APPLICATION OF THE EMBEDDED ATOM METHOD TO FRACTURE, DISLOCATION DYNAMICS, AND HYDROGEN EMBRITTLEMENT.

A modern theory of metallic cohesion, the Embedded Atom Method, provides a simple and practical means of calculating atomistic processes related to the mechanical properties of metals. Energy minimization and molecular dynamics simulations in nickel, using the Embedded Atom Method, reveal how hydrogen at the crack tip can influence brittle fracture and dislocation dynamics. The authors find that hydrogen is bound to the crack tip, and hydrogen near the crack tip can affect the brittle fracture stress in two ways. First, hydrogen on the crack plane can weaken the metal bonds. Second, hydrogen in significant concentrations away from the crack plane modifies the moduli. The brittle fracture results can be interpreted in terms of the Griffith fracture criterion, leading to an interpretation based on the similar concepts of decohesion and surface energy reduction. The authors also conclude that hydrogen can strongly influence edge dislocation motion at low stresses. This effect is understood in terms of the binding of hydrogen to the dislocation core. At low stresses, the binding is sufficiently strong that a few hydrogen atoms can pin the dislocation. The Embedded Atom Method should be an effective tool in atomistic calculations and should replace the use of pair potentials.