5 Werkstofftechnik
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- 2018 (73) (entfernen)
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- Zeitschriftenartikel (73) (entfernen)
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- Residual stress (6)
- Additive manufacturing (4)
- 3D-Printing (3)
- Creep (3)
- EBSD (3)
- High temperature corrosion (3)
- Microstructure (3)
- Additive Manufacturing (2)
- Aging (2)
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Organisationseinheit der BAM
- 5 Werkstofftechnik (73) (entfernen)
Effects of various geometrical and physical factors, as well as the method of data reduction (analysis of
experimental forceedisplacement curves) on the values of local interfacial strength parameters (local IFSS, td, and critical energy release rate, Gic) determined by means of a single fiber pull-out test are discussed. Experimental results of our pull-out tests on several fiberepolymer matrix systems showed that td and Gic weakly depended on geometrical factors. However, the pull-out test appeared to be sensitive to the conditions of specimen formation and testing, such as changing the nature of the contacting surfaces (fiber sizing) and the fiber pull-out rate. Of several methods of td and Gic Determination from a forceedisplacement curve, the most reliable and reproducible one is the approach based on the values of the maximum force recorded in a pull-out test and the interfacial frictional force immediately after fiber debonding.
Technically relevant P92 steel (9% Cr) was coated with a micron-thick porous alumina layer prepared by sol-gel technique and treated with flue gas (60 CO2-30 H2O-2 O2-1 SO2-7 N2 (mole fraction in %)) at 650 ° to mimic an oxyfuelcombustion process. Local defects in the coating were marked using focused ion beam (FIB) technique and were inspected after exposition to hot flue gas atmosphere at 300, 800, and 1300 h, respectively. Local defects like agglomerated alumina sol particles tend to spall off from the coating uncovering the underlying dense chromia scale. Re-coating was found to restore the protection ability from oxidation when repeatedly treated with hot flue gas. Cracks and voids did not promote the local oxidation due to the formation of crystalline Mn/S/O species within and on top of the coating. The protective character of the steel-coating system is a result of (i) the fast formation of a dense chromia scale at the surface of sol-gel alumina-coated P92 steel bars in combination with (ii) the porous alumina coating acting as diffusion barrier, but also as diffusion partner in addition with (iii) fast Mn outward diffusion capturing the S species from flue gas.
A glass of the composition 37BaO·16CaO·47SiO2 wt% produced on an industrial scale is crystallized at 970 °C for times ranging from 15 min to 2 h. The crystallization at the immediate surface as well as the crystal growth into the bulk are analyzed using scanning electron microscopy (SEM) including energy dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD) as well as X-ray diffraction in the Θ–2Θ setup (XRD). The immediate surface shows the oriented nucleation of walstromite as well as the formation of wollastonite and an unknown phase of the composition BaCaSi3O8. All three phases also grow into the bulk where walstromite ultimately dominates the kinetic selection and grows throughout the bulk due to a lack of bulk nucleation. Walstromite shows systematic orientation changes as well as twinning during growth. A critical analysis of the XRD-patterns acquired from various crystallized samples indicates that their evaluation is problematic and that phases detected by XRD in this system should be verified by another method such as EDXS.
We describe a lattice-based crystallographic approximation for the analysis of distorted crystal structures via Electron Backscatter Diffraction (EBSD) in the scanning electron microscope. EBSD patterns are closely linked to local lattice parameter ratios via Kikuchi bands that indicate geometrical lattice plane projections. Based on the transformation properties of points and lines in the real projective plane, we can obtain continuous estimations of the local lattice distortion based on projectively transformed Kikuchi diffraction simulations for a reference structure. By quantitative image matching to a projective transformation model of the lattice distortion in the full solid angle of possible scattering directions, we enforce a crystallographically consistent approximation in the fitting procedure of distorted simulations to the experimentally observed diffraction patterns. As an application example, we map the locally varying tetragonality in martensite grains of steel.
Werkstoffe im Hochtemperatureinsatz verändern mit der Zeit ihre Mikrostruktur. Mit diesem Alterungsprozess einher geht eine Veränderung der mechanischen Eigenschaften ebenso wie eine Veränderung des Schädigungsverhaltens. Im Rahmen des FVV Vorhabens „Alterung und Lebensdauer“ haben das Fraunhofer IWM in Freiburg und die BAM in Berlin die weit verbreitete warmfeste Aluminiumlegierung EN AW-2618A in verschiedenen Alterungszuständen experimentell charakterisiert und darauf aufbauend Modelle für die Lebensdauerbewertung mit der Finite-Elemente- Methode implementiert.
Materials subjected to high-temperature service conditions will change their microstructure with time. Associated with this aging process is a change of mechanical properties as well as a change of damage mechanisms. Within the scope of the FVV project Aging and Lifetime, Fraunhofer IWM in Freiburg and BAM in Berlin (both Germany) experimentally characterized the widespread high-temperature aluminum alloy EN AW-2618A in different overaging states. Based on the experimental findings, models for numerical lifetime assessment with the finite-element method were implemented.
Wood treated with nano metal fluorides is found to resist fungal decay. Sol−gel synthesis was used to synthesize MgF2 and CaF2 nanoparticles. Electron microscopy images confirmed the localization of MgF2 and CaF2 nanoparticles in wood. Efficacy of nano metal fluoride-treated wood was tested against brown-rot fungi Coniophora puteana and Rhodonia placenta. Untreated wood specimens had higher
mass losses (∼30%) compared to treated specimens, which had average mass loss of 2% against C. puteana and 14% against R. placenta, respectively. Nano metal fluorides provide a viable alternative to current wood preservatives.
The residual stress distribution in IN718 elongated prisms produced by Selective Laser Melting was studied by means of neutron (bulk) and laboratory X-ray (surface) diffraction.
Two deposition hatch lengths were considered. A horizontal plane near the top surface (perpendicular to the building direction) and a vertical plane near the lateral surface (parallel to the building direction) were investigated. Samples both in as-built (AB) condition and removed (RE) from the base plate were characterized.
While surface stress fields seem constant for AB condition, X-ray diffraction shows stress gradients along the hatch direction in the RE condition. The stress profiles correlate with the distortion maps obtained by tactile probe measurements.
Neutron diffraction shows bulk stress gradients for all principal components along the main sample directions. We correlate the observed stress patterns with the hatch length, i.e. with its effect on temperature gradients and heat flow. The bulk stress gradients partially disappear after removal from the baseplate.
Insights into early damage mechanisms during high-temperature gas corrosion provide important aspects for the prediction of the long-term stability of hightemperature materials exposed to a hot and corrosive environment. The current work presents a real time study concerning the combined oxidation and sulfidation of ferritic model alloys in a hot SO2 containing atmosphere using energy dispersive X-ray diffraction. The applied high temperature reactor allows the transmittance of high energetic X-rays in order to collect X-ray diffraction pattern of the sample surface in situ during the reaction with the reactive environment. The results revealed that the first phases crystallizing on iron with 2 wt% chromium and with 9 wt% chromium are oxides. The aging experiments at T = 650° C with 0.5% SO2 and 99.5% Ar were followed in situ and caused an external mixed oxide-sulfide layer on top of iron with 2 wt% chromium. On the higher alloyed material the external scale consists of iron oxides and the inner scale of mixed (Fe,Cr)-oxides and chromium-sulfides. The oxide content continuously increases parallel to an increase of the sulfide amount. Thus, the initially formed (Fe,Cr)-oxides do not have a protective character and support the transport of sulfur through the growing oxide scale.
This study examines the relationship between the magnetic mesostructure with the microstructure of low carbon steel tungsten inert gas welds. Optical microscopy revealed variation in the microstructure of the parent material, in the heat affected and fusion zones, correlating with distinctive changes in the local magnetic stray fields measured with high spatial resolution giant magneto resistance sensors. In the vicinity of the heat affected zone high residual stresses were found using neutron diffraction.
Notably, the gradients of von Mises stress and triaxial magnetic stray field modulus follow the same tendency transverse to the weld. In contrast, micro-X-ray fluorescence characterization indicated that local changes in element composition had no independent effect on magnetic stray fields.