Chemical Complexity in Mechanical Deformation of Metals

Abstract

Prediction of the deformation behavior of metals in the presence of environmentally embrittling species like water or hydrogen, or under presence of organic reactive chemicals, remains a critical challenge in materials modeling. Here we propose a combination of the first principles-based reactive force field ReaxFF and the embedded atom method (EAM) in a generic multi-scale modeling framework, the Computational Materials Design Facility (CMDF), that enables the treatment of large reactive metallic systems within a classical molecular dynamics framework. Our hybrid method is based on coupling multiple Hamiltonians by weighting functions, which allows accurate modeling of chemically active sites with the reactive force field, while other parts of the system are described with the computationally less expensive EAM potential. We apply our hybrid modeling scheme in a study of fracture of a nickel single crystal under the presence of oxygen molecules. We observe that the oxide formed on the crack surface produces numerous defects surrounding the crack, including dislocations, grain boundaries, and point defects. We show that the mode of crack propagation changes from brittle crack opening at the crack tip to void formation ahead of the crack and void coalescence for lll orientation of the crack. Our results illustrate the significance of considering oxidative processes in studying deformation of metals, an aspect largely neglected in most modeling work carried out with pure EAM potentials. Our hybrid method constitutes an alternative to existing methods that are based on coupling quantum mechanical methods, such as density functional theory, to empirical potentials.