Representation of grain misorientations (mesotexture) in Rodrigues-Frank space

Use of the Rodrigues vector R for representation of rotations in Rodrigues-Frank (RF) space is illustrated for the particular case of misorientations between grains in a cubic polycrystal. A subvolume of the fundamental zone of RF space is shown to be a convenient unit for the display of preferred misorientation, which here is referred to as ‘mesotexture’. When a misorientation sample population is displayed in the subvolume low angle, coincident axial direction and particularly coincident site lattice boundaries are presented with clarity thus allowing nature of the mesotexture to be assessed. Some features and properties of RF space are illustrated with reference to an experimental sample population of grain misorientations, and comparisons are made with other representation methods.

Grain boundary character distributions in Ni-16Cr-9Fe using selected area channeling patterns: methodology and results

Selected area channeling patterns imaged on an SEM are digitized and displayed on the screen of a Macintosh computer, on which the user selects channeling bands that are measured to determine orientation. Grain boundary misorientations are found using the orientation information for pairs of grains adjacent at grain boundaries, and the boundaries are classified as low angle boundaries (LABs), coincident site lattice boundaries (CSLBs), or general boundaries (GHABs) based on the misorientation information. The technique was implemented to analyze the grain boundary character distributions (GBCDs) in Ni-16Cr-9Fe. The GBCDs of solution annealed material were similar to those expected in an aggregate of randomly oriented polycrystals. However, sequential thermomechanical treatments (5% tensile strain + 945 degrees C:75 min + 2% tensile strain + 890 degrees C:15 h + 3% tensile strain + 890 degrees C:20 h or 9% compressive strain + 890 degrees C:20 h + 9% compressive strain + 890 degrees C:20 h + 3% compressive strain + 890 degrees C:15 h) applied after the solution anneal lowered the proportions of GHABs in the GBCDs from 76-79% to 47-64%. The CSL-enhanced GBCDs of both the tensile-deformed samples and the compression-deformed sample appear to have evolved mainly through impingement of twin and twin-related boundaries during recrystallization; the CSL-enhanced GBCD of a compression-deformed sample appears to have been influenced by grain rotation processes to a greater degree than were the tensile-deformed samples The CSL boundaries in the CSL-enhanced GBCDs were, in general, closer to the exact CSL misorientations than were those in the near-random GBCDs of the solution annealed material. An analysis of the distribution of misorientation axes did not indicate any correlation between grain misorientation texture and GBCD evolution.

Measurement of lattice parameter and strain using convergent beam electron diffraction

A brief review is presented of the methods of measuring lattice parameters and strain using diffraction techniques. The presence of strain leads to broadening of diffraction maxima, which is normally separable from any broadening caused by size. The special advantages of the convergent beam electron diffraction (CBED) technique is the local nature from which the data are derived. Examples of the use of CBED techniques in measuring lattice parameters and strain are given from studies of precipitation (including misfit measurements) and from investigations of partially recrystallised microstructures. These examples are used to illustrate the advantages and limitations of the CBED technique.