Texture Variations and Cyclic Softening Mechanisms on ZRY-4 at Room Temperature. Part I: Cyclic behavior

RESUMEN El presente trabajo informa sobre experimentos de fatiga, y su correspondiente interpretación, efectuados en Zry-4 con el objeto de estudiar los fenómenos de ablandamiento cíclico que este material presenta a temperatura ambiente. El endurecimiento cíclico es un fenómeno habitual en materiales recocidos en tanto que fenómenos de reacomodamiento de defectos pueden dar lugar a ablandamiento en deformación cíclica en materiales endurecidos por deformación previa. Estos fenómenos se encuentran bastante bien estudiados en materiales de estructura FCC y BCC. En el caso de materiales HCP, como las aleaciones de Zr y Ti, la información existente es mucho más escasa. El principal propósito es analizar la confiabilidad de modelos que pretenden explicar estos fenómenos de ablandamiento como efecto de reorientaciones cristalinas inducidas por la deformación cíclica. Ha sido propuesto que esta reorientación, o cambio en la textura del material, produciría un ablandamiento debido a la disminución del factor de Taylor por reorientación de planos de deslizamiento prismático. La Parte I del trabajo presenta, además de los ensayos de fatiga, un análisis y modelos alternativos de interpretación de los resultados. La Parte II presenta experimentos de medición de texturas, además de ensayos de fatiga complementarios, y simulaciones mediante modelos auto consistentes que permiten evaluar el comportamiento en fatiga de las distintas texturas medidas. Palabras clave: Fatiga de bajo número de ciclos, difracción de rayos x, textura, modelos micro mecánicos, ablandamiento cíclico. ABSTRACT The current paper presents fatigue experiments, and its interpretations, performed in Zry-4 to study cyclic softening behavior shown by this material at room temperature. Cyclic hardening is a usual phenomena in well-annealed materials while defect re-arrangement phenomena can lead to cyclic softening in previously deformation hardened materials. These phenomena are well studied in FCC and BCC materials. For HCP materials, like Zr and Ti alloys, the current information is much more scanty. The main purpose of the current paper is the analysis of the reliability of some models proposing crystal reorientation during cyclic deformation as the main cause for cyclic softening. According to those models, that reorientation, or texture change, would induce softening due to diminishing Taylor factors because of prismatic slip system rotations. Part I of the paper presents, besides fatigue tests, analysis of the results and alternative models for interpretation. Part II shows texture experiments, together with complementary fatigue experiments, and selfconsistent micromecanical simulations to evaluate expected fatigue behavior of the measured textures

Combined materials characterization by area detector investigations using hard X-rays

Materials characterization includes a long list of information’s which are on one hand important for process optimizations and on the other hand key knowledge for application, lifetime and failure predictions. With the help of area detector investigations one is able to get simultaneously all information related to line position, line intensity and line broadening of Bragg reflections. Examples are residual stress profiles, quantitative texture mapping, diffraction elastic constants, lattice dependent stress-strain curves, thermal expansion coefficients and defect densities. A very special case is high energetic synchrotron radiation which allows very fast and complete detection of generalized pole figures, namely intensity pole figures (texture), line broadening pole figures (micro-strain) and line position pole figures (macro-strain) using complete Debye-Scherrer rings

Long-term microstructural stability of oxide-dispersion strengthened Eurofer steel annealed at 800ºC

Oxide-dispersion strengthened ferritic martensitic steels such as ODS-Eurofer grade are good candidates for structural applications in future fusion power reactors. Long-term annealing treatments in vacuum were carried out in cold-rolled samples (80% reduction in thickness) from 1 h up to 4320 h (6 months) at 800 °C, i.e. the maximum temperature in the ferritic phase field, to follow its softening behavior. The microstructural stability of this steel was mapped using several characterization techniques including scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, Vickers microhardness testing, X-ray diffraction texture measurements, low-temperature electrical resistivity, and magnetic coercive field measurements. ODS-Eurofer steel displays good microstructural stability. Discontinuous recrystallization occurs at the early stages of annealing resulting in a low volume fraction of recrystallized grains. Extended recovery is the predominant softening mechanism at this temperature for longer times.Fil: Zilnyk, K. D.. Universidade de Sao Paulo; BrasilFil: Samdim, H. R. Z.. Universidade de Sao Paulo; BrasilFil: Bolmaro, Raul Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); ArgentinaFil: Lindau, R.. Karlsruher Institut Fur Technologie; AlemaniaFil: Möslang, A.. Karlsruher Institut Fur Technologie; AlemaniaFil: Kostka, A.. Max-Planck Institut für Eisenforschung; AlemaniaFil: Raabe, D.. Max-Planck Institut für Eisenforschun; Alemani