Formation and subdivision of deformation structures during plastic deformation.

During plastic deformation of metals and alloys, dislocations arrange in ordered patterns. How and when these self-organization processes take place have remained elusive, because in situ observations have not been feasible. We present an x-ray diffraction method that provided data on the dynamics of individual, deeply embedded dislocation structures. During tensile deformation of pure copper, dislocation-free regions were identified. They showed an unexpected intermittent dynamics, for example, appearing and disappearing with proceeding deformation and even displaying transient splitting behavior. Insight into these processes is relevant for an understanding of the strength and work-hardening of deformed materials.

Quantitative high-pressure pair distribution function analysis.

The collection of scattering data at high pressure and temperature is now relatively straightforward thanks to developments at high-brightness synchrotron radiation facilities. Reliable data from powders, that are suitable for structure determination and Rietveld refinement, are routinely collected up to about 30 GPa in either a large-volume high-pressure apparatus or diamond anvil cell. In those cases where the total elastic scattering is of interest, as it is in the case of nano-crystalline and glassy materials, technical developments, including the use of focused high-energy X-rays (>80 keV), are advantageous. Recently completed experiments on nano-crystalline materials at the 1-ID beamline at the Advanced Photon Source suggest that quantitative data, suitable for pair distribution function analysis, can be obtained.

Probing local and long-range structure simultaneously: an in situ study of the high-temperature phase transition of alpha-AlF3.

We show in this Communication that the combination of Rietveld and pair distribution function (PDF) analyses allows unique insight into the nature and driving force of the phase transition of alpha-AlF3, which was not available from conventional structural analysis methods alone. The use of image plate technology allows structural changes to be followed in "real time" and reduces the time required to collect high-resolution PDF data from hours (with a conventional solid state detector) to seconds. This methodology produces raw data that can simultaneously be analyzed by both Rietveld and PDF analysis.