Papers by Author: B.J. Duggan

Abstract: In this study, SEM and Köhlhoff etching were employed to follow the rolling texture and microstructure development in 93/7 brass that had been homogeneously cold rolled to different plastic strains. Correlated with FEM to rolling process, the effect of strain field on rolling texture and microstructure development in rolled 93/7 brass is conducted and reasonable conclusion is obtained.

Abstract: At the entrance temperature of 300°C, the effect of mill temperature on the texture and microstructure evolution was worked to 85/15 α-brass by two rollings with mill temperatures calibrated as 28°C for one rolling and 55°C for another, in which TEM was employed to reveal the microstructures, and ODF to represent the related textures. From the experiment evidence, a detailed discussion was made and led to a conclusion: in current rolling, with recovery, mill temperature influences the rolling texture and microstructure development through chilling and the working temperature induced deformation mechanisms change, the former one affecting B intensities, by contrast, the latter one leading to a texture transition.

Abstract: In this work the nucleation of the Cube recrystallised grains in AA6111 was investigated. The alloys were cold rolled to 85% and then annealed at different temperatures in an air circulation furnace. X-ray diffraction was used to obtain global textures and for specific area of interest, Electron-Back Scattered Pattern (EBSP) was used. In order to observe the microstructures after rolling and partially annealing, Scanning Electron Microscopy (SEM) was used. It was found that the recrystallisation textures are strongly related to the annealing temperature. The recrystallisation texture after low temperature annealing gives a strong retained rolling texture and at high temperature, a fairly random texture with weak Cube and rotated Cube components. The difference in the volume fraction of Cube with different alloys and annealing temperature are related to the deformation microstructures. Cube bands are observed to be deformation bands on the rolling plane. During annealing, precipitates are formed on the deformation band boundaries and Cube nuclei which are formed in the deformation Cube band are restricted to growth due to the precipitates.

Abstract: The idea that a single subgrain is sufficient to produce a single recrystallised grain is the simplest explanation for the recrystallisation process. Likewise, a single Goss oriented grain arising from the primary recrystallisation process is the simplest unit which can give rise to a secondary Goss oriented grain. More complicated cluster models, for example subgrain coalescence is also considered feasible for primary recrystallisation, clusters of Goss oriented grains might be another mechanism for forming Goss oriented secondary grains. This paper examines the cluster theory using material which is produced by the ARMCO process which requires two stages of rolling. In order to achieve this aim it is necessary to destroy the connectivity between individual Goss oriented grains by using thin foils derived from sheet which gives a strong Goss texture on conventional annealing. The foils were sectioned from the subsurface which had a strong η fibre after primary recrystallisation, and ranged in thickness from 18μm (the average grain size after primary recrystallisation) up to 80μm, which is the approximate thickness of the η textured layer. The central layer, which had the classical {111} primary recrystallised texture, was similarly processed, but this did not produce secondary recrystallisation. The experiment followed the secondary recrystallisation process in the same area using sequential annealing in a vacuum furnace by a combination of EBSD and Channelling contrast microscopy. The data does not support the high energy boundary hypothesis nor the CSL explanation. But it is clear that connectivity is important, because when this is destroyed by the thin foil two dimensional morphology, as it is in the thinnest foil, secondary recrystallisation does not occur.

Abstract: The relationship between the deformation orientation distribution function (ODF) and the primary recrystallised ODF in cold and warm rolled metals, is not a simple mathematical transformation from one to the other, but is through thermally activated processes occurring in the deformation microstructure. In BCC metals the mature rolling microstructure consists of cells, microbands and shear bands on a length scale of fraction of a micron, to deformation and transition bands at the grain scale, when this is of the order of 10 or more microns. There is evidence that grain boundary regions are sometimes distinct from grain interiors. Wherever there is a relatively sharp change in either orientation or microstructure such locations are potential sites of recrystallisation nuclei. In this paper the results of a systematic investigation of the development of microstructure in rolled interstitial free (IF) steel using both transmission and scanning electron microscopy are presented. It is shown how the dislocation mesh structure, formed at the earliest stages of rolling, develops into the mature microstructure consisting of cells, microbands and shear bands. Deformation heterogeneities in the microstructure, known to be of vital significance in the recrystallisation process are associated with the α and γ fibre components of the rolling texture. Shear band thickening and α grain fragmentation are also considered, since both processes can produce recrystallisation nuclei, which in the α fibre case can reduce desirable mechanical properties.

Abstract: 6111 Aluminium Alloy in the hot band state was cold rolled to 80% was then annealed at 450oC, 500oC and 540oC for recrystallization. The hot band was also solution heat treated, cold rolled and annealed to the same temperature to look at the difference in the recrystallization texture and precipitation states. It was found that the samples which were cold rolled and annealed without solution heat treatment gave Goss and P components after annealing. For the samples with solution heat treatment, the 450oC sample has a retained Cu type rolling texture while for the 500oC and 540oC the textures are quite random. The retained rolling texture found in the 450oC sample is due to the fact that it was partially recrystallized as the precipitates prevent complete recrystallization. The difference in the precipitation states during and after annealing of the samples with and without solution heat treatment affects the final recrystallization texture.

Abstract: SiCp/Zn-22 wt% Al metal matrix composites of different particulate sizes have been prepared and tensile tested at 250°C at various strain rates. Scheduled thermomechanical treatment of structural refinement was employed to enhance the ductility of the composites. Substantial ductility of over 500% elongation bas been achieved within the strain rates investigated. The highest elongations are generally obtained by the samples reinforced with large particulates. Microstructural examination of the tested samples shows significant material cavitation and particulate separation in the material after tensile deformation. It was found that the particles had a de-strengthening effect.