Atomistic modeling of the fracture of polycrystalline diamond

A series of molecular-dynamics simulations using a many-body interatomic potential has been performed to investigate the behavior under load of several 〈001〉 and 〈011〉 symmetrical tilt grain boundaries (GB’s) in diamond. Cohesive energies, the work for fracture, maximum stresses and strains, and toughness as a function of GB type are evaluated. Results indicate that special short-period GB’s possess higher strengths and greater resistance to crack propagation than GB’s in nearby misorientation angles. Based on dynamic simulations, it was found that the mechanism of interface failure for GB’s without preexisting flaws is not that implied by Orovan’s criterion, but rather GB strength is defined by GB type instead of cleavage energy. In simulations of crack propagation within GB’s on the other hand, it was found that critical stresses for crack propagation from atomistic simulation and from the Griffith criterion are consistent, indicating that GB cleavage energy is an important characteristic of GB toughness. Crack propagation in polycrystalline diamond samples under an applied load was also simulated and found to be predominantly transgranular rather than intergranular.