Part I: Anisotropy of cracking from oxygen-induced dynamic embrittlement in bicrystals of IN718

It is shown that cracking from oxygen-induced dynamic embrittlement in bicrystals of the nickel-base superalloy IN718 having symmetrical Σ = 5 (013) tilt boundaries is considerably more rapid in the fast-diffusion direction parallel to the tilt axis than in the direction perpendicular to this axis. This lends support to the model that envisions the process as caused by diffusive penetration of grain boundaries ahead of a sharp crack by a surface-adsorbed embrittling element.