The relation between the structure and mechanical properties of A σ = 51 tilt boundary in germanium

A series of Germanium bicrystals containing a 16° [011] tilt boundary has been deformed in high-temperature creep and analyzed by both high-resolution lattice-fringe imaging and conventional transmission electron microscopy. Before deformation, the structure of the boundary consists of a linear array of Lomer dislocations. Subgrain boundaries are produced by the deformation and intersect the original grain boundary. Absorption of lattice dislocations causes the interfacial structure to change along the boundary from one subgrain to another. Deviations from the Σ = 51 coincidence structure are accommodated by secondary dislocations. The secondary dislocations have non-primitive DSC-Burgers vectors. Upon entering the grain boundary, the deformation-produced lattice dislocations decompose into secondary dislocations. Their motion in the interface is associated with grain boundary migration and grain boundary sliding. However, the latter process could not be identified macroscopically and, therefore, appears to make a much smaller contribution to the total strain than it does in metals. It is also directly shown that screw dislocations with Burgers vector in direction of the tilt axis can pass through the boundary.