Quantification of ferrite-martensite interface in dual phase steels: A first-principles study

The ferrite-martensite interfacial energy and equilibrium interfacial length as a function of martensite carbon content are assessed using first-principles atomistic simulations. The weight percent of carbon in the martensite phase was implicitly varied from 0.6 to 1.8 wt percent by modifying the lattice constant of body-centered tetragonal (BCT) martensite according to Kurdjumov and Kaminsky's empirical expressions. With increasing carbon content, a decrease is found in both the interfacial energy and in the equilibrium distance between ferrite and martensite interfaces. Moreover, the Morse interatomic potentials between the atoms in the ferrite-martensite interface for four different martensite carbon contents are calculated, and the parameters of the Morse potential are correlated linearly with the martensite carbon content. In addition, the dissociation local strains during uniaxial loading in a direction normal to the interfacial plane are calculated from the interatomic potentials. The local strain at the interface needed for ferrite-martensite interface separation increases with increase in martensite carbon content. The fitted expressions can be used to predict the ferrite-martensite interfacial energy, equilibrium interfacial distance, dissociation local strain at the interface, and the Morse parameters as functions of martensite carbon content within the range of 0.6-1.8 wt percent. Furthermore, the introduced implicit method can potentially be used to study the mechanical properties of other materials with dopant impurities such as n-type and p-type semiconductors. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.