5 Werkstofftechnik
Filtern
Dokumenttyp
Sprache
- Englisch (37) (entfernen)
Referierte Publikation
- ja (37) (entfernen)
Schlagworte
- Additive manufacturing (12)
- Residual stress (9)
- Additive Manufacturing (5)
- Laser powder bed fusion (4)
- Microstructure (4)
- AISI 304L (3)
- AISI 316L (3)
- Hydrogen (3)
- Neutron diffraction (3)
- ToF-SIMS (3)
- AGIL (2)
- Computed Tomography (2)
- Deuterium (2)
- Fatigue (2)
- IN718 (2)
- Inconel 718 (2)
- LPBF (2)
- Laser Powder Bed Fusion (2)
- Microstructure and texture (2)
- Oxidation (2)
- Selective laser melting (2)
- Thermography (2)
- Ti-6Al-4V (2)
- 316L (1)
- 3D printing (1)
- 3D-finite element modeling (1)
- Abrasion (1)
- Aging (1)
- Aluminum alloys (1)
- Austenitic stainless steel (1)
- Burst (1)
- Carbon steel (1)
- Cellular substructure (1)
- Characterisation (1)
- Compositionally complex alloy (1)
- Condensed Matter Physics (1)
- Contact fatigue (1)
- Coordinate measurement machine (1)
- Corrosion pits (1)
- Crack arrest (1)
- Creep (1)
- Creep behavior (1)
- Crystal plasticity (1)
- Defects (1)
- Diffraction (1)
- Ductile iron (1)
- EBSD (1)
- Elastic modulus (1)
- Electron backscatter diffraction (1)
- Electron backscattered diffraction (1)
- Electron microscopy (1)
- Environment (1)
- Fatigue crack propagation stages (1)
- Fatigue damage (1)
- Femtosecond laser (1)
- Fracture mechanics (1)
- Friction (1)
- GMR (1)
- GMR sensors (1)
- General Materials Science (1)
- Global stability criterion (1)
- Grade S960QL steel (1)
- Heat accumulation (1)
- Heat treatment (1)
- High Entropy Alloy (1)
- High temperature corrosion (1)
- High-entropy alloy (1)
- IN 718 (1)
- Impact damage (1)
- In-situ Process Monitoring (1)
- In-situ process monitoring (1)
- Inclusion cluster (1)
- Inclusion size (1)
- Inter layer time (1)
- Iron (1)
- Kernel average misorientation (1)
- Laboratory X-ray diffraction (1)
- Laser Powder Bed Fusion (LPBF) (1)
- Laser beam melting (1)
- Laser beam melting (LBM) (1)
- Laser powder-based directed energy deposition (1)
- Low carbon steel (1)
- Low-cycle fatigue (1)
- Magnetic stray field (1)
- Martensite (1)
- Material modeling (1)
- Mechanical Engineering (1)
- Mechanical anisotropy (1)
- Mechanics of Materials (1)
- Medium Entropy Alloys (1)
- Metal Magnetic Memory (1)
- Micro-shrinkages (1)
- Mis-match (1)
- Multiple cracks (1)
- Natural silver wires (1)
- Neutron Diffraction (1)
- Nickel-based superalloys (1)
- Niobium alloying (1)
- Non-destructive Materials (1)
- Non-metallic inclusions (1)
- Online Process Monitoring (1)
- PBF-LB/M/316L (1)
- Parabolic flight (1)
- Plastic deformation (1)
- Pores (1)
- Principal stress (1)
- Process development (1)
- Projekt AGIL - Alterung additiv gefertigter metallischer Materialien und Komponenten (1)
- Properties (1)
- Reference data (1)
- Residual Stress (1)
- Residual Stresses (1)
- Residual stresses (1)
- Review (1)
- S-Phase (1)
- SEM (1)
- SIMS (1)
- SLM (1)
- Safety (1)
- Scan strategies (1)
- Scratches (1)
- Selective Laser Melting (1)
- Selective laser melting (SLM) (1)
- Shear modulus (1)
- Standardisation (1)
- Statistics (1)
- Steel (1)
- Sulphidation (1)
- Support configurations (1)
- Synchrotron X-ray diffraction (1)
- TIG-welding (1)
- Temperature dependence (1)
- Tensile properties (1)
- Tensile strength (1)
- Tensile testing (1)
- Texture (1)
- Titanium (1)
- Turbine disk (1)
- Ultrasonic assited machining (1)
- Viscoplasticity (1)
- Welding (1)
- X-ray Diffraction (1)
- Young's modulus (1)
- arbidic austempered ductile iron (1)
- µ-gravity (1)
Organisationseinheit der BAM
- 9 Komponentensicherheit (37) (entfernen)
Paper des Monats
- ja (1)
This study investigates the room‐ and high‐temperature (650 °C) tensile and low‐cycle‐fatigue behavior of Inconel 718 produced by laser powder bed fusion (PBF‐LB/M) with a four‐step heat treatment and compares the results to the conventional wrought material. The microstructure after heat treatment is characterized on different length scales. Compared to the wrought variant, the elastic and yield properties are comparable at both test temperatures while tensile strength, ductility, and strain hardening capacity are lower. The fatigue life of the PBF‐LB/M variant at room temperature is slightly lower than that of the wrought material, while at 650 °C, it is vice versa. The cyclic stress response for both material variants is characterized by cyclic softening, which is more pronounced at the higher test temperature. High strain amplitudes (≥0.7%) at room temperature and especially a high testing temperature result in the formation of multiple secondary cracks at the transitions of regions comprising predominantly elongated grain morphology and columns of stacked grains with ripple patterns in the PBF‐LB/M material. This observation and pronounced crack branching and deflection indicate that the cracks are controlled by sharp micromechanical gradients and local crystallite clusters.
High energy X-ray synchrotron diffraction is used to investigate the elastic anisotropy of the nickel-based superalloy IN718 produced by laser powder bed fusion (PBF-LB). This material is characterized by a columnar grain morphology with some crystallographic texture. The material is subjected to elastic loading to determine the diffraction elastic constants (DECs). Furthermore, the single-crystal elastic constants (SCEC) are refined from these experiments using different micromechanical models. The results show that each micromechanical model predicts a specific set of SCEC that well describes the elastic anisotropy of PBF-LB/IN718.
Fatigue tests were performed on the forged aluminum alloy EN AW-2618A in the T61 state. Different stress ratios (R = -1, R = 0.1) were selected to study the influence of mean stress on fatigue life. Two overaged states (10 h/230 ◦C, 1000 h/230 ◦C) were also tested to investigate the influence of overaging on fatigue life. Transmission electron microscopy (TEM) was used to characterize the precipitates (S-phase), which are mainly responsible for the strength of the alloy. A fractographic analysis was also performed to determine the failure mode. Overaging reduces the fatigue life compared to the T61 state. The longer the aging time, the lower the fatigue resistance. The reason is the decrease in (yield) strength, which correlates with the radius of the S-phase: the precipitate radius increases by a factor of approximately two for the overaged states compared to the initial state. The analysis of the fracture surfaces showed crack initiation occurs predominantly on the outer surface and is
associated with the primary phases.
This article reports temperature-dependent elastic properties (Young’s modulus, shear modulus) of three alloys measured by the dynamic resonance method. The alloys Ti-6Al-4V, Inconel IN718, and AISI 316 L were each investigated in a variant produced by an additive manufacturing processing route and by a conventional manufacturing processing route. The datasets include information on processing routes and parameters, heat treatments, grain size, specimen dimensions, and weight, as well as Young’s and shear modulus along with their measurement uncertainty. The process routes and methods are described in detail. The datasets were generated in an accredited testing lab, audited as BAM reference data, and are hosted in the open data repository Zenodo. Possible data usages include the verification of the correctness of the test setup via Young’s modulus comparison in low-cycle fatigue (LCF) or thermo-mechanical fatigue (TMF) testing campaigns, the design auf VHCF specimens and the use as input data for simulation purposes.
Although layer-based additive manufacturing methods such as laser powder bed fusion (PBF-LB) offer an immense geometrical freedom in design, they are typically subject to a build-up of internal stress (i.e. thermal stress) during manufacturing. As a consequence, significant residual stress (RS) is retained in the final part as a footprint of these internal stresses. Furthermore, localized melting and solidification inherently induce columnar-type grain growth accompanied by crystallographic texture. Although diffraction-based methods are commonly used to determine the RS distribution in PBF-LB parts, such features pose metrological challenges in their application. In theory, preferred grain orientation invalidates the hypothesis of isotropic material behavior underlying the common methods to determine RS. In this work, more refined methods are employed to determine RS in PBF-LB/M/IN718 prisms, based on crystallographic texture data. In fact, the employment of direction-dependent elastic constants (i.e. stress factors) for the calculation of RS results in insignificant differences from conventional approaches based on the hypothesis of isotropic mechanical properties. It can be concluded that this result is directly linked to the fact that the {311} lattice planes typically used for RS analysis in nickel-based alloys have high multiplicity and less strong texture intensities compared with other lattice planes. It is also found that the length of the laser scan vectors determines the surface RS distribution in prisms prior to their removal from the baseplate. On removal from the baseplate the surface RS considerably relaxes and/or redistributes; a combination of the geometry and the scanning strategy dictates the sub-surface RS distribution.
The damage mechanisms of metallic components produced by process laser powder bed fusion differ significantly from those typically observed in conventionally manufactured variants of the same alloy. This is due to the unique microstructures of additively manufactured materials. Herein, the focus is on the study of the evolution of creep damage in stainless steel 316L specimens produced by laser powder bed fusion. X-ray computed tomography is used to unravel the influence of the process-specific microstructure from the influence of the initial void distribution on creep damage mechanisms. The void distribution of two specimens tested at 600 °C and 650 °C is analyzed before a creep test, after an interruption, and after fracture. The results indicate that the formation of damage is not connected to the initial void distribution. Instead, damage accumulation at grain boundaries resulting from intergranular cracking is observed.
Aero-engine turbine disks are safety-relevant components which are operated under high thermal and mechanical stress conditions. The actual part qualification and certification procedures make use of spin-tests conducted on production-similar disks. While these tests provide, on the one hand, a reliable definition of the critical conditions for real components, on the other hand they represent a relevant cost item for engine manufacturers. The aim of this work is to present two alternative burst speed assessment methods under development based on the Failure Assessment Diagram (FAD) and a global stability criterion, respectively. In the scope of the fracture mechanics assessment, the failure modes hoop-burst and rim-peeling are investigated with semicircular surface cracks modelled at the critical regions on the turbine disk. The comparison of the predicted critical rotational speed shows good agreement between the assessment methods.
The manufacturability of metallic alloys using laser-based additive manufacturing methods such as laser powder bed fusion has substantially improved within the last decade. However, local melting and solidification cause hierarchically structured and crystallographically textured microstructures possessing large residual stress. Such microstructures are not only the origin of mechanical anisotropy but also pose metrological challenges for the diffraction-based residual stress determination. Here we demonstrate the influence of the build orientation and the texture on the microstructure and consequently the mechanical anisotropy of as-built Inconel 718. For this purpose, we manufactured specimens with [001]/[011]-, [001]- and [011]/[111]-type textures along their loading direction. In addition to changes in the Young’s moduli, the differences in the crystallographic textures result in variations of the yield and ultimate tensile strengths. With this in mind, we studied the anisotropy on the micromechanical scale by subjecting the specimens to tensile loads along the different texture directions during in situ neutron diffraction experiments. In this context, the response of multiple lattice planes up to a tensile strain of 10% displayed differences in the load partitioning and the residual strain accumulation for the specimen with [011]/[111]-type texture. However, the relative behavior of the specimens possessing an [001]/[011]- and [001]-type texture remained qualitatively similar. The consequences on the metrology of residual stress determination methods are discussed.
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.