I. Lonardelli

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.

Further evidence of tetragonality in bainitic ferrite

Abstract There is growing evidence that bainitic ferrite which retains a substantial amount of carbon in solid solution does not have cubic symmetry. We provide additional data on a different nanostructured bainitic steel to support this evidence, based on synchrotron X-ray diffraction experiments. The data are consistent only with a displacive transformation mechanism for bainite.

Fabric Development in a Middle Devonian Intraoceanic Subduction Regime: The Careon Ophiolite (Northwest Spain)

A Middle Devonian suprasubduction zone ophiolite, the Careón Unit (northwest Spain), displays amphibolite‐facies ductile deformation fabrics related to the onset of the Rheic Ocean closure. Two different fabrics, an early high‐T foliation and a subsequent lower‐T foliation, each of which characterized by distinct deformation mechanisms, have been identified in two distinct crustal‐scale shear zones of the same ophiolitic thrust sheet. Combined quantitative texture analysis by electron backscattered diffraction and time‐of‐flight neutron diffraction, were carried out on the shear zones and correlated with micro‐ and macrostructural data. The results indicate that the regional lineation and shear zone kinematics (east‐west, top‐to‐the‐east) represent fabrics developed essentially during the intraoceanic subduction of the Rheic Ocean, and their orientation may be considered a reference vector for convergence models in this part of the Variscan belt.

Determination of the crystal structure of nifedipine form C by synchrotron powder diffraction

The crystal structure of the metastable form C polymorph of nifedipine [C(17)H(18)N(2)O(6), 3,5-dimethyl 2,6-dimethyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate] was determined by means of direct-space techniques applied to high-resolution synchrotron powder diffraction data. The polymorph crystallizes in the space group P1 and exhibits a molecular packing significantly different from that of the stable modification, with molecules aligned in an orthogonal configuration inside the unit cell. The molecular conformation, on the other hand, remains substantially unmodified between the two polymorphs. Additionally, in situ thermal characterization of nifedipine crystallization behaviour was performed, confirming the nucleation of another metastable polymorph (form B) prior to the complete crystallization of the stable modification. A complete structural characterization of form B was not possible owing to its very limited stability interval.

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.

Nanostructured bainitic steel obtained by powder metallurgy approach: structure, transformation kinetics and mechanical properties

Abstract A PM approach is investigated in the context of extremely fine low temperature bainitic steels with a reasonable combination of ultimate tensile strength and uniform elongation. The strategy consists of three steps. First, ball milling is used for mechanical alloying and to create a large density of interfaces prior to sintering. In the second step, spark plasma sintering is used as a rapid consolidation process to retain a very fine and homogeneous structure after sintering. The isothermal heat treatment which leads to bainite can then be done at a low austenitisation temperature (860°C) for a few minutes, leading to a small initial austenite grain size. A fine grain size promotes the rapid transformation of the austenite into bainite. The characteristics of a nanostructured Fe–Ni–C bainitic steel obtained after mechanical alloying and nanostructuring of the powder, spark plasma sintering and final heat treatment are reported.

Research data supporting Experimental evidence for non-cubic bainitic ferrite

Data associated with syncrotron X-ray experiments conducted to show that the unit cell of bainitic ferrite is not cubic

Textural record of an intra-oceanic subduction: the Careón ophiolite (NW Spain)

The Subandean Basins of South America extending from Trinidad to Tierra del Fuego have been the object of intensive exploratory activities (Fig. 1). The largest amount of hydrocarbons discovered during the last 30 years in these basins was found in complex structural terrains. A total of 59 Billion Barrels of Oil Equivalent (BBOE) have been discovered in areas affected by compressional tectonics. Of these basins, the largest discoveries are in the Furrial Trend of Venezuela (24 BBOE), followed by the Chaco area in Bolivia and Argentina (13 BBOE), the Llanos Foothills of Colombia (4.4 BBOE), and the Madre de Dios Basin of Peru (4.2 BBOE).