Propagation of Slip across a Twist Boundary by Means of Grain-Boundary Twist-Disclination Loops

A new mechanism is proposed by which the motion of an edge dislocation across a twist boundary can be accomplished without recourse to dislocation climb. This mechanism involves the creation of a twist-disclination loop in the plane of the grain boundary and with an angle of rotation equal to the angle of misorientation. This will bring the two grains to crystallographic match within this loop and allows the edge dislocation to slip from one grain to the other through this disclination loop. An order-of-magnitude calculation for the diameter of the loop (≈ 70 Å at θ=5°) shows that these loops can be observed within the electron microscope.