X-ray diffraction analysis of substructures in plastically deformed BCC materials

A procedure for line-shape analysis of broadened X-ray (or neutron) diffraction peaks is presented and specified for b.c.c. materials, which takes into account the effect of interfaces, internal stress of the 2nd kind and a dislocation distribution with weak defect correlation. Application of the technique is demonstrated by the estimation of dislocation densities in plastically deformed α-iron and steel. The results confirm that X-ray line-broadening analysis is suitable for integrated substructure characterization, but it becomes also evident that local structural inhomogeneity and the texture of the sample material must carefully included into the interpretation of experimental data

X-ray determination of dislocation density and arrangement in plastically deformed copper

Using the kinematical theory of X-ray scattering by crystals with dislocations as developed by Krivoglazet al.and Wilkens, the dislocation content of compressed copper single and polycrystals was investigated by means of profile analysis of selected diffraction peaks. Measurements of radial intensity distributionsI(2θ) were performed with a double-crystal spectrometer in the case of the single crystals and with conventional polycrystal diffractometers in the case of the polycrystals. Additionally, the misorientations Θ occurring within the dislocation cell structure because of the accumulation of excess dislocations of one sign were investigated by means of rocking curves of the single-crystal reflections and by evaluation of electron backscattering patterns (EBSPs). Within a wide deformation range, the mean total dislocation density ρdcan be related well to the flow stressviathe Taylor relationship. Assuming a random distribution of the misorientations Θ between adjacent dislocation cells, the evaluation of the rocking curves gives mean values 〈|Θ|〉 much smaller than those determined by EBSP analysis. For this reason, a model of a dislocation cell structure with restrictedly correlated misorientations, which leads to better agreement of the X-ray and the EBSP data, is proposed.</jats:p

Compression Tests of Polycrystalline α-Iron up to High Strains Over a Large Range of Strain Rates

Compression tests have been performed on polycrystalline b.c.c. iron in order to study dynamic plasticity and evolution of microstructure. The paper describes the experimental setups and the results obtained at 295 K for strain rates 10-3s-1 ≤ dε/dt ≤ 104s-1 and plastic strains up to large values ε-0.8. Stress-strain diagrams have been found for all conditions mentioned. The rate dependence of stress indicates two regions of the rate sensitivity. The low strain rate range shows only slight rate sensitivity, but it increases rapidly at strain rates above 103s-1. This effect is accompanied by formation of twins. Optical and TEM micrographs confirm these observations. Dislocation density and micro-hardness have been also measured.Les essais de compression ont été effectués sur du fer polycristallin pour étudier la plasticité dynamique et l'évolution de microstructure. L'article décrit les bancs d'essais et les résultats obtenus à 295 K sur une grande plage de vitesse de déformation 10-3s-1 ≤ dε/dt ≤ 104s-1 et aux grands déformations ε-0.8. (jusqu'à ε-0.8.). Les courbes contrainte-déformation correspondantes ont été déterminées. La dépendance de la vitesse de déformation sur la contrainte indique deux régions de sensibilité à la vitesse. Le domaine de basses vitesses montre seulement une faible influence de la sensibilité à la vitesse, mais celle-ci augmente rapidement aux vitesses de déformation plus élevées au-delà de 104s-1. Cet effet est accompagné par la formation de macles. Les micrographies optiques et par MET confirment ces observations. La densité de dislocation et la micro dureté ont été aussi mesurées