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G M Pennock

Publications and source records attributed to G M Pennock.

3 recordsLinked to original sources

Electron backscattered diffraction as a tool to quantify subgrains in deformed calcite.

In this work, we investigated processing methods to obtain subgrain sizes from electron backscattered diffraction data using samples of experimentally deformed calcite (CaCO(3)) polycrystals. The domain boundary hierarchy method, based on area measurements of domains enclosed by boundaries larger than a given misorientation angle, was applied to these calcite samples and was found to be limited by: (i) topological problems; (ii) undersampling of large grains; and (iii) artefacts caused by nonindexing. We tested two alternative methods that may reduce the problems: (i) the measured linear intercept hierarchy method, based on measurements of linear intercept between boundaries having larger misorientations than a given minimum angle; and (ii) the calculated linear intercept hierarchy method, based on the total length of boundaries having misorientations larger than a given minimum angle. The measured linear intercept hierarchy method was found to produce results more representative for the microstructure than the calculated linear intercept hierarchy method, because the calculated linear intercept hierarchy method has a significant uncertainty related to the grid-based nature of the measurements. Preliminary results on calcite suggest that the measured linear intercept hierarchy method is related, in a complex way, to deformation conditions such as stress, strain and temperature as well as to the characteristics of subgrain rotation and grain boundary migration processes.

Journal Article↗

Low-angle subgrain misorientations in deformed NaCl.

The development of subgrain boundary misorientations with strain in NaCl polycrystals has been investigated. At low strains, a power law relationship exists between strain and average misorientations. The accuracy of this relationship is assessed in terms of material and electron backscattered diffraction (EBSD) processing parameters and is found to hold for a material of constant grain size deformed in compression, providing EBSD mapping and processing conditions were similar. Average misorientations are strongly influenced by grain orientation, suggesting that the misorientation-strain relationship may also be texture dependent in materials with high plastic anisotropy. A slight grain size dependency of the average misorientations was observed.

Crystallization↗

Misorientation distributions in hot deformed NaCl using electron backscattered diffraction.

EBSD orientation mapping has been used to derive subgrain boundary misorientation distributions in a series of hot deformed and etched NaCl samples. The main objective of this study has been to examine the influence of data processing, noise caused by angular resolution limits and step size on the subgrain misorientation distributions in hot deformed NaCl. Processing of non-indexed EBSD patterns increased the average misorientations in etched NaCl. Noise contributed significantly to low angle misorientation peaks for step sizes less than the minimum subgrain size. Orientation data collected using a step size larger than the average subgrain size cumulated misorientations across individual subgrains and effectively measured an orientation gradient between steps. Orientation gradient distributions were not influenced by noise. Average misorientation values calculated from large step data correlated well with average misorientation from small step size data, Average misorientations showed a power law relationship with strain. Three types of substructures were identified using scanning electron microscopy and EBSD mapping, equiaxed subgrains, long subgrain boundaries and a core-mantle subgrain arrangement.

Journal Article↗