Crystallization kinetics of the bulk-glass-forming Pd43Ni10Cu27P20 melt

The crystallization of undercooled Pd43Ni10Cu27P20 melts is studied under isothermal conditions and at constant heating and cooling rates. Investigations are carried out by fluxing the melt with B2O3 and without any fluxing material. The isothermal experiments allow us to determine the complete time–temperature-transformation diagram with a minimum crystallization time of about 200 s for the fluxed melt and about 130 s for the unfluxed Pd43Ni10Cu27P20 melt. The results of the experiments at constant cooling and heating rates are summarized in a continuous heating and cooling diagram. The critical cooling rate for the fluxed alloy is determined to be 0.09 K/s, whereas the critical heating rate is 6 K/s. For the unfluxed Pd43Ni10 Cu27P20, 0.4 and 9 K/s are found, respectively. This alloy exhibits the most sluggish crystallization kinetics of all metallic systems known so far

Repeated crystallization in undercooled Zr41Ti14Cu12Ni10Be23 liquids

Isothermal crystallization studies are performed on Zr41Ti14Cu12Ni10Be23 melts. Undercooling experiments are carried out repeatedly at 907, 860, and 750 K. The scattering of the time to reach the onset of crystallization is investigated. Results from experiments performed at 907 K show a large scatter of the onset time of crystallization. For the experiments carried out at 860 and 750 K, scattering of the onset time is two orders of magnitude smaller. These results indicate that, at high temperatures, the crystallization is governed by the time scale of the statistical nucleation events. At low temperatures, the crystallization is controlled by diffusion, resulting in a well-defined onset time for crystallization

Pronounced asymmetry in the crystallization behavior during constant heating and cooling of a bulk metallic glass-forming liquid

The crystallization behavior of the supercooled bulk metallic glass-forming Zr41Ti14Cu12Ni10Be23 liquid was studied with different heating and cooling rates. A rate of about 1 K/s is sufficient to suppress crystallization of the melt upon cooling from the equilibrium liquid. Upon heating, in contrast, a rate of about 200 K/s is necessary to avoid crystallization. The difference between the critical heating and cooling rate is discussed with respect to diffusion-limited growth taking classical nucleation into account. The calculated asymmetry of the critical heating and cooling rate can be explained by the fact that nuclei formed during cooling and heating are exposed to different growth rates

Slow Atomic Motion in Zr-Ti-Cu-Ni-Be Metallic Glasses Studied by NMR

Nuclear magnetic resonance is used for the first time to detect slow atomic motion in metallic glasses, specifically, Be motion in Zr-Ti-Cu-Ni-Be bulk metallic glasses. The observations are not consistent with the vacancy-assisted and interstitial diffusion mechanisms and favor the spread-out free volume fluctuation mechanism for Be diffusion. Comparison with the results of Be diffusion measured by elastic backscattering the NMR results also indicates that the energy barriers for short- and long-range Be motion are the same

X-Ray Photon Correlation Spectroscopy Reveals Intermittent Aging Dynamics in a Metallic Glass

We use coherent X-rays to probe the aging dynamics of a metallic glass directly on the atomic level. Contrary to the common assumption of a steady slowing down of the dynamics usually observed in macroscopic studies, we show that the structural relaxation processes underlying aging in this metallic glass are intermittent and highly heterogeneous at the atomic scale. Moreover, physical aging is triggered by cooperative atomic rearrangements, driven by the relaxation of internal stresses. The rich diversity of this behavior reflects a complex energy landscape, giving rise to a unique type of glassy-state dynamics.Comment: 5 pages, 4 figure

Проект энергоблока АЭС повышенной маневренности

Выпускная квалификационная работа 132 с., 29 рисунков, 25 таблиц, 35 источников, 6 приложений. Ключевые слова: атомная станция, ядерный реактор, теплоноситель, насыщенный пар, парогенератор, паротурбинная установка. Объектом исследования является атомная станция с улучшенными характеристиками маневренности, предназначенная для генерации электрической и тепловой энергии в суточном графике регулирования Цель работы – оптимизация работы АЭС в режимах суточного регулирования. В процессе выполнения проекта проводились исследования экономического эффекта от внедрения гидромуфты на приводе питательных насосов. В результате исследования подтверждены ожидания экономического эффекта, определена экономия электрической энергии на собственные нужды.Graduation thesis 132 p., 29 figures, and 25 tables, 35 sources of, 6 applications. Key words: nuclear power station, nuclear reactor, coolant, saturated steam, steam generator, steam turbine. The object of study is the nuclear power plant with improved manoeuvrability, designed for generation of electric and thermal energy in a daily chart regulation The work purpose is optimization of NPP operation in the modes involved. In the process of implementation of the project was undertaken to study the economic effect of the introduction of the fluid coupling on the drive of feed pump. The study confirmed the expectations of economic benefits, identified savings of electric energy for own needs

Influence of process gas during powder bed fusion with laser beam of Zr-based bulk metallic glasses

Zr-based bulk metallic glasses offer a unique combination of hardness, high strength, and high elastic limits. Yet, manufacturable size and complexity are limited due to the required cooling rates. Short laser-material interaction times together with layer-wise and selective energy input allows the laser powder bed fusion process to largely overcome those restrictions. Still, the complex process-material interactions inhere numerous uncertainties. In the present work, additively manufactured Zr-based bulk metallic glasses produced under three different process gases are investigated by calorimetry, x-ray diffraction, and bending tests. A strong dependence between the thermophysical properties, flexural strength, and the applied atmosphere is found