Superlattice Dislocations Research Articles

Theoretical Analysis of Plastic Deformation in Superlattices Based on the Body-Centered Cubic Structure

A theoretical analysis has been made of the friction stress opposing the movement of both superlattice slip dislocations and twinning dislocations which arises from their interaction with antiphase domains in B2-, DO3-, and L21-type superlattices, all of which are based on the body-centered cubic structure. In the case of superlattice slip dislocations, this interaction results in the well-known maximum in yield stress at some critical antiphase domain size. Twinning dislocations, on the other hand, require stress levels about twenty times greater than the maximum value calculated for superlattice dislocations; however, this friction stress decreases for domains smaller than the critical size. In both DO2- and L21-type superlattices, second nearest neighbor as well as first nearest-neighbor ordering energies are found to play an important role in the resistance to dislocation motion. These results agree well with the limited number of experimental observations obtained by other investigators with the Fe3Al superlattices.

Dislocation Substructure vs Transgranular Stress Corrosion Susceptibility Of Single Phase Alloys

Abstract The microstructure of deformed alloys which are susceptible to stress corrosion cracking has been investigated by transmission electron microscopy. It is found that the mode of failure is strongly related to the dislocation distribution. Alloys with a cellular arrangement of dislocation tangles have superior resistance to transgranular failure, whereas alloys containing planar groups of dislocations are generally more susceptible. In alloys, the active path for preferential electrochemical attack during transgranular stress corrosion cracking is associated with a continuous plane of disordered material which is created by the motion of dislocations through a matrix of short-range order. In superlattices, it is proposed that the active site for chemical attack is the antiphase boundary created during deformation by the accidental separation of superlattice dislocation pairs. The susceptibility of annealed, fully ordered single crystals to chemical embrittlement is predicted to depend on the contin...

Theory and direct observation of dislocations in the Fe 3Al superlattices

It has been found that in order for dislocations to travel through superlattices of the type D0 3, L2 1 and B2 without creating any net disorder across the slip plane, they must move as superlattice dislocations. A theoretical analysis of the superlattice dislocations in the D0 3 and L2 1 type structures shows that they should consist of four 1 2 a 0 〈111〉 type ordinary dislocations bound together by two different type antiphase boundaries. On the other hand, superlattice dislocations in the B2 structure consist of pairs of coupled dislocations. Calculations have been made of the separation between the superlattice dislocations for the specific case of the Fe 3Al alloy exhibiting both D0 3 and B2 type ordered lattices. It has been found that for this specific alloy, the antiphase boundary energy associated with the superlattice dislocations is relatively low, resulting in a large extension of the individual dislocations constituting the superlattice dislocation. Because of this low energy, the possibility is suggested that dislocations might move through the Fe 3Al lattice as ordinary 1 2 a 0 〈111〉 types. In order to determine experimentally whether or not dislocations travel through the lattice as superlattice dislocations or as ordinary dislocations, for the particular Fe 3Al alloy possessing both D0 3 and B2 type structures, thin foils of the alloy were examined using transmission electron microscopy. It was indeed found that the dislocations in this alloy travel as ordinary dislocations, leaving behind on their slip plane ribbons of antiphase boundaries. In addition, a preponderance of screw dislocations were observed to be present, which in turn gives rise to wavy or noncrystallographic type slip behavior.

Dislocation configurations in AuCu 3 and AuCu type superlattices

Superlattice dislocations have been observed for the first time by transmission electron microscopy techniques carried out with thin films of AuCu 3. These consist of two pairs of partial dislocations held together by an antiphase domain boundary. The separation between the pairs is measured to be about 130 Å. A theoretical calculation has also been made of the expected spacing which involves the stacking fault energy, antiphase domain boundary energy and the elastic interaction energies between the individual dislocations that constitute the superlattice dislocation. The theoretical results are in good agreement with those observed experimentally. Further theoretical considerations of the AuCu type structure lead to two additional dislocation configurations characterized by the direction of their Burgers vectors with respect to the ordered lattice. This difference in the dislocation configurations between AuCu 3 and AuCu arises because the latter is a less symmetrical lattice.