Papers by Author: John F. Humphreys

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Authors: Michael Ferry, Wan Qiang Xu, M. Zakaria Quadir, Nasima Afrin Zinnia, Kevin J. Laws, Nora Mateescu, Lalu Robin, Lori Bassman, Julie M. Cairney, John F. Humphreys, Adeline Albou, Julian H. Driver
Abstract: A focused ion beam (FIB) coupled with high resolution electron backscatter diffraction (EBSD) has emerged as a useful tool for generating crystallographic information in reasonably large volumes of microstructure. In principle, data generation is reasonably straightforward whereby the FIB is used as a high precision serial sectioning device for generating consecutive milled surfaces suitable for mapping by EBSD. The successive EBSD maps generated by serial sectioning are combined using various post-processing methods to generate crystallographic volumes of the microstructure. This paper provides an overview of the use of 3D-EBSD in the study of various phenomena associated with thermomechanical processing of both crystalline and semi-crystalline alloys and includes investigations on the crystallographic nature of microbands, void formation at particles, phase redistribution during plastic forming, and nucleation of recrystallization within various regions of the deformation microstructure.
Authors: Ali Gholinia, Ian Brough, John F. Humphreys, Pete S. Bate
Abstract: A combination of electron backscatter diffraction (EBSD) and focused ion beam (FIB) techniques were used to obtain 3D EBSD data in an investigation of dynamic recrystallization in a Cu-2%Sn bronze alloy. The results of this investigation show the origin of the nucleation sites for dynamic recrystallization and also elucidates the orientation relationship of the recrystallized grains to the deformed, prior grains and between the dynamically recrystallized grains.
Authors: John F. Humphreys
Authors: Michael Ferry, John F. Humphreys
Abstract: Copper single crystals of {110}<001> crystallographic orientation were cold rolled to a true strain of 1.4. Specimens were cut from the as-deformed crystals with all surfaces mechanically ground and deep-etched in concentrated nitric acid to minimise the likelihood of surface nucleation of recrystallized grains during subsequent annealing. The early stages of static recovery were studied by annealing specimens at 300 oC. The crystallographic features of the deformed and annealed microstructures were determined by high resolution electron backscatter diffraction. It was observed that deformation was homogeneous with the microstructure in ND-RD plane exhibiting two complementary sets of intersecting bands at ~+ 35o to ND. Along these bands and in the microstructure, in general, there was an overall spread in orientation about ND towards {110}<112>. However, the orientation spread along these bands was cyclic, that is, sinusoidal orientation gradients were generated about ND with amplitude of up to 20o and wavelength 5-10 µm. Annealing resulted in the preferred growth of cells that have orientations at the edge of the orientation spread of the deformation substructure. This localized coarsening of the microstructure is similar to the discontinuous subgrain growth observed in {110}<001> oriented Al single crystals and indicates that discontinuous subgrain (cellular) growth can also occur in metals of lower stacking fault energy.
Authors: J. Dennis, Pete S. Bate, John F. Humphreys
Abstract: Grain growth may occur in two forms, normal grain growth, characterized by a constant grain size distribution during growth, and abnormal grain growth, where one or more abnormally large grains may form in the microstructure. The presence of abnormally large grains in an otherwise uniform microstructure may be detrimental to the mechanical properties of a polycrystalline structure. Little is understood of the exact cause of abnormal grain growth. The annealing conditions leading to the onset of abnormal grain growth have been investigated via a series of grain growth experiments carried out on an Al-4wt%Cu alloy. The structure of which consisted of equiaxed grains (<8μ) pinned by a fine dispersion of sub-micron second phase particles, which may dissolve upon annealing. Minority texture components may experience accelerated growth due to a higher energy and mobility compared to the surrounding grain structure. The combination of these two events may result in the abnormal growth of some grains. SEM imaging and EBSD data has then made it possible to characterize the influence of particle dissolution and grain boundary misorientation on the onset of abnormal grain growth. The stability of ‘island grains’ found to exist internally in abnormally large grains has also been investigated in relation to the misorientation relationship and localized second phase volume fraction found there. There was only weak evidence of special misorientation relationships between the island grains and the abnormally large grains in which they exist, and although there was evidence of an enhanced fraction of pinning particles at island grain boundaries, this was also true of boundaries in general. The larger size of island grains is their dominant characteristic, and grains which become island grains may have been incipient abnormal grains.
Authors: Wan Qiang Xu, Michael Ferry, Julie M. Cairney, John F. Humphreys
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.
Authors: John F. Humphreys, Michael Ferry
Authors: A.W. Bowen, M.G. Ardakani, John F. Humphreys
Authors: Pete S. Bate, K.B. Hyde, S.A. Court, John F. Humphreys
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