Papers by Author: Michael Ferry

Abstract: Lamellar bands are the primary structural features in accumulative roll bonding (ARB) of sheet metals. The structural refinement in ARB sheets occur by forming a dense distribution of lamellar band boundaries. The lamellar band boundaries initiate as low angle interfaces, parallel to the existing lamellar band boundaries, irrespective of the crystallographic orientations of the parent lamellar bands. From an extensive investigation it was found that the transverse directions across the lamellar band boundaries are rotated by an angle equal to their misorientations. Such a phenomenon is not sustained when the boundaries turn to high angle.

Abstract: The crystallographic alignment of microbands in a Goss oriented single crystal was investigated by two and three dimensional electron back scatter diffraction. The microband boundaries were found to be curved instead of being perfectly flat interfaces, and the overall alignment closely matched a potential slip plane. The bumps and curved were created during subsequent deformation and, thus, deviates the microband boundaries from crystallographic nature.

Abstract: Sheets of commercial purity aluminum and super saturated solid solution of 0.3% Sc were accumulatively roll bonded to form 64 alternating layers in a 0.5 mm thickness. The rolling was done at 350 °C to ensure dynamic recovery/recrystallization in Al layers and precipitation hardening of Al(Sc) layers during the rolling. The sheet crystallographic texture was distributed along β fibre orientations. The recrystallization texture of aluminum layers after annealed at 250-350 °C was randomly distributed. The tensile property of this novel composite has achieved a small improvement over the commercially available grades and delamination between the layers was identified as the key issue to improve in this fabrication technique.

Abstract: 3-D FIB-EBSD tomography was used to analyze the structure and crystallography of nuclei, and nucleation process in 3-D space during annealing a cold rolled IF steel. It is revealed that the structure of nucleus at its very initial formation stage can be divided into two parts: (1) nucleation core, having a dislocation-contained subgrain structure, mainly bounded by low angle grain boundary with surrounding deformation subgrain, (2) newly-grown region, having a dislocation free structure, formed from high store energy deformation structures surrounding nucleus, and mainly bounded by high angle grain boundary.

Abstract: A novel methodology of predicting specific compositions for glass forming alloys based on elemental cluster selection, liquidus lines, atomic packing efficiency and ab initio calculations is presented and discussed. The proposed composition selection model has lead to the discovery of a number of novel, soon to be reported Mg, Cu, Zn and Ag-based bulk metallic glasses. The proposed model may also be used to explain high glass forming ability and physical properties of known BMG compositions and to pin-point new or superior BMG compositions in existing glass forming systems. Further, the aforementioned model shows strong correlations between proposed elemental clusters, glass forming ability and BMG ductility. This model has also shown applicable adaptation to known ceramic oxide glass forming systems.

Abstract: Accumulative Roll Bonding (ARB) is a severe plastic deformation technique for producing ultra-fine grain structures in sheet metal. In this investigation, the through-thickness shear strain distribution during single pass rolling of roll-bonded aluminium sheets was monitored via the deflection of an embedded scratch on the through-thickness, pre-polished surface of the material. It was found that, near the sheet surface and at its mid-thickness, rolling generated severe and moderate shearing, respectively. Such shearing was found to have a strong influence on the microstructure and crystallographic texture of the material, which was eliminated during subsequent rolling cycles. Compared to the core of a given rolled layer, both the microstructure and texture at the interface of the layers was inhomogeneous.

Abstract: A multilayered sheet composite of commercial purity Al and Al-0.3%Sc alloys was produced by accumulative roll bonding. The final sheet material consisted of 64 ultra fine grained layers, each of ~7.8mm in thickness. The as-deformed material was annealed at temperatures ranging from 250 to 350°C to study the changes in microstructure and their associated influence on mechanical properties. The as-deformed structures largely comprised of high angle grain boundaries in the Al layers and low angle grain boundaries in the Al(Sc) layers. During annealing, the structures in the Al(Sc) layers remained unaltered, whereas the Al layers recrystallized rapidly to the full layer thickness. The mechanical properties of the Al-Al(Sc) composite were measured and found to be unique in strength and ductility with annealing temperature having a significant influence on these properties.

Abstract: A supersaturated Al-0.3 wt.% Sc alloy was cold deformed by ECAP to an equivalent von Mises strain of 9.2 then pre-aged at 350 °C to generate a fine-grained alloy with an average grain size of 1 μm. The microstructure was highly resistant to grain coarsening at temperatures up to 500 °C with a detailed statistical analysis showing that the initial grain size distribution was very close to lognormal and, throughout annealing, remained lognormal and the normalized frequency distribution was time/temperature invariant despite a moderate broadening of the size distribution. This behaviour is largely similar to subgrain coarsening during recovery and grain growth after recrystallization. The homogeneous evolution of the microstructure during annealing, coupled with no appreciable change in texture, is also consistent with the advanced stages of continuous recrystallization.

Abstract: The effect of initial microstructure (acicular ferrite (AF), polygonal ferrite (PF) and strip cast (SC)) on the recrystallization behaviour of low carbon (LC) steel was investigated. Steel strip samples (0.05 wt.% C) of 2 mm in thickness were heat treated to produce an AF and PF microstructure from coarse austenite. The AF, PF and a similar chemistry SC sample manufactured from a twin roll caster were cold rolled to 50, 70 and 90% reduction, and annealed for various times in the temperature range 580-680 °C. The evolution of microstructure during recrystallization was studied by optical microscopy and electron backscatter diffraction (EBSD) in the SEM. The initial microstructure was found to have a substantial influence on the recrystallization behavior. PF recrystallized more rapidly than AF with SC showing extremely sluggish recrystallization behaviour. The recrystallizing grains in these initial microstructures have a lognormal distribution and the recrystallized number density (grains/mm2) decreased during annealing, with the initial microstructures affecting the degree of this decrease in number density.

Abstract: A typical dual-beam platform combines a focused ion beam (FIB) microscope with a field emission gun scanning electron microscope (FEGSEM). Using FIB-FEGSEM, it is possible to sequentially mill away > ~ 50 nm sections of a material by FIB and characterize, at high resolution, the crystallographic features of each new surface by electron backscatter diffraction (EBSD). The successive images can be combined to generate 3D crystallographic maps of the microstructure. A useful technique is described for FIB milling that allows the reliable reconstruction of 3D microstructures using EBSD. This serial sectioning technique was used to investigate the recrystallization behaviour of a particle-containing nickel alloy, which revealed a number of features of the recrystallizing grains that are not clearly evident in 2D EBSD micrographs such as clear evidence of particle stimulated nucleation (PSN) and twin formation and growth during PSN.