Papers by Author: Amit Misra

Abstract: Cu-Nb nanolayered material was produced through an accumulative roll bonding (ARB) technique. Using this technique, two different rolling schedules were employed to produce a normal and transverse rolled material. This resulted in specimens with differing microstructures within the 135nm thick nanolayers and interface structures between the layers. The dynamic response of these bulk Cu-Nb nanocomposites was then investigated under planar shock loading. It was observed in dynamically fractured specimens that the characteristics of ductile failure features formed on the fracture surface after dynamic loading were dependent upon the processing route of the nanocomposite. Specifically, grain shape differences due to dissimilar rolling passes are linked with differences in the failure response, particularly kinetics of fracture. In addition, incipient failure immediately below the primary fracture surface was also observed. Numerous nanovoids were nucleated and aligned linearly in the middle of Cu layers within the shocked Cu-Nb nanocomposites. These observations indicate relative stability of Cu-Nb interfaces produced by the ARB methods utilized in this study under dynamic loading conditions.

Abstract: Experimental studies proved that structures and properties of misfit dislocations and their intersections (nodes) in semi-coherent interfaces strongly affect thermal and mechanical stability of interface. Employing atomistic simulations, we reveal that misfit dislocation lines can exhibit a spiral pattern (SP) or remain straight in association with dislocation character at nodes. By analyzing nodes formation processes in terms of kinetics and energetics, we found that the variation is ascribed to the competition between core energy of misfit dislocation and interface stacking fault energy with respect to coherent interface.

Abstract: In recent years, the high strength of nanomaterials has gathered much interest in the materials community. Nanomaterials (polycrystalline and composites) have already been used, largely by the semiconductor community, as critical length scales for chip design have decreased to tens of nanometers. However, to ensure reliability of nanomaterials, the mechanisms underlying their structural integrity must be well understood. For these materials to be put into service, not only should their strength be considered, but also ductility, toughness, formability, and fatigue resistance. While some progress has been made into constructing models for the deformation mechanisms governing these behaviors, the body of experimental knowledge is still limited, especially for length scales below 10 nanometers. The results described here show stress-strain curves for nanolaminate composites with individual layer thickness of 40 nm and 5 nm. Nanolaminate composites fabricated via magnetron sputtering comprised of alternating 5 nm thick Cu and Nb multilayers (two relatively soft metals) exhibit strengths on par with hardened tool steel and deformability in compression in excess of 25% [1]. The deformability of nanoscale composites is found to be limited by the onset of geometric instability.

Abstract: A new technique of continuous severe plastic deformation (SPD)-processing, i.e. ECAP (equal channel angular pressing)-Conform is applied for the first time to produce long-length rods of commercial purity Ti with ultrafine-grained structure. The paper reports on the results of investigation of the microstructure and mechanical properties of Ti rods processed by ECAPConform and the following wire drawing.