Filtern
Dokumenttyp
- Zeitschriftenartikel (25)
Sprache
- Englisch (25)
Referierte Publikation
- ja (25) (entfernen)
Schlagworte
- Creep (5)
- Microstructure (5)
- Aging (4)
- Additive Manufacturing (3)
- AGIL (2)
- AISI 316L (2)
- Additive manufacturing (2)
- Aluminum alloys (2)
- Electron microscopy (2)
- Fatigue (2)
- Ostwald ripening (2)
- P92 (2)
- Phase-field simulation (2)
- Precipitation (2)
- Residual stress (2)
- S-Phase (2)
- Stress relaxation (2)
- Tempered martensite-ferritic steel (2)
- Ti-6Al-4V (2)
- 316L (1)
- 9-12%Cr steel (1)
- Al-Cu alloy (1)
- Al-Cu-Li-alloy (1)
- Aluminum alloy (1)
- Automated image analysis (1)
- Bitter technique (1)
- Brinell hardness (1)
- Characterisation (1)
- Chemo-mechanical coupling (1)
- Computed Tomography (1)
- Creep behavior (1)
- Creep-fatigue (1)
- Creep-fatigue interaction (1)
- Crystal plasticity (1)
- Cyclic softening (1)
- Damage (1)
- Data Interoperability (1)
- Data infrastructures (1)
- Data mapping (1)
- Deformation (1)
- Differential scanning calorimetry (DSC) (1)
- Digital image correlation (1)
- Digital representations (1)
- Digital workflows (1)
- Domain Ontology Development (1)
- Dwell periods (1)
- Dwell times (1)
- EN AW-2618A (1)
- Elastic modulus (1)
- Elasticity (1)
- Environment (1)
- Expanding cavity model (1)
- FAIR (1)
- FAIR Data Management (1)
- FAIR research data management (1)
- Fatigue damage (1)
- Ferritic–martensitic steel (1)
- General Computer Science (1)
- General Engineering (1)
- General Materials Science (1)
- Heat treatment (1)
- IN 718 (1)
- In-situ Process Monitoring (1)
- Inconel 718 (1)
- Indentation (1)
- Industrial and Manufacturing Engineering (1)
- Interfacial anisotropy (1)
- Knowledge Representation (1)
- Knowledge graphs (1)
- Laser Powder Bed Fusion (1)
- Laser Powder Bed Fusion (LPBF) (1)
- Laser beam melting (LBM) (1)
- Laser powder bed fusion (1)
- Laser powder-based directed energy deposition (1)
- Long-term aging (1)
- Low cycle fatigue (1)
- Low strain (1)
- Low-cycle fatigue (1)
- Magnetic domain distribution (1)
- Magnetic stray fields (1)
- Magnetomechanical effect (1)
- Materials Testing (1)
- Materials informatics (1)
- Mechanical anisotropy (1)
- Metal magnetic memory (1)
- Microstructure evolution (1)
- Misfitting precipitate (1)
- Multiaxial deformation (1)
- Nickel-base alloy (1)
- Non-destructive Materials (1)
- Notch (1)
- Number density (1)
- Ontologies (1)
- Ontology (1)
- PBF-LB/M/316L (1)
- Parametric modeling (1)
- Plastic deformation (1)
- Precipitate shape (1)
- Process development (1)
- Reference data (1)
- Reheating (1)
- Relaxation fatigue (1)
- Reproducibility (1)
- S-phase (1)
- Safety (1)
- Selective laser melting (SLM) (1)
- Semantic Web Technologies (1)
- Shear modulus (1)
- Standardisation (1)
- Strain difference (1)
- Structural steel (1)
- Symmetric dwell periods (1)
- T1 precipitate (1)
- Temperature dependence (1)
- Tensile Test Ontology (1)
- Tensile properties (1)
- Tensile strength (1)
- Thermomechanical fatigue (1)
- Thickening (1)
- Topography (1)
- Transmission electron microscopy (TEM) (1)
- Visual ontology development (1)
- Vocabulary providers (1)
- Volume fraction (1)
- Young's modulus (1)
- microstructural changes (1)
- γ″ phase (1)
- θ′ phase (1)
- θ′-(Al2Cu) precipitate phase (1)
Organisationseinheit der BAM
- 5 Werkstofftechnik (25) (entfernen)
In recent years, the design and development of materials are strongly interconnected with the development of digital technologies. In this respect, efficient data management is the building block of material digitization and, in the field of materials science and engineering (MSE), effective solutions for data standardization and sharing of different digital resources are needed. Therefore, ontologies are applied that represent a map of MSE concepts and relationships between them. Among different ontology development approaches, graphical editing based on standard conceptual modeling languages is increasingly used due to its intuitiveness and simplicity. This approach is also adopted by the Materials-open-Laboratory project (Mat-o-Lab), which aims to develop domain ontologies and method graphs in accordance with testing standards in the field of MSE. To suit the actual demands of domain experts in the project, Ontopanel was created as a plugin for the popular open-source graphical editor diagrams.net to enable graphical ontology editing. It includes a set of pipeline tools to foster ontology development in diagrams.net, comprising imports and reusage of ontologies, converting diagrams to Web Ontology Language (OWL), verifying diagrams using OWL rules, and mapping data. It reduces learning costs by eliminating the need for domain experts to switch between various tools. Brinell hardness testing is chosen in this study as a use case to demonstrate the utilization of Ontopanel.
Creep-fatigue of P92 in service-like tests with combined stress- and strain-controlled dwell times
(2023)
Complex service-like relaxation- and creep-fatigue tests with strain- and stress-controlled dwells and fatigue cycle durations of approx. 2200 s were performed exemplarily on a grade P92 steel at 620 ◦C in this study. The results indicate deviations in the prevailing creep mechanisms of long-term relaxation and creep dwells, affecting subsequent dwells, load shifts, and the macroscopic softening behavior quite differently. In addition, fracture surfaces and longitudinal metallographic sections reveal intergranular crack growth for complex loading with stress-controlled dwells, whereas complex strain-controlled tests enhance oxidation and transgranular crack propagation. These findings substantiate the limited transferability of relaxation-fatigue to creep-fatigue conditions.
The article covers data on the Brinell hardness of the forged precipitation-hardened aluminum alloy EN AW-2618A in the initial T61 condition (i. e. slightly underaged) and after isothermal aging for up to 25,0 0 0 h at aging temperatures between 160 °C and 350 °C. In addition, the hardness was determined on specimens after creep testing at 190 °C and various stresses. The hardness decreases with increasing ag- ing time due to the microstructural evolution of the harden- ing precipitates. The drop occurs faster the higher the aging temperature. Aging under creep load additionally accelerates the hardness decrease.
A study was made on the effect of creep loading on the precipitate radii evolution of the aluminum alloy 2618A.
The overageing process of the alloy was investigated under load at a temperature of 190 °C with stresses between 79 and 181 MPa and compared to stress free isothermal ageing. The precipitates responsible for strength were characterized using dark-field transmission electron microscopy (DFTEM). This allows the experimental Determination of radii distributions of the rod-shaped Al2CuMg precipitates and the evaluation regarding their mean precipitate radius. It was found that the mean precipitate radius enables the comparison of the different microstructural conditions of crept and uncrept samples. The mean precipitate radii of the samples experiencing creep are significantly higher than those of undeformed samples. It was shown that the acquired radii distributions are viable to determine averaged particle radii for comparison of the aged samples. A ripening process including pipe diffusion along dislocations describes the data on coarsening very well for the creep samples.
Results of an extended TMF test program on grade P92 steel in the temperature range of 620 °C - 300 °C, comprising in-phase (IP) and out-of-phase (OP) tests, partly performed with symmetric dwells at Tmax/Tmin, are presented. In contrast to previous studies, the low-strain regime is also illuminated, which approaches flexible operation in a power plant with start/stop cycles. At all strain amplitudes, the material performance is characterized by continuous cyclic softening, which is retarded in tests at lower strains but reaches similar magnitudes in the course of testing. In the investigated temperature range, the phase angle does not affect fatigue life in continuous experiments, whereas the IP condition is more detrimental in tests with dwells. Fractographic analyses indicate creep-dominated and fatigue-dominated damage for IP and OP, respectively. Analyses of the (micro)hardness distribution in the tested specimens suggest an enhanced microstructural softening in tests with dwell times for the low- but not for the high-strain regime. To rationalize the obtained fatigue data, the fracture-mechanics-based D_TMF concept, which was developed for TMF life assessment of ductile alloys, was applied. It is found that the D_TMF parameter correlates well with the measured fatigue lives, suggesting that subcritical growth of cracks (with sizes from a few microns to a few millimeters) governs failure in the investigated range of strain amplitudes.
Abstract While classically used to visualise the magnetic microstructure of functional materials (e.g., for magnetic applications), in this study, the Bitter technique was applied for the first time to visualise macroscopic deformation gradients in a polycrystalline low-carbon steel. Spherical indentation was chosen to produce a multiaxial elastic–plastic deformation state. After removing the residual imprint, the Bitter technique was applied, and macroscopic contrast differences were captured in optical microscopy. To verify this novel characterisation technique, characteristic “hemispherical” deformation zones evolving during indentation were identified using an analytical model from the field of contact mechanics. In addition, near-surface residual stresses were determined experimentally using synchrotron radiation diffraction. It is established that the magnetic domain distribution contrast provides deformation-related information: regions of different domain wall densities correspond to different “hemispherical” deformation zones (i.e., to hydrostatic core, plastic zone and elastic zone, respectively). Moreover, the transitions between these three zones correlate with characteristic features of the residual stress profiles (sign changes in the radial and local extrema in the hoop stress). These results indicate the potential of magnetic domain distribution imaging: visualising macroscopic deformation gradients in fine-grained ferromagnetic material with a significantly improved spatial resolution as compared to integral, mean value-based measurement methods.
Due to their excellent creep resistance and good oxidation resistance, 9–12% Cr ferritic–martensitic stainless steels are widely used as high temperature construction materials in power plants. However, the mutual combination of different loadings (e.g., creep and fatigue), due to a “flexible” operation of power plants, may seriously reduce the lifetimes of the respective components. In the present study, low cycle fatigue (LCF) and relaxation fatigue (RF) tests performed on grade P92 helped to understand the behavior of ferritic–martensitic steels under a combined loading. The softening and lifetime behavior strongly depend on the temperature and total strain range. Especially at small strain amplitudes, the lifetime is seriously reduced when adding a hold time which indicates the importance of considering technically relevant small strains.
It is widely accepted that the magnetic state of a ferromagnetic material may be irreversibly altered by mechanical loading due to magnetoelastic effects. A novel standardized nondestructive testing (NDT) technique uses weak magnetic stray fields, which are assumed to arise from inhomogeneous deformation, for structural health monitoring (i.e., for detection and assessment of damage). However, the mechanical and microstructural complexity of damage has hitherto only been insufficiently considered. The aim of this study is to discuss the phenomenon of inhomogeneous “self-magnetization” of a polycrystalline ferromagnetic material under inhomogeneous deformation experimentally and with stronger material-mechanical focus. To this end, notched specimens were elastically and plastically deformed. Surface magnetic states were measured by a three-axis giant magnetoresistant (GMR) sensor and were compared with strain field (digital image correlation) and optical topography measurements. It is demonstrated that the stray fields do not solely form due to magnetoelastic effects. Instead, inhomogeneous plastic deformation causes topography, which is one of the main origins for the magnetic stray field formation. Additionally, if not considered, topography may falsify the magnetic signals due to variable lift-off values. The correlation of magnetic vector components with mechanical tensors, particularly for multiaxial stress/strain states and inhomogeneous elastic-plastic deformations remains an issue.
Characterization of Ti-6Al-4V fabricated by multilayer laser powder-based directed energy deposition
(2022)
Laser powder-based directed energy deposition (DED-L) is increasingly being used in additive manufacturing (AM). As AM technology, DED-L must consider specific challenges. It must achieve uniform volume growth over hundreds of layers and avoid heat buildup of the deposited material. Herein, Ti–6Al–4V is fabricated using an approach that addresses these challenges and is relevant in terms of transferability to DED–L applications in AM. The assessment of the obtained properties and the discussion of their relationship to the process conditions and resulting microstructure are presented. The quality of the manufacturing process is proven in terms of the reproducibility of properties between individual blanks and with respect to the building height. The characterization demonstrates that excellent mechanical properties are achieved at room temperature and at 400 °C.
Creep and creep damage behavior of stainless steel 316L manufactured by laser powder bed fusion
(2022)
This study presents a thorough characterization of the creep properties of austenitic stainless steel 316L produced by laser powder bed fusion (LPBF 316L) contributing to the sparse available data to date. Experimental results (mechanical tests, microscopy, X-ray computed tomography) concerning the creep deformation and damage mechanisms are presented and discussed. The tested LPBF material exhibits a low defect population, which allows for the isolation and improved understanding of the effect of other typical aspects of an LPBF microstructure on the creep behavior. As a benchmark to assess the material properties of the LPBF 316L, a conventionally manufactured variant of 316L was also tested. To characterize the creep properties, hot tensile tests and constant force creep tests at 600 °C and 650 °C are performed. The creep stress exponents of the LPBF material are smaller than that of the conventional variant. The primary and secondary creep stages and the times to rupture of the LPBF material are shorter than the hot rolled 316L. Overall the creep damage is more extensive in the LPBF material. The creep damage of the LPBF material is overall mainly intergranular. It is presumably caused and accelerated by both the appearance of precipitates at the grain boundaries and the unfavorable orientation of the grain boundaries. Neither the melt pool boundaries nor entrapped gas pores show a significant influence on the creep damage mechanism.