ReX.Cell: a user-friendly program for powder diffraction indexing

ReX.Cellis a novel software package dedicated to the automation of crystal cell indexing starting from powder diffraction data. The program aims to help both novice and experienced powder diffractionists overcome the practical difficulties encountered during powder data indexing, by offering a user-friendly highly interactive interface to classical indexing engines. The software provides a wizard-style approach, accompanying the user through all the typical steps of the indexing procedure: preliminary data processing, background subtraction, data smoothing, peak finding and finally autoindexing. Each step can be carried out automatically or fine-tuned through custom options; in either mode, algorithms and filters are applied in real time to the diffraction data, giving an immediate visual feedback. The program is written in the Java programming language and runs on several different operating systems; source code is provided to allow developers to add support for additional indexing programs and/or powder diffraction data formats.</jats:p

ReX: a computer program for structural analysis using powder diffraction data

Multi-platform software has been developed for the analysis of powder diffraction data, with particular focus on structure solution. The program provides a Rietveld optimization engine, with the possibility of refining parameters describing both the sample and the instrument model. Geometric constraints such as rigid fragments and torsion angles can be defined for the atomic structure, to reduce the number of degrees of freedom of the model. An innovative hierarchical description of the asymmetric unit has been adopted, which allows, in principle, the definition of arbitrarily complex geometric relationships. Additionally, global optimization algorithms may be used in place of the standard nonlinear least squares, when particularly challenging problems are being faced

On the Formability and Microstructural Characteristics of AISI 301 Parts Formed by Single-Point Incremental Forming

The present work focuses on the correlation between the material tendency to be deformed by incremental sheet forming and the microstructural features that appear during the process itself. The material object of the study is the stainless steel AISI 301L. Single-point incremental forming (SPIF) experiments were carried out and the material formability evaluated. X-ray diffraction (XRD) analysis was utilized to determine the fraction of transformed martensite along the wall of formed parts at different levels of thickness reduction. TEM analysis was then employed to analyze the microstructure developed during the SPIF process. Two fundamental deformation mechanisms are observed, which could explain the remarkable material formability achievable during the SPIF process: strain induced martensitic transformation, and deformation twinning. Particularly, deformation twinning (instead of dislocation slip) appears to be the preferred plastic deformation mode of austenite at the early stage of the process, leading to the formation of multiple nano-twins in coarse grains that are responsible for the material ductility enhancement

Texture changes in the hcp -&gt; bcc -&gt; hcp transformation of zirconium studied in situ by neutron diffraction

Abstract The crystallographic texture of hot-rolled polycrystalline zirconium has been studied below and above the hcp-bcc transition temperature with HIPPO, the new time-of-flight neutron diffractometer at Los Alamos Neutron Science Center, making use of the multidetector capabilities and a vacuum furnace. Incomplete pole figures were extracted from diffraction spectra to determine the orientation distribution function and recalculate complete pole figures in situ at various temperatures. The texture analysis reveals that the orientation of grains in the new high-temperature (bcc) phase is related to the texture of the low-temperature (hcp) phase by Burgers relation, but with both an orientation selection and a symmetry variant selection. The cubic transformation texture is best explained if we assume preferential nucleation of the bcc phase in the hcp grain orientations that are most subject to mechanical twinning. After cooling, the new hcp texture closely resembles the original texture. Thermal cycling repeats this process with slight strengthening of the texture. The hexagonal transformation texture (after cooling) may be caused by nucleation and growth of untransformed domains or through variant selection by stresses imposed by neighboring grains