ten times harder than ferrite). An improved understanding of the nanomechanical response of cementite at nanoscale can help improve the design of newer class of steels

Objectives

Results

Conclusion