The stability of triple junctions
Abstract
The aim of this project is to study the stability of triple junction structures with respect to the 11 geometric degrees of freedom that are used to characterize them. There are three distinct stages of this project. The first stage involved designing a theoretically stable triple junction using Herring’s relation. The second step was to fabricate these stable triple junctions by growing three oriented columnar grains of copper in a Bridgman furnace. Third stage aim was to model grain boundaries and triple junctions as arrays of dislocations, and study the interactions of these dislocations and also calculate the energy associated with these arrays to find their relation with stability of the triple junctions. Various triple junction systems were identified for grains oriented with common lowindex directions, such as <100>, <110> and <111>. One of the systems found to be stable has misorientations as Σ5, Σ5, and Σ25 with a junction lying in the common [100] direction. Three tricrystals were grown with misorientation close to this geometry. Different deviations in misorientations were measured for the three tricrystals which resulted in varying stability of three tricrystals. The stability or instability of these tricrystals has been explained in terms of the deviations from observed misorientations. A computational dislocation model for the triple junction was constructed which successfully describes the forces acting on dislocations along the grain boundaries. It is shown that dihedral angles found using Herring’s relation and that obtained by this model are different. The dislocation model was also used to estimate energy associated with triple junctions and it is shown that the TJs have long-range strain fields somewhat like those of disclinations.
Degree
Ph.D.
Advisors
King, Purdue University.
Subject Area
Metallurgy|Materials science
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