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5 Werkstofftechnik

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Autor

  • Skrotzki, Birgit (65)
  • Nolze, Gert (64)
  • Günster, Jens (59)
  • Kranzmann, Axel (52)
  • Trappe, Volker (51)
  • Braun, Ulrike (47)
  • Müller, Ralf (47)
  • Rockenhäuser, Christian (40)
  • Bettge, Dirk (36)
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  • Corrosion (50)
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Organisationseinheit der BAM

  • 5 Werkstofftechnik (1207)
  • 5.1 Materialographie, Fraktographie und Alterung technischer Werkstoffe (335)
  • 5.2 Experimentelle und modellbasierte Werkstoffmechanik (247)
  • 5.3 Mechanik der Polymerwerkstoffe (217)
  • 5.6 Glas (166)
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  • 7 Bauwerkssicherheit (103)
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On the long-term aging of S-phase in aluminum alloy 2618A (2021)
Rockenhäuser, Christian ; Rowolt, C. ; Milkereit, B. ; Darvishi Kamachali, Reza ; Kessler, O. ; Skrotzki, Birgit
The aluminum alloy 2618A is applied for engine components such as radial compressor wheels which operate for long time at elevated temperatures. This results in coarsening of the hardening precipitates and degradation in mechanical properties during the long-term operation, which is not taken into account in the current lifetime prediction models due to the lack of quantitative microstructural and mechanical data. To address this issue, a quantitative investigation on the evolution of precipitates during long-term aging at 190 °C for up to 25,000 h was conducted. Detailed transmission electron microscopy (TEM) was combined with Brinell hardness measurements and thorough differential scanning calorimetry (DSC) experiments. The results showthat GPB zones and S-phase Al2CuMg grow up to < 1,000 h during which the GPB zones dissolve and S-phase precipitates form. For longer aging times, only S-phase precipitates coarsen, which can be well described using the Lifshitz–Slyozov Wagner theory of ripening. A thorough understanding of the underlying microstructural processes is a prerequisite to enable the integration of aging behavior into the established lifetime models for components manufactured from alloy 2618A.
Corrosion Study on Wellbore Materials for the CO2 Injection Process (2021)
Le, Quynh Hoa ; Bäßler, Ralph ; Bettge, Dirk ; Buggisch, E. ; Schiller, Bernadette Nicole ; Beck, M.
For reliability and safety issues of injection wells, corrosion resistance of materials used needs to be determined. Herein, representative low-cost materials, including carbon steel X70/1.8977 and low alloyed steel 1.7225, were embedded in mortar to mimic the realistic casing-mortar interface. Two types of cement were investigated: (1) Dyckerhoff Variodur commercial Portland cement, representing a highly acidic resistant cement and (2) Wollastonite, which can react with CO2 and become stable under a CO2 stream due to the carbonation process. Exposure tests were performed under 10 MPa and at 333 K in artificial aquifer fluid for up to 20 weeks, revealing crevice corrosion and uniform corrosion instead of expected pitting corrosion. To clarify the role of cement, simulated pore water was made by dispersing cement powder in aquifer fluid and used as a solution to expose steels. Surface analysis, accompanied by element mapping on exposed specimens and their crosssections, was carried out to trace the chloride intrusion and corrosion process that followed.
Fractographic Analysis of Fatigue Striations Formation under different Microstructures and Loading Conditions (2020)
Duarte, Larissa ; Andrade, Ana Carolina ; Bettge, Dirk
Fatigue failure of a component can occur at service loads considerably lower than the yield strength of the material. Under fatigue loading condition, the material in the vicinity of the tip of a propagating crack repeatedly deforms plastically, leaving microscopic marks on the crack surface, commonly known as fatigue striations. Counting and measuring fatigue striations is a method in estimating the number of loading cycles a component went through until fracture. Some studies suggest a one-to-one relation between the number of fatigue striations and the number of load cycles, but this relation is still debatable, given that there are many factors influencing the formation of those striations. The main purpose of this work is to analyze the influence of microstructure and mechanical strength on the formation of fatigue striations in structural steels, in order to understand how these material properties are related to the fatigue crack behavior. For such, standard Charpy-V samples were subjected to hardness, fatigue and impact testing. Metallography was performed to characterize the microstructure, and a fractographic analysis by using optical and scanning electron microscopy was carried out to investigate the fracture surface. This study shows that steels with higher ductility have a closer one-to-one relation than those with a higher tensile strength. Above a certain level of tensile strength, fatigue striations do form rarely or completely disappear.
Segregation-assisted spinodal and transient spinodal phase separation at grain boundaries (2020)
Darvishi Kamachali, Reza ; da Silva, A. ; McEniry, E. ; Gault, B. ; Neugebauer, J. ; Raabe, D.
Segregation to grain boundaries affects their cohesion, corrosion, and embrittlement and plays a critical role in heterogeneous nucleation. In order to quantitatively study segregation and low-dimensional phase separation at grain boundaries, here, we apply a density-based phase-field model. The current model describes the grain-boundary thermodynamic properties based on available bulk thermodynamic data, while the grain-boundary-density profile is obtained using atomistic simulations. To benchmark the performance of the model, Mn grain-boundary segregation in the Fe–Mn system is studied. 3D simulation results are compared against atom probe tomography measurements conducted for three alloy compositions. We show that a continuous increase in the alloy composition results in a discontinuous jump in the segregation isotherm. The jump corresponds to a spinodal Phase separation at grain boundary. For alloy compositions above the jump, we reveal an interfacial transient spinodal phase separation. The transient spinodal phenomenon opens opportunities for knowledge-based microstructure design through the chemical manipulation of grain boundaries. The proposed density-based model provides a powerful tool to study thermodynamics and kinetics of segregation and phase changes at grain boundaries.
Critical role of scan strategies on the development of microstructure, texture, and residual stresses during laser powder bed fusion additive manufacturing (2021)
Nadammal, Naresh ; Mishurova, Tatiana ; Fritsch, Tobias ; Serrano-Munoz, Itziar ; Kromm, Arne ; Haberland, C. ; Portella, Pedro Dollabella ; Bruno, Giovanni
Laser based powder bed fusion additive manufacturing offers the flexibility to incorporate standard and userdefined scan strategies in a layer or in between the layers for the customized fabrication of metallic components. In the present study, four different scan strategies and their impact on the development of microstructure, texture, and residual stresses in laser powder bed fusion additive manufacturing of a nickel-based superalloy Inconel 718 was investigated. Light microscopy, scanning electron microscopy combined with electron backscatter diffraction, and neutron diffraction were used as the characterization tools. Strong textures with epitaxially grown columnar grains were observed along the build direction for the two individual scan strategies. Patterns depicting the respective scan strategies were visible in the build plane, which dictated the microstructure development in the other planes. An alternating strategy combining the individual strategies in the successive layers and a 67◦ rotational strategy weakened the texture by forming finer microstructural features. Von Mises equivalent stress plots revealed lower stress values and gradients, which translates as lower distortions for the alternating and rotational strategies. Overall results confirmed the scope for manipulating the microstructure, texture, and residual stresses during laser powder bed fusion additive manufacturing by effectively controlling the scan strategies.
Mechanical anisotropy of additively manufactured stainless steel 316l: an experimental and numerical study (2020)
Charmi, Amir
This work aims for a yield function description of additively manufactured (AM) parts of stainless steel 316L at the continuum-mechanical macro-scale by means of so-called virtual experiments using a crystal plasticity model at meso-scale.
Development and characterization of starch film and the incorporation of silver nanoparticles (2020)
Cornelsen Sampaio Kling, I. ; Pauw, Brian R. ; Jacome, Leonardo A. ; Archanjo, B. S. ; Simão, R. A.
Starch is one of the biopolymers being used for bioplastic synthesis. For production, starch can be combined with different plasticizers, starches from different plant sources and even with nanomaterials to improve or to add film properties. The challenge of adding these, e.g. in the form of silver nanoparticles (AgNp) is to determine the concentration so as to avoid impairing the properties of the film, agglomeration or altering the visual characteristics of the film. In this study, a starch film synthesis route and the incorporation of silver nanoparticles has been proposed in order not to alter the properties of the film while maintaining the transparency and a clear colour of the starch film. The results showed that the proposed synthesis route is promising, efficient, reproducible, fast and the film has good mechanical properties.
Mechanical behaviour of AM metals: Creep of LPBF 316L and low-cycle-fatigue of LMD Ti-6Al-4V (2020)
Ávila Calderón, Luis Alexander
Additively manufactured metallic materials have already started to find application in safety-relevant components. However, this has only happened for certain materials and specific applications and loading conditions, since there is still an extensive lack of knowledge as well as of historical data regarding their mechanical behaviour. This contribution aims to address this lack of understanding and historical data concerning the creep behaviour of the austenitic stainless steel 316L manufactured by Laser-Powder-Bed-Fusion (L-PBF) and the low-cycle-fatigue behaviour of the titanium alloy Ti-6Al-4V manufactured by Laser-Metal-Deposition (LMD). Furthermore, it aims to assess their mechanical behaviour against their conventional counterparts. With that in mind, specimens from conventional and additive materials are tested and their mechanical behaviour analysed based on characteristic curves. To understand the damage behaviours the materials are characterized by destructive and non-destructive techniques before and after failure.
Composite materials - focus polymer matrix composites (PMC) (2020)
Trappe, Volker
Lecture about polymer matrix composites as part of the first trainings event GW4SHM, properties, production, basic theory, testing.
EBSD Kikuchi Pattern Analysis, Silicon 15kV (2019)
Winkelmann, A. ; Britton, T. B. ; Nolze, Gert
Supplementary data and images for Si EBSD pattern analysis as presented in: A. Winkelmann, T.B. Britton, G. Nolze "Constraints on the effective electron energy spectrum in backscatter Kikuchi diffraction", Physical Review B (2019).
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