Answer to Question #350404 in General Chemistry for justin

Question

Briefly explain why small-angle grain boundaries are not as effective in interfering with the slip process as are high-angle grain boundaries.

Answer 1

Small-angle grain boundaries are not as effective in interfering with the slip process as are high-angle grain boundaries because there is not as much crystallographic misalignment in the grain boundary region for small-angle, and therefore not as much change in slip direction.

According to common belief high angle grain boundary region because of their disordered almost liquid like structure that acts as a strong barrier against dislocation slip motion and causes actually formation of dislocations file-up against it by arresting their motion unless that the stress concentration at the leading dislocation becomes high enough to go though the barrier. Low angle grain boundaries (quasi-coherent) on the other hand are formed by the dislocation network aligned along the geometric plane with small tilt angle differences between successive counterparts (i.e., tilt boundary made up edge dislocations) therefore it may only divert the slip direction of the incoming gliding dislocation with very small frictional stresses.