Investigation of the influence of excess free volume on the mobility of triple junctions of grain boundaries

The effect of excess free volume on the mobility of triple junctions of grain boundaries by the example of nickel was studied by the molecular dynamics method. According to experimental data, triple junctions in polycrystals in most cases contain more specific free volume compared with the grain boundaries that form these junctions. Triple junctions of tilt boundaries with < 100 > and < 111 > misorientation axes were considered. Migration of the junctions was simulated by creating a nonequilibrium configuration of the joining boundaries - their migration, as a result of which they took an equilibrium position, led to migration of the triple junction (model proposed by L.S. Shvindlerman and co-authors). The interactions of nickel atoms with each other in the molecular dynamics model were described by the many-body Cleric-Rosato potential constructed within the tight binding model. The free volume was introduced locally into the triple junction region with the radius of 1 nm. The percentage of the removed atoms from the considered region was varied from 0 % to 80 %. Molecular dynamic simulation showed that the migration velocity of the triple junction is practically independent of the free volume value. This is explained by the fact that most part of the free volume introduced at the initial stage does not migrate with the triple junction but remains at the point where it was introduced and distributed along the boundary which lengthens during the migration of the junction. The smaller part of the free volume however remains in the joint but its presence has little effect on the mobility of the triple junction. This is mainly influenced by the mobility of the joining boundaries and the ratio of their tension.