Defect structure analysis of polycrystalline materials by computer-controlled double-crystal diffractometer with position-sensitive detector

Abstract

The method represents an extension of a previously developed X-ray double-crystal diffractometer method when a film was used to record the crystallite reflections, each reflecting crystallite being regarded as the second crystal of a double-crystal diffractometer. By utilizing a position-sensitive detector (PSD) with interactive computer controls, the tedious and limiting task of data acquisition and analysis is greatly simplified. The specimen is irradiated with crystalmonochromated radiation and the numerous microscopic spots emanating from the reflecting crystallites are recorded separately by the position-sensitive detector and its associated multichannel analyzer at each increment of specimen rotation. An on-line minicomputer simultaneously collects these data and applies the necessary corrections. This process is then automaticaIly repeated through the full rocking-curve range. The computer carries out the rocking-curve analysis of the individual crystallite reflections as well as that of the entire reflecting crystallite population. The instrument is provided with a specimen translation device which permits analysis of large sections of solid specimens. Thus, sites of local lattice defects induced either mechanically, chemically or by radiation can rapidly be established and quantitatively determined in terms of rocking-curve parameters as well as imaged by X-ray topography, by inserting a film in front of the PSD. The versatility and usefulness of the method is demonstrated by examples given from studies of fracture, fatigue and stress-corrosion cracking of commercial alloys.

Microstrain and Defect Analysis of CL-20 Crystals by Novel X-Ray Methods

“…XAPS is a suitable method for measuring the degree of imperfection and lattice misalignment of individual crystallite through X-ray rocking-curve half-width measurements [2,3,5,6].…”

“…Although some of these characteristics have been fairly well understood, the effects of more subtle features, such as molecular and crystal defects on the combustive properties of energetics, have not been investigated. The presence of microdefects such as misaligned domains and dislocations in single crystallites (particles) is known to increase their chemical activity, by straining the crystal lattice and making more reaction sites available at the domain boundaries and dislocation sites [2,3]. The strain energy of a dislocation is about 8 eV for each atom plane threaded by the dislocation, while the core energy is in the order of 0.5 eV per atom plane [4].…”

“…Yazici and D. Kalyon (XAPS), which is based on the simultaneous rocking-curve analysis of individual particles [2,3,5,6] was applied to CL-20 powders.…”

Following peak profiles during elastic and plastic deformation: A synchrotron-based technique

“…For example, the computer-aided x-ray double-crystal diffraction method, which uses a position sensitive detector to measure rocking curves of single grains, allows for a static mapping of micron level plasticity over a macrosized sample. 8,9 More recently a synchrotron-based in situ XRD method has been developed for determining the mechanical stress evolution in submicron thin films that are deposited on compliant substrates. 10 The technique comprises an initial "sin 2 " measurement to establish the absolute stress values followed by periodic "sin 2 " measurements during straining to determine the stress increments.…”