Interfacial-dislocation-controlled deformation and fracture in nanolayered composites: Toward higher ductility of drawn pearlite

The excellent combination of high strength and high ductility of drawn pearlitic steels is likely derived from the synergistic effects between the ferrite and cementite phases. However, the detailed mechanism, especially the mechanism responsible for the improvement in ductility, has not yet been fully elucidated. In this study, to achieve improved ductility of drawn pearlitic steels, interfacial-dislocation-controlled deformation and fracture in nanolayered composites of ferrite and cementite phases with the Bagaryatsky relationship are investigated via uniaxial tensile and compressive deformation tests using molecular dynamics simulations. Various modes of inelastic deformation are observed at the yield point according to the spacing of interfacial dislocations on the interface between the ferrite and cementite phases in the nanolayered-composite models. Spacing of the interfacial dislocations, which accommodates misfit strains between the ferrite and cementite phases, determines the phase stress and the interfacial dislocation structure in the nanolayered-composite models. This phase stress and interfacial dislocation structure influences the resolved shear/normal stress and the critical resolved shear/normal stress for each inelastic-deformation mode, respectively. Thus, interfacial dislocation spacings can control which inelastic deformation mode is activated at the yield point. We find specific interfacial dislocation structures on the ferrite–cementite interface that nucleate lattice dislocations with lower Schmid factors at the first plastic event. This interfacial dislocation structure can improve the ductility of drawn pearlitic steels because the high strain-hardening rate in the ferrite phases, resulting from the nucleation of dislocations with lower Schmid factors, is clearly expected to suppress the concentration of plastic deformation in the cementite phase [T. Ohashi et al., Mater. Sci. Eng. A 588 (2013) 214–220]. The possibility of the interfacial-dislocation-controlled deformation and fracture enabling higher ductility of drawn pearlitic steels is discussed.