The possibility of the rotation of a subgrain with respect to its neighbors as a natural process during recrystallization is analyzed thermodynamically and kinetically. It is found that it is energetically possible if the direction of rotation favors the elimination of low‐angle boundaries over that of high‐angle boundaries, the elimination of twist and asymmetric boundaries over that of the tilt and symmetric boundaries, and the elimination of the large‐area boundaries over that of the small‐area boundaries. Since the rotation direction has two degrees of freedom, there exists a relation between the two degrees of freedom such that directions whose two degrees of freedom fulfill such a relation provide no driving force for rotation. All other directions will supply free energy to rotate in one sense or the opposite. Kinetically one of the following two processes within one boundary can be rate‐controlling: the cooperative movement of dislocations in the boundary, and the cooperative diffusion of vacancies in the lattice. The rotation of a subgrain favors the elimination of one of the boundaries which contributes the largest fraction of driving force and also the largest fraction of resistance. This causes the subgrain to coalesce with the other subgrain separated by this boundary. The estimated time required for one such coalescence compares favorably with the observed rate of subgrain growth in Al.

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In the case of whisker dekinking, the dislocations will disappear at the free surfaces. In the case of subgrain rotation, since the structure of subboundaries is determined by the relative orientation of the subgrains, if the subgrains are rotating rigidly, there will be a natural annihilation process or dislocation reactions at the subboundary junctions.
19.
This arises from the consideration that jogs on the edge dislocation move along the dislocation with a mobility the same as that of atoms, namely, D/kT. The dislocation climbs a distance b when each jog travels the average distance between two jogs on the dislocation, namely, 2b for the largest possible jog density. Let the driving force be F per unit length for the climb of the whole dislocation. The driving free energy supplied per unit length of dislocation when the dislocation climbs a distance b is Fb. This driving energy, when distributed uniformly to the jogs, supplies 2Fb2 per jog. Since each jog travels 2b in the same time interval, the average driving force on the jog is Fb which can be shown to be independent of the jog density. With this driving force the jogs move with a velocity of FDb/kT. This indicates that the whole dislocation will climb with the velocity of FDb/2kT or it has the mobility of Db/2kT. The above argument can be applied to the case where the jog density is j per unit length which is less than 1/2b. Then the mobility for the climb of the edge dislocation is given by Eq. (19).
20.
This means that the rate of production of vacancies, or the dislocation climb process, is faster than the rate of diffusion of vacancies from one half of the wall to the other half.
21.
The motion of the screw dislocation is controlled by the mobility of the jogs. Unlike the case of an edge dislocation where the jogs climb along the dislocation line, the jogs on a screw dislocation climb perpendicularly to the dislocation line. The driving force acting on the jog is independent of the jog density in the case of the edge dislocation but is inversely proportional to the jog density in the case of the screw dislocation.
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See reference 11, p. 185.
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See reference 11, p. 186.
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© 1962 The American Institute of Physics.
1962
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