Dynamic behavior of grain boundaries with misorientations in the vicinity of S3 coherent and incoherent twin boundaries in Al bicrystals

The migration behaviour of different grain boundaries with misorientations close to the & sigma;3 CSL orientation relationship in high purity Al bicrystals under the capillary driving force and applied mechanical stress was investigated. The experiments were performed by an in-situ technique to observe and measure the boundary migration with a scanning electron microscope. The ability of the nearly & sigma;3 60 degrees 111 incoherent {110} and {112} boundaries to move under capillary driving force was found to depend critically on the initial boundary inclination. While boundaries with inclinations near {112} can easily assume a curved shape and migrate, boundaries with an initial {110} plane remain stationary or form non-mobile facets. This is attributed to the essential anisotropy of the inclination dependence of the energy & gamma;(& psi;) of 60 degrees 111 tilt boundaries with differently high torque d & gamma;/d & psi; around {112} and {110} inclinations, as revealed by atomistic simulations of the respective boundaries. The & sigma;3 70.5 degrees 110 tilt boundary with the geometry corresponding to the coherent {111} twin boundary, was found to be immobile under both driving forces applied. The 59.2 degrees 111 tilt grain boundary with geometry near the & sigma;3 {110} incoherent twin boundary was found to be quite mobile under applied shear stress. The measured migration activation enthalpy H = 0.45 eV for this boundary is the lowest among the values obtained in previous experiments for any other stress driven grain boundary in Al bicrystals of the same purity. Moreover, this boundary migrated with a zero coupling factor, i.e. without producing any measurable shear parallel to the boundary plane.

Automated summary

The migration behavior of grain boundaries with misorientations close to the & sigma;3 CSL orientation relationship in high purity Al bicrystals was investigated. It was found that the ability of some boundaries to move under capillary driving force depends on the initial boundary inclination. The measured migration activation enthalpy for one specific boundary was found to be the lowest among previous experiments in Al bicrystals of the same purity.