General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. This paper extends our knowledge of the higher excited states of the ammonia molecule by presenting detailed measurements of the 2ϩ1 resonance enhanced multiphoton ionization ͑REMPI͒ spectrum of both NH 3 and ND 3 obtained following excitation in the wavelength range 298-242 nm, i.e., at energies up to the first ionization energy. Complementary analyses of the wavelength resolved REMPI spectrum and the accompanying REMPI-photoelectron spectra leads to the identification of ten new Rydberg origins of NH 3 ͑four for ND 3 ͒ with principal quantum numbers nр8 and, in most cases, of the accompanying out-of-plane bending vibrational progression. Symmetry assignments for the various newly identified excited states are offered, based on band contour simulation and/or quantum defect considerations. Dominant amongst these are the ẼЉThe present work serves to reinforce the previously noted dominance of np←1a 2 Љ Rydberg excitations in the 2ϩ1 REMPI spectrum of ammonia. In addition, the adiabatic ionization energy of ND 3 is estimated to be 82 280Ϯ40 cm Ϫ1 based on the assumption that analogous Rydberg states of NH 3 and ND 3 will have very similar quantum defects.
Despite much research into steels strengthened through interphase precitation, there remains much that is not clear, such as the role of a range of elements, particularly Mo, in the interphase precipitation process. Four steels were manufactured with identical composition, but with variations in Ti, V, Mo and N content to investigate the effect of composition on interphase precipitation. Alloys were rapidly cooled from the single austenite phase field and isothermally transformed at 630°C and 650°C for 90min. The addition of Mo was found to significantly reduce the austenite to ferrite transformation kinetics, particularly for the V steel. Interphase precipitation was observed in all alloys at both transformation temperatures. For the Ti bearing steel, the two types of precipitate were observed throughout the sample, namely TiC (finer) and Ti2C (coarser), while for the V bearing steels, VC (finer) and V4C3 (coarser) were observed. Where Mo was present in the alloy, it was found dissolved in all carbide types. The (Ti,Mo)C and (V,Mo)C formed by classical planer interphase precipitation (PIP) while the (Ti,Mo)2C and (V,Mo)4C3, that had a much wider row spacing, formed through curved interphase precipitation (CIP). Each adopted one variant of the Baker-Nutting orientation relationship. The Ti-microalloyed steels exhibited the smallest precipitates of all the steels, which were approximately the same size irrespective of whether Mo was present in the alloy and irrespective of the transformation temperature. However, the addition of Mo to the V bearing steels resulted in a significant increase in precipitate volume fraction and a reduction in precipitate size. The mechanisms of interphase precipitation leading to the coincident production of two different precipitate types is considered and the role of Mo on the interphase precipitation process is discussed. The resultant effect on strength is considered.
The precipitation kinetics of vanadium carbides and its interaction with the austenite-to-ferrite phase transformation is studied in two micro-alloyed steels that differ in vanadium and carbon concentrations by a factor of two, but have the same vanadium-to-carbon atomic ratio of 1:1. Dilatometry is used for heat-treating the specimens and studying the phase transformation kinetics during annealing at isothermal holding temperatures of 900, 750 and 650 °C for up to 10 h. Small-Angle Neutron Scattering (SANS) and Atom Probe Tomography (APT) measurements are performed to study the vanadium carbide precipitation kinetics. Vanadium carbide precipitation is not observed after annealing for 10 h at 900 and 750 °C, which is contrary to predictions from thermodynamic equilibrium calculations. Vanadium carbide precipitation is only observed during or after the austenite-to-ferrite phase transformation at 650 °C. The precipitate volume fraction and mean radius continuously increase as holding time increases, while the precipitate number density starts to decrease after 20 min, which corresponds to the time at which the austenite-to-ferrite phase transformation is finished. This indicates that nucleation and growth are dominant during the first 20 min, while later precipitate growth with soft impingement (overlapping diffusion fields) and coarsening take place. APT shows gradual changes in the precipitate chemical composition during annealing at 650 °C, which finally reaches a 1:1 atomic ratio of vanadium-to-carbon in the core of the precipitates after 10 h.
NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/. Publisher's statement:Please refer to the repository item page, publisher's statement section, for further information.For more information, please contact the WRAP Team at: wrap@warwick.ac.uk.Quasi in-situ analysis of geometrically necessary dislocation density in α-fibre and γ-fibre during static recrystallization in cold-rolled low-carbon Ti-V bearing microalloyed steel Abstract In the present study, cold-rolled low-carbon steel is annealed at three different conditions: 700 o C for 0 s, 800 o C for 0 s and 800 o C for 2 min at the heating rate of ~10 o C/s. Recrystallization behaviour on sample surface is studied using a heated stage Scanning Electron Microscopy and Electron Backscattered Diffraction. For the lower annealing temperature of 700 o C with no dwell, almost no recrystallization is observed and microstructure resembles the as-received deformed material with the exception of occasional sub-micron sized nuclei. For the annealing conditions of 800 o C 0 s and 800 o C 2 min, onset and evolution of recrystallization is observed in-situ as a function of the initial as-cold rolled texture. Slower recovery rate of alpha fibre than gamma fibre is observed and confirmed by lower drop in average geometrically necessary dislocation (GND) density for un-recrystallized alpha fibres(1.1E+14 m -2 for 700 o C 0 s , 1.4E+14 m -2 for 800 o C 0 s and 4.5E+14 m -2 for 800 o C 2 min) than for un-recrystallized gamma fibre grains (3.0E+14 m -2 for 700 o C 0 s , 6.2E+14 m -2 for 800 o C 0 s and 9.8E+14 m -2 for 800 o C 2 min) during annealing. Strong gamma texture in recrystallized matrix is found for annealing conditions of 800 o C 0 s and 800 o C 2 min. From TEM characterisation it was shown that sub-grain boundaries are decorated with fine precipitates (diameter d < 15 nm) of titanium-vanadium carbides (Ti,V)C for the annealing condition of 700 o C 0 s, which suggests that these precipitates play a major overall role in retardation of the recrystallization kinetics.
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