Atomistic modeling of the fracture of polycrystalline diamond

A series of molecular-dynamics simulations using a many-body interatomic po tential has been performed to investigate the behavior under load of severa l [001] and [011] symmetrical tilt grain boundaries (GB's) in diamond. Cohe sive energies, the work for fracture, maximum stresses and strains, and tou ghness as a function of GB type are evaluated. Results indicate that specia l short-period GB's possess higher strengths and greater resistance to crac k propagation than GB's in nearby misorientation angles. Based on dynamic s imulations, it was found that the mechanism of interface failure for GB's w ithout preexisting flaws is not that implied by Orovan's criterion, but rat her GB strength is defined by GB type instead of cleavage energy. In simula tions 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 polycr ystalline diamond samples under an applied load was also simulated and foun d to be predominantly transgranular rather than intergranular.