The formation energy of triple lines

Abstract Triple lines occur where three grain boundaries intersect and are an intrinsic part of the defect structure of a material. Grain boundaries and dislocations both contribute a positive excess energy as they represent a deviation from the pristine lattice. By contrast, a triple line is formed within an already defective region of a material and so the formation energy need not be positive. A Gibbsian method is presented to find the formation energy of a triple line in a model for aluminium using molecular dynamics exploiting the symmetry of two related simulation cells. Approximately 83% of our 615 simulations produced a negative triple line formation energy with a moderately strong negative correlation with the mean excess grain boundary energy of the adjoining grain boundaries. The triple line formation energy was particularly sensitive to changes in its position and the associated spatial gradient provides an additional force acting on the triple line which is not included in the Herring relationship. Furthermore, this energy gradient would contribute to the driving force acting on a triple line and influence the drag effect of triple lines during grain growth.