Biomedical subjects

F J Humphreys

Publications and source records attributed to F J Humphreys.

4 recordsLinked to original sources

PubMed2002

Characterizing the deformed state in Al-0.1 Mg alloy using high-resolution electron backscattered diffraction.

The application of high resolution electron backscatter diffraction (EBSD) in a field emission gun scanning electron microscope to the characterization of a deformed aluminium alloy is discussed and the results are compared with those obtained by transmission electron microscopy. It is shown that the adequate spatial resolution, accompanied by the improvement in angular resolution to approximately 0.5 degrees that can be achieved by data processing, together with the extensive quantitative data obtainable, make EBSD a suitable method for characterizing the cell or subgrain structures in deformed aluminium. The various methods of analysing EBSD data to obtain subgrain sizes are discussed and it is concluded that absolute subgrain reconstruction is the most accurate.

Journal Article↗

PubMed2002

The application of a hot deformation SEM stage, backscattered electron imaging and EBSD to the study of thermomechanical processing.

The technique of combining in situ hot-deformation and high resolution electron backscattered diffraction (EBSD) has been applied to study the mechanisms operating during the thermomechanical processing of metals. A simple hot tensile-straining stage is installed in a field emission gun scanning electron microscope equipped with an EBSD system and has been used successfully for a number of preliminary investigations. These investigations include substructure formation, dynamic subgrain and grain growth, superplastic deformation in aluminium alloys, and dynamic recrystallization in copper. Despite the surface topography, which inevitably increases during plastic deformation, channelling contrast backscattered electron micrographs have been successfully obtained after strains of up to approximately 50%. Good quality EBSD maps have been obtained after strains of up to 100%. Most observations and measurements from the in situ experiments are consistent with what is known about the mechanisms occurring in the bulk. The microstructures revealed in the centre of the in situ samples after later repolishing are generally similar to those at the surface.

Journal Article↗

PubMed2001

Orientation averaging of electron backscattered diffraction data.

The use of data averaging to improve the angular precision of electron backscattered diffraction (EBSD) maps is discussed. It is shown that orientations may be conveniently and rapidly averaged using the four Euler-symmetric parameters which are coefficients of a quaternion representation. The processing of EBSD data requires the use of an edge preserving filter and a modified Kuwahara filter has been successfully implemented and tested. Three passes of such a filter have been shown to reduce orientation noise by a factor of approximately 10. Application of the method to deformed and recovered aluminium alloys has shown that such data processing enables small subgrain misorientation (< 0.5 degrees ) to be detected reliably.

Journal Article↗

PubMed1999

High resolution electron backscatter diffraction with a field emission gun scanning electron microscope.

A scanning electron microscope with a thermal field emission gun (FEGSEM) is found to offer significant improvements in electron backscatter diffraction performance over a conventional W-filament scanning microscope. The spatial resolution is improved by a factor of approximately 3 in the FEGSEM and is optimized at probe currents of 50-300 nA and at 10-15 keV. The angular accuracy is optimized at probe currents above approximately 150 nA and at 30 keV.

Microscopy, Electron, Scanning↗