The Scattering of Phonons by Infinitely Long Quantum Dislocations Segments and the Generation of Thermal Transport Anisotropy in a Solid Threaded by Many Parallel Dislocations

A canonical quantization procedure is applied to the interaction of elastic waves—phonons—with infinitely long dislocations that can oscillate about an equilibrium, straight line, configuration. The interaction is implemented through the well-known Peach–Koehler force. For small dislocation excursions away from the equilibrium position, the quantum theory can be solved to all orders in the coupling constant. We study in detail the quantum excitations of the dislocation line and its interactions with phonons. The consequences for the drag on a dislocation caused by the phonon wind are pointed out. We compute the cross-section for phonons incident on the dislocation lines for an arbitrary angle of incidence. The consequences for thermal transport are explored, and we compare our results, involving a dynamic dislocation, with those of Klemens and Carruthers, involving a static dislocation. In our case, the relaxation time is inversely proportional to frequency, rather than directly proportional to frequency. As a consequence, the thermal transport anisotropy generated on a material by the presence of a highly-oriented array of dislocations is considerably more sensitive to the frequency of each propagating mode, and, therefore, to the temperature of the material.

Dynamic Dislocation-Defect Analysis and SAXS Study of Nanovoid Formation in Aluminum Alloys

Crystalline defects other than the essential dislocations are produced by dislocation intersections resulting in debris, which can transform into loops, point defects, and∕or nanovoids. The stress concentrations ahead of slip clusters promote void formation leading to incipient cracks. To evaluate the progression of these processes during deformation, dynamic dislocation-defect analysis was applied to nominally pure aluminum, Al–Mg, and Al–Cu alloys. In the case of nanovoid formation, small angle X-ray scattering (SAXS) was used to quantitatively assess if the void size and its volume fraction can be determined to directly correlate with the measured thermodynamic response values. The SAXS signal from the nanovoids in nominally pure aluminum is distinctly measurable. On the other hand, thermomechanical processing of even nominally pure aluminum results in the formation of nanoprecipitates, which requires future calibration.

Dynamic Evaluation of Strength-Structure Properties by the Determination of Activation Volume and Mean Slip Distance

Measurements of the activation volume and mean slip distance were used in the dynamic dislocation-defect analysis to reveal the dislocation-obstacle evolution with strain. Due to the large effect of point defect mobility above 250 K on the strain rate sensitivity, fine-grained Al specimens with the grain-boundaries sealed and unsealed as vacancy sinks were tested at 300 K as the reference behaviour. The activation distance diagrams revealed that the artificially aged products in AA6111 and naturally aged extruded AA6063 can be used to examine the effect of chopping-up of particles on the ductility of the samples. Thus a means to examine strength-structure-ductility of specific products have been devised.