Effect of crystallite orientation and external stress on hydride precipitation and dissolution in Zr2.5%Nb

Thermal cycling of Zr2.5%Nb pressure tubes specimens containing ∼100 wt ppm H between room temperature and 400 °C produces the dissolution and re-precipitation of zirconium hydride, with a distinctive hysteresis between these two processes. In this work, we have found that the details of the precipitation and dissolution depend on the actual orientation of the α-Zr grains where hydride precipitation takes place. In situ synchrotron X-ray diffraction experiments during such thermal cycles have provided information about hydride precipitation specific to the two most important groups of α-Zr phase orientations, namely crystallites having c-axes parallel (mHoop) and tilted by ∼20° (mTilted) from the tube hoop direction. The results indicate that hydrides precipitate at slightly higher temperatures (∼5 °C), and dissolve at consistently higher temperatures (∼15 °C) in mTilted grains than in mHoop grains. Moreover, application of a tensile stress along the tube hoop direction results in two noticeable effects in hydride precipitation. Firstly, it shifts hydride precipitation towards higher temperatures, at a rate of ∼(0.08 ± 0.02) °C/MPa for hydrides precipitated in the mHoop grains. Secondly, it produces a redistribution of hydrogen between grains of different orientations, increasing hydride precipitation on those α-Zr grains having their c-axes stretched by the external load. A detailed analysis of the diffracted signal shows that such redistribution occurs during the precipitation stage, as a result of changes in the precipitation temperatures for different grain orientations.Fil: Vizcaino, Pablo. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Santisteban, Javier Roberto. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Vicente Alvarez, Miguel Angel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Banchik, Abraham David. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Almer, J.. Argonne National Laboratory; Estados Unido

Terminal solid solubility determinations in the H–Ti system

The terminal solid solubility of hydrogen in titanium was measured by differential scanning calorimetry in the concentration range of 0.3–4.1 at.% which practically corresponds to the whole solubility range of hydrogen in α-Ti. The solvus enthalpy obtained in this range from the overall data set was 22.8 ± 0.5 kJ/molH. However, a more careful analysis of the experimental results shows that the solubility curve has two different behaviors as a function of concentration. In the high concentration range 1.4–4.1 at.% a solvus enthalpy of 29.0 ± 1.5 kJ/molH was obtained representing the α/α + δ equilibrium boundary. In the low concentration range, 0.3 at.% to 1.4 at.%, the slope was noticeably lower with 24.2 ± 1.5 kJ/molH for the solvus enthalpy. This last value should correspond to the [α]/[α + γ] equilibrium curve. Although it is possible this value might be influenced by the presence of tiny amounts of the now metastable δ phase–as its presence is revealed by X-ray diffraction analysis – anyway it is consistent with a α + δ ↔ γ peritectoid reaction temperature of 168 °C obtained from the literature. The eutectoid α + δ ↔ β decomposition temperature was determined using samples of high hydrogen contents, ranging from 9 to 11.0 at.%. This temperature was determined to be 319.9 ± 1 °C from the analysis of the DSC diagrams. The solubility limit [α]/[α + δ] at this eutectoid reaction was estimated to be 5.44 ± 0.27 at.%. The present results are believe to provide a closer approximation to the solubility values of H in α-Ti as presently reported in the literature.Fil: Vizcaino, Pablo. Universidad Nacional de La Matanza; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lopez Vergara, I. A.. Universidad Nacional de La Matanza; ArgentinaFil: Banchik, Abraham David. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Abriata, Jose Pablo. No especifica

Effect of crystallite orientation and external stress on hydride precipitation and dissolution in Zr2.5%Nb

Thermal cycling of Zr2.5%Nb pressure tubes specimens containing ∼100 wt ppm H between room temperature and 400 °C produces the dissolution and re-precipitation of zirconium hydride, with a distinctive hysteresis between these two processes. In this work, we have found that the details of the precipitation and dissolution depend on the actual orientation of the α-Zr grains where hydride precipitation takes place. In situ synchrotron X-ray diffraction experiments during such thermal cycles have provided information about hydride precipitation specific to the two most important groups of α-Zr phase orientations, namely crystallites having c-axes parallel (mHoop) and tilted by ∼20° (mTilted) from the tube hoop direction. The results indicate that hydrides precipitate at slightly higher temperatures (∼5 °C), and dissolve at consistently higher temperatures (∼15 °C) in mTilted grains than in mHoop grains. Moreover, application of a tensile stress along the tube hoop direction results in two noticeable effects in hydride precipitation. Firstly, it shifts hydride precipitation towards higher temperatures, at a rate of ∼(0.08 ± 0.02) °C/MPa for hydrides precipitated in the mHoop grains. Secondly, it produces a redistribution of hydrogen between grains of different orientations, increasing hydride precipitation on those α-Zr grains having their c-axes stretched by the external load. A detailed analysis of the diffracted signal shows that such redistribution occurs during the precipitation stage, as a result of changes in the precipitation temperatures for different grain orientations.Fil: Vizcaino, Pablo. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Santisteban, Javier Roberto. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Vicente Alvarez, Miguel Angel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Banchik, Abraham David. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Almer, J.. Argonne National Laboratory; Estados Unido

Typische Mikrostrukturen von Zirconiumlegierungen in Komponenten kerntechnischer Anlagen

The different microstructures typically found in nuclear components made of zirconium alloys are discussed in this paper. These include material in a variety of thermo-mechanical conditions, e.g., cold rolled, stress relieved, recrystallized, welded, biphasic, together with minority second phases belonging to the original material or incorporated due to in-service conditions. The anisotropic crystalline structure of zirconium is exploited in microscopical observations by means of polarizer filters that enhance the contrast between different grains, and greatly aid the identification in most microstructures. Most microstructural variations across a wide range of length-scales, such as those produced by welding processes, can be effectively resolved by traditional optical microscopy (OM). However, some finer microstructures like those found in CANDU1 (CANada Deuterium Uranium) reactor pressure tube material, or some minority second phase particles like the Zr(Fe,Cr)2 precipitates in Zircaloy-4 cannot be completely resolved by this technique. Thus, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are required in such cases. For SEM observations we show the valuable issue of the scale in specific microstructural studies, which allows quantifying microstructural parameters using image analysis. For TEM observations, we have greatly benefited from the electron diffraction diagrams, which have allowed us to investigate the crystalline structure of irradiated second phase particles, which would remain unnoticed to both, OM or SEM observations.Diese Arbeit beschäftigt sich mit den unterschiedlichen, in Komponenten kerntechnischer Anlagen aus Zirconiumlegierungen typischerweise auftretenden Mikrostrukturen. Dabei handelt es sich um Werkstoffe mit verschiedenen, durch thermomechanische Behandlung herbeigeführten Zuständen, z.B. kaltgewalzt, spannungsarm geglüht, rekristallisiert, geschweißt, zweiphasig nebst sekundären Minoritätsphasen, die zum Originalwerkstoff gehören oder aufgrund der Betriebsbedingungen enthalten sind. Die anisotrope Kristallstruktur von Zirconium wurde in mikroskopischen Betrachtungen mittels Polarisationsfiltern ausgewertet, die den Kontrast zwischen unterschiedlichen Körnern verstärken und bei der Identifizierung der meisten Mikrostrukturen eine große Hilfe sind. Die meisten mikrostrukturellen Varianten, wie beispielsweise solche, die durch Schweiß­ vorgänge entstehen, können in einer großen Bandbreite von Längenskalen anhand der traditionellen optischen Mikroskopie (OM) effizient aufgelöst werden. Einige feinere Mikrostrukturen, wie solche, wie sie im Druckröhrenwerkstoff des CANDU-Reaktors1 (CANada Deuterium Uranium) auftreten, oder einige sekundäre Minoritätsphasenpartikel wie die Zr(Fe,Cr)2-Ausscheidungen in Zircaloy-4 können anhand dieser Technik nicht vollständig aufgelöst werden. Daher ist in solchen Fällen der Einsatz von Rasterelektronenmikroskopie (REM) und Transmissionselektronenmikroskopie (TEM) erforderlich. Wir beschäftigen uns auf der Basis von REM-Betrachtungen mit dem wichtigen Thema der Skalierung bei bestimmten Mikrostrukturuntersuchungen, durch die Mikrostrukturparameter mittels Bildanalyse quantitativ erfasst werden können. Bei den TEM-Betrachtungen waren uns die Elektronenbeugungsdiagramme sehr nützlich. Sie haben es uns ermöglicht, die Kristallstruktur der bestrahlten Sekundärphasenpartikel zu untersuchen, die sowohl im OM als auch bei einer Betrachtung im REM unbemerkt bleiben würden.Fil: Flores, A. V.. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Gomez, A. G.. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Juarez, Gabriel Alejandro. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Loureiro, N.. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Samper, R. I.. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Santisteban, Javier Roberto. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche. Laboratorio de Neutrones y Reactores; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Vicente Alvarez, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche. Laboratorio de Neutrones y Reactores; ArgentinaFil: Tolley, Alfredo Juan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche. División Metales; ArgentinaFil: Condo, Adriana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche. División Metales; ArgentinaFil: Bianchi, R. D.. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Banchik, Abraham David. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; ArgentinaFil: Vizcaino, Pablo. Comisión Nacional de Energía Atómica. Centro Atómico Ezeiza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin