High-angle Tilt Boundaries Research Articles

High-Angle Tilt Boundary—A Dislocation Core Model

The dislocation model of a symmetric tilt boundary is modified to take into consideration the stress field of the cores of the dislocations. It is found that such modification enables discussion of many properties of high-angle tilt boundaries including porosity, strain energy, intergranular fracture, grain boundary shearing, void formation, preferential melting, preferential diffusion, boundary migration, segregation, precipitation, amorphous behavior, continuous and discontinuous transition, etc., in terms of the interaction among the cores of the dislocations and the properties of the cores themselves. This is a first attempt to devise a working model capable of interpreting all the properties of grain boundaries. Unlike other models which are designed to have a few particular properties in a limited angular range, this model has the advantage of reducing to the dislocation model at low angles and of providing for amorphous behavior at high angles. The characteristic of a grain boundary of behaving as an ordered liquid of lower density is pointed out. The picture of a high-angle boundary is that it contains an equilibrium number of jogs which control many mechanical as well as thermochemical properties.

Grain Boundaries in Germanium

The relative energies and the boundary orientations of simple tilt boundaries in germanium crystals have been measured. The measurements were made on columnar tricrystals prepared by the modified Czochralski method. The orientations of the columnar tricrystals were either 〈100〉 and 〈111〉 isoxial or (100) isoplanar. The relative grain boundary energies were measured as a function of the angular misorientation θ between two grains. The crystallographic orientations of the grain boundary plane were also determined. It was found that the relative energy of 〈100〉 and 〈111〉 tilt boundaries up to about 15° of misorientation changes with misorientation as predicted by Read and Shockley's theory. For larger angles of misorientation, the grain boundary energy is essentially independent of the angle of misorientation. This indicates a significant but continuous change in boundary structure at the transition region. Additional evidence for the difference in the structure of low- and high-angle tilt boundaries was found in the apparent strong dependence of the energy of low-angle boundaries on the boundary orientation. Low-angle (100) twist boundaries were not observed.