Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
- 2019 (116) (entfernen)
Dokumenttyp
- Posterpräsentation (116) (entfernen)
Referierte Publikation
- nein (116)
Schlagworte
- Additive Manufacturing (10)
- Additive manufacturing (5)
- Boehmite (5)
- Glass (5)
- Nanoparticles (5)
- 316L (4)
- Catalysis (4)
- Computed Tomography (4)
- Computed tomography (4)
- Corrosion (4)
Organisationseinheit der BAM
- 6 Materialchemie (42)
- 5 Werkstofftechnik (28)
- 8 Zerstörungsfreie Prüfung (27)
- 8.5 Röntgenbildgebung (17)
- 6.6 Physik und chemische Analytik der Polymere (16)
- 9 Komponentensicherheit (16)
- 6.3 Strukturanalytik (11)
- 9.3 Schweißtechnische Fertigungsverfahren (9)
- 5.1 Mikrostruktur Design und Degradation (8)
- 1 Analytische Chemie; Referenzmaterialien (7)
- 4 Material und Umwelt (7)
- 8.0 Abteilungsleitung und andere (7)
- 1.2 Biophotonik (6)
- 5.6 Glas (6)
- 6.1 Oberflächen- und Dünnschichtanalyse (6)
- 6.7 Materialsynthese und Design (6)
- 7 Bauwerkssicherheit (6)
- 5.2 Metallische Hochtemperaturwerkstoffe (5)
- 5.4 Multimateriale Fertigungsprozesse (5)
- 2 Prozess- und Anlagensicherheit (4)
- 5.3 Polymere Verbundwerkstoffe (4)
- 6.2 Material- und Oberflächentechnologien (4)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (4)
- 9.4 Integrität von Schweißverbindungen (4)
- 4.5 Kunst- und Kulturgutanalyse (3)
- 6.5 Synthese und Streuverfahren nanostrukturierter Materialien (3)
- 8.4 Akustische und elektromagnetische Verfahren (3)
- 2.0 Abteilungsleitung und andere (2)
- 2.1 Sicherheit von Energieträgern (2)
- 3 Gefahrgutumschließungen; Energiespeicher (2)
- 4.1 Biologische Materialschädigung und Referenzorganismen (2)
- 4.2 Material-Mikrobiom Wechselwirkungen (2)
- 5.5 Materialmodellierung (2)
- 7.1 Baustoffe (2)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (2)
- 9.5 Tribologie und Verschleißschutz (2)
- 1.9 Chemische und optische Sensorik (1)
- 3.1 Sicherheit von Gefahrgutverpackungen und Batterien (1)
- 3.2 Gefahrguttanks und Unfallmechanik (1)
- 4.0 Abteilungsleitung und andere (1)
- 8.6 Faseroptische Sensorik (1)
- 9.0 Abteilungsleitung und andere (1)
Over the past decades research on the molecular dynamics of miscible polymer blends is of topical interest in the literature, to understand the segmental mobility of individual components, as it is affected by blending. In general, miscible polymer blends exhibit a complex dynamic behavior. For an A/B blend the relaxation times of component A and component B are affected by the spatial local compositional heterogeneity, present in binary systems on a microscopic level, regardless of the macroscopic homogeneity. Here, a combination of broadband dielectric and specific heat spectroscopy was employed to study the dynamically asymmetric PVME/PS blend with seven different compositions, focusing on samples with high PS contents. Considering that PS is dielectrically invisible, BDS is a powerful technique to study the response of PVME, as it is affected by PS segments. Here, three separate relaxation processes were found by dielectric investigations, related to confined or constrained PVME segments due to the spatial local compositional heterogeneities, which is in contrary to the previous literature findings [1]. Moreover, the dielectric data was compared with results obtained by specific heat spectroscopy, where a fourth relaxation process was found, due to the cooperative fluctuations of PVME and PS.
[1] Colmenero, J., Arbe, A. Soft Matter, 2007, 3, 1474.
Thermodynamic study of a refractory complex concentrated alloy (rCCA) using the CALPHAD method
(2019)
Multi-principal-element alloys (MPEAs), have recently come to the attention of the scientific community due to their potential for improving properties such as, e.g. mechanical strength and oxidation resistance in high temperature structural applications. The AlMo0.5NbTa0.5TiZr refractory (r)CCA is one such candidate, showing a two-phase microstructure after a two-stage heat treatment under argon atmosphere at a controlled cooling rate. Since the application conditions intended for this alloy require a long-term high temperature (> 700 °C) mechanical and oxidation resistance, it becomes necessary to assess the possible phase development in this regime. The diagrams reveal that two BCC-based phases could form during alloy solidification, where one phase would be enriched with Mo, Nb and Ta while the other phase, with Al, Ti and Zr. Activity oxides diagrams show that a stable form of aluminum oxide (α-Al2O3, Pearson symbol: hR10, corundum) can be formed.
Introduction/purpose:
Multi-principal-element alloys (MPEAs), also known as complex concentrated alloys (CCAs), have recently come to the attention of the scientific community due to some interesting and unexpected microstructures, and their potential for improving properties such as, e.g. mechanical strength and oxidation resistance in high temperature structural applications. The AlMo0.5NbTa0.5TiZr refractory (r)CCA is one such candidate, showing a two-phase microstructure after a two-stage heat treatment under argon atmosphere at a controlled cooling rate. Since the application conditions intended for this alloy require a long-term high temperature (> 700 °C) mechanical and oxidation resistance, it becomes necessary to assess the possible phase development in this regime.
Methods:
In this contribution, the CALPHAD method is used to calculate phase equilibria for the AlMo0.5NbTa0.5TiZr CCA in the presence and absence of oxygen. Equilibrium phase amount evolution with temperature and Scheil Model for solidification (e.g. Fig.1a and Fig.1b, respectively) are analyzed, which are obtained using the databases TCNI9 and TTNI7 and the Gibbs energy minimizer in the Thermo-Calc software.
Results:
The diagrams reveal that two BCC-based phases could form during alloy solidification, where one phase would be enriched with Mo, Nb and Ta while the other phase, with Al, Ti and Zr. Activity oxides diagrams show that a stable form of aluminum oxide (α-Al2O3, Pearson symbol: hR10, corundum) can be formed. Results obtained by both databases, as well as discrepancies between property phase and Scheil approaches are discussed on the base of experimental results.
Conclusions:
A modeling tool is used to support alloy characterization and development, providing also the possibility to feedback information to improve existing thermodynamic databases.
Fresh cement paste is a suspension consisting of a hydraulic binder (cement), water, and numerous minor components – admixtures. Addition of admixtures aims at specific modification of properties of the fresh cement paste or hardened cementitious building material. Specific admixtures, so-called superplasticizers (SP), are used to improve the flowability of the fresh cement paste with reduced water content. The latter is the starting material for the high-strength concrete. Thus, SPs are essential for the ambitious construction projects.
However, uncontrollable retardation of the setting time in presence of SPs is occasionally observed. Obviously, SPs influence early products of the cement hydration leading to changes in the microstructure development. The hardening is thus delayed, and the quality of the resulting building material suffers. The mechanisms of the admixture action during the hydration process are still intensively investigated [1-7]. A detailed understanding of the admixture effects during the early hydration stage is the key to control and individual adjustment of the cement-based construction materials.
We use the unique combination of the wall-free sample holder and the time-resolved X-ray scattering analysis to achieve the full information about the hydrate phases formed under the influence of admixtures. We use ultrasonic levitator to start the cement hydration in levitated cement pellets [8, 9]. The sample levitation allows collection of the unimpaired information about cement hydrate phases. The most beneficial is the avoiding of the contributions of the sample holder material to the data signal.
We induce the cement hydration by adding water to unhydrated Portland cement during the data acquisition. The full phase composition of the hydrating cementitious system can be gathered in situ using wide angle X-ray scattering (WAXS). During the hydration of cement both crystalline and amorphous hydrate phases are formed. WAXS data contain the information about crystalline phases behind the Bragg reflections, whereas the amorphous hydrates influence the appearance of the background. Application of the data analysis specific for crystalline or amorphous phases is needed. The data quantification by the Rietveld method allows to conclude about the changes of the phase amounts due to the presence of admixture. The calculation of the pair distribution functions allows analysis of the amorphous hydrates. Based on this information, the SP effects and the extent of their involvement into the ongoing reactions can be concluded. A detailed understanding of the complex cement hydration process is envisioned.
During the last years Additive Manufacturing (AM) became increasingly important. That becomes clear, while looking at the advantages like a high degree of freedom concerning the geometry of the parts, low waste rates and a reduction of postprocessing, to name just three. Laser Metal Deposition (LMD) is one of those AM- methods. It can be used for different kinds of applications, e.g. repair weldings of used parts, coatings to increase the corrosion resistance or to build up new components. But for all applications, the production of defect free parts is crucial. Therefore, different kinds of non-destructive monitoring techniques were tested for the LMD-process to identify their potential to detect imperfections in-situ.
The environmental pollution with plastic debris is one of the great challenges scientists are facing in recent times Due to degradation by UV radiation and other environmental factors, larger pieces of plastic can decompose into microscale fragments which can enter human foodstuff through the food chain or by environmental entry Recent publications show a contamination of various food products with microplastic particles suggesting a widespread exposure Thus, orally ingested plastic particles pose a potential health risk to humans In this study, we investigated the impact of artificial digestive juices on the size and shape of the three environmentally relevant microplastic particles polystyrene (PS), polypropylene (PP) and polyvinyl chloride (PVC).
The life time of mechanical components in high temperature applications is basically determined by their workings. Corrosion determines the loss of material corresponding to the loss of the effective load-bearing section and consequently increasing stress levels. To improve the material selection for such applications a numerical life prediction corrosion model for different alloys and environments is needed. Based on the ferritic alloys FeCr and FeCrCo a first quantitative model is to be developed. For this purpose, the alloys are aged at 600°C, 650°C and 700°C in synthetic air under normal pressure for between 10 and 240 hours. The first objective is to establish a quantitative relationship between the oxidation rate as a function of composition and microstructure of the alloys. The influence of the inner interface as an essential parameter for transport by diffusion on the oxidation kinetics is discussed in this presentation.
In special cases of angle beam ultrasonic measurement the applied transducer has to withstand extreme temperatures. Since the irradiation angle depends on the speed of sound in both the wedge material and the tested object, the developer must take into account the speed of Sound in a wedge material over the whole temperature range of transducers application.