DYNAMIC SIMULATION OF DISLOCATION-MOTION IN L12 ALLOYS

A dynamical simulation for the motion of an isolated superdislocation (SD) under an applied stress has been developed. The simulation incorporates the concept that cross slip from {111} planes to {010} planes can locally pin the SD. This mechanism is believed to be responsible for the remarkable increase in the yield strength with increasing temperature exhibited by several intermetallic compounds with the L1(2) crystal structure (e.g. Ni,Al). Individual pinning events occur randomly with the probability of pinning depending on the local line orientation. The resulting spatial distribution of pinning points is non-random consisting of highly pinned segments oriented near screw character linked by unpinned segments of mixed character (superkinks), similar to the configurations typically observed in post-deformation substructures. The motion of the screw portions of the SD proceeds by the lateral motion of these superkinks. The glide velocity of the SD is found to be a significant fraction of the free-flight velocity. However, fluctuations in the population of superkinks along a given SD can lead to exhaustion of motion. It is concluded that the principal effect of cross-slip-pinning is not the reduction in the SD velocity, but rather the exhaustion of the density of mobile SDs. The implications of these results with respect to the modeling of both monotonic and transient deformation in these alloys are discussed.