5 Werkstofftechnik
Filtern
Dokumenttyp
- Vortrag (121)
- Zeitschriftenartikel (71)
- Beitrag zu einem Tagungsband (24)
- Forschungsdatensatz (21)
- Posterpräsentation (20)
- Buchkapitel (7)
- Dissertation (4)
- Forschungsbericht (4)
- Sammelband (Herausgeberschaft für den kompletten Band) (3)
- Monografie (1)
Sprache
- Englisch (227)
- Deutsch (49)
- Französisch (1)
Schlagworte
- Ontology (33)
- Creep (27)
- Microstructure (23)
- Additive manufacturing (21)
- LCF (16)
- Additive Manufacturing (14)
- Degradation (13)
- Fatigue (13)
- Ti-6Al-4V (13)
- Aluminium (11)
- Alloy 2618A (10)
- Coarsening (10)
- FAIR (10)
- 316L (9)
- Aging (9)
- EN AW-2618A (9)
- Low Cycle Fatigue (9)
- Transmission electron microscopy (9)
- Crystal plasticity (8)
- Digitalization (8)
- Nickel-base superalloys (8)
- Ontologie (8)
- Residual stress (8)
- S-phase (8)
- Semantic Web Technologies (8)
- AGIL (7)
- AISI 316L (7)
- Additive Fertigung (7)
- Aluminium alloy (7)
- Anisotropy (7)
- Kriechen (7)
- Mechanical testing (7)
- Plattform MaterialDigital (7)
- Semantic Interoperability (7)
- Thermomechanical fatigue (7)
- Zugversuch (7)
- Data Interoperability (6)
- Knowledge Representation (6)
- Mikrostruktur (6)
- P92 (6)
- TMF (6)
- Computed Tomography (5)
- Crack growth (5)
- Damage (5)
- Dark-field transmission electron microscopy (DFTEM) (5)
- Data mapping (5)
- Digitalisierung (5)
- FAIR data (5)
- FAIR data management (5)
- Fe-Al alloys (5)
- HIP (5)
- Intermetallics (5)
- Iron aluminides (5)
- Knowledge graph and ontologies (5)
- Laser powder bed fusion (5)
- PMD Core Ontology (5)
- Reference data (5)
- Shear modulus (5)
- Stress relaxation (5)
- Tensile Test (5)
- Tensile testing (5)
- Wissensrepräsentation (5)
- Young's modulus (5)
- Aluminum alloys (4)
- Brinell hardness (4)
- Creep-fatigue (4)
- Data Fusion (4)
- EBSD (4)
- Elastic modulus (4)
- Electron microscopy (4)
- Fatigue crack growth (4)
- Laser Powder Bed Fusion (4)
- Microstrucrue Design (4)
- Ni-Resist (4)
- Normung (4)
- Phase-field simulation (4)
- Plattform Material Digital (4)
- Scale-bridging (4)
- Schädigung (4)
- Superalloy (4)
- Tensile Test Ontology (4)
- Tensile test (4)
- Virtual experiments (4)
- Crack (3)
- Crack propagation (3)
- Crack tip opening displacement (3)
- Creep behavior (3)
- Creep data (3)
- Dark-field transmission electron microscopy (3)
- Diffraction (3)
- Digtial Representation (3)
- Electronic Lab Notebook (3)
- Ferritic-martensitic steels (3)
- Fractography (3)
- Hardness (3)
- Heat treatment (3)
- High temperature mechanical properties (3)
- IN 718 (3)
- Interoperability (3)
- Knowledge graph (3)
- Lebensdauer (3)
- Low cycle fatigue (3)
- Mechanical behavior (3)
- Mechanische Eigenschaften (3)
- Metadata schema (3)
- Microstructure evolution (3)
- Ontologies (3)
- PBF-LB/M/316L (3)
- PMDco (3)
- Phase-field (3)
- Precipitation (3)
- Referenzdaten (3)
- Reproducibility (3)
- Research Data Management (3)
- S-Phase (3)
- Semantic Data (3)
- Semantic Web (3)
- Single-crystals (3)
- Superalloys (3)
- Superlegierung (3)
- Syngle Crystal alloy (3)
- Tempered Martensite Ferritic Steels (3)
- Tempered martensite-ferritic steel (3)
- Tensile data (3)
- Thermo-Mechanical Fatigue (3)
- Al-Cu-Li alloys (2)
- Alterung (2)
- Aluminium Alloy (2)
- Aluminum (2)
- Aluminum alloy (2)
- CALPHAD (2)
- CT (2)
- Casting (2)
- Chemo-mechanical coupling (2)
- Computed tomography (2)
- Concrete (2)
- Continnum damage model (2)
- Copper (2)
- Copper alloys (2)
- Creep-Fatigue (2)
- Cyclic softening (2)
- Data Management (2)
- Data Structures (2)
- Data management (2)
- Dataset (2)
- Density-based Thermodynamics (2)
- Density-based model (2)
- Densty-based Thermodynamics (2)
- Diffraction Elastic Constants (2)
- Diffusion (2)
- Digital material representation (2)
- Digital representation (2)
- Digitization (2)
- Dislocation (2)
- Dislocations (2)
- Elasticity (2)
- Electron Backscatter Diffraction (2)
- Electron backscatter diffraction (2)
- Environmentally assisted cracking (2)
- FAIR Data Management (2)
- Fatigue performance (2)
- Fatigue testing (2)
- Finite element analysis (2)
- Fracture mechanics (2)
- Glass forming (2)
- High Cycle Fatigue (2)
- High Temperature Testing (2)
- Joined nickel-based alloys (2)
- Kleinprobenprüfung (2)
- Knowledge Graph (2)
- Laser Powder Bed fusion (2)
- Long-term behavior (2)
- Mass transport (2)
- Material digital (2)
- Materials science (2)
- Metal seal (2)
- Micromechanical model (2)
- Microstructure-property-correlation (2)
- Multiaxial deformation (2)
- NFDI (2)
- Neutron diffraction (2)
- Nickel-base alloy (2)
- Notches (2)
- Ontologien (2)
- Ontology development (2)
- Ostwald ripening (2)
- PMD (2)
- Parametric modeling (2)
- Plastic deformation (2)
- Polymer (2)
- Probengrößeneffekt (2)
- Rapid solidification (2)
- Residual Stress (2)
- S355 steel sheet (2)
- Semantic Representation (2)
- Semantic web (2)
- Semantisches Web (2)
- Simulation (2)
- Simulation of concrete (2)
- Single-Crystal (2)
- Standard (2)
- Standardisierung (2)
- Standardization (2)
- Structural steel (2)
- Superconducting magnet (2)
- Symmetric dwell periods (2)
- TEM (2)
- Tensile Properties (2)
- Thermodynamics (2)
- Ti64 (2)
- TiAl5V4 (2)
- Titan (2)
- Titanium (2)
- Under cyclic loading (2)
- Vickers hardness (2)
- Viscoplasticity (2)
- Wall thickness (2)
- Zugeigenschaften (2)
- 316L stainless steel (1)
- 3D-finite element modeling (1)
- 9-12% Cr ferritic-martensitic steels (1)
- 9-12%Cr steel (1)
- 9–12%Cr steel (1)
- AM (1)
- Abgasturbolader Heißteile (1)
- Accelerated integration scheme (1)
- Accelerated temporal integration (1)
- Accessible (1)
- Age hardening (1)
- Ageing (1)
- Al alloys (1)
- Al-Cu alloy (1)
- Al-Cu-Li-alloy (1)
- Al-Li alloys (1)
- Al2CuMg (1)
- Allgemeine Grundlagen (1)
- Alloy 2818A (1)
- Alloy design (1)
- Alloy microstructure (1)
- Aluminiumlegierung (1)
- Aluminum Alloy Aging (1)
- Anwendungen (1)
- Atomistic simulations (1)
- Aufbau von Festkörpern (1)
- Austenite-to-martensite phase transformation (1)
- Austenitic cast iron (1)
- Austenitischer Stahl (1)
- Automatable digital approach (1)
- Automated finite element analysis (1)
- Automated image analysis (1)
- Automation (1)
- Automatische Finite Element Simulation (1)
- Beanspruchung (1)
- Bitter technique (1)
- Bruch (1)
- CKAN (1)
- CMSX4 (1)
- Calibration (1)
- Carbon steel (1)
- Centrifugal casting (1)
- Centrifugal compressor wheel (1)
- Characterisation (1)
- Characterization (1)
- Charpy test (1)
- Chemische Analyse (1)
- Coefficient of thermal expansion (1)
- Complex borides (1)
- Compositionally complex alloys (1)
- Contact mechanics (1)
- Corrosion (1)
- Craze-crack mechanism (1)
- Creep behaviour (1)
- Creep mechanisms (1)
- Creep, Creep Rupture, and Stress Rupture (1)
- Creep-fatigue interaction (1)
- Crystal Defects (1)
- Crystal Plasticity Modelling (1)
- Crystalline defects (1)
- Cyclic loading (1)
- Cyclic oxidation (1)
- DED-L (1)
- DIN (1)
- Damage Behavior (1)
- Damage behavior (1)
- Data Exchange (1)
- Data Integration (1)
- Data Mapping (1)
- Data format (1)
- Data infrastructures (1)
- Data linking (1)
- Data pipeline concept (1)
- Data storage (1)
- Data structure (1)
- Datenfusion (1)
- Datenökosystem (1)
- Defects (1)
- Defects engineering (1)
- Defects phase diagram (1)
- Defects thermodynamics (1)
- Deformation (1)
- Deformation mechanisms (1)
- Demonstrators (1)
- Die casting (1)
- Differential scanning calorimetry (DSC) (1)
- Digital Transformation (1)
- Digital image correlation (1)
- Digital representations (1)
- Digital workflow (1)
- Digital workflows (1)
- Digitalizations (1)
- Domain Ontology Development (1)
- Dwell periods (1)
- Dwell times (1)
- Dwell-Fatigue (1)
- EN AW 2618A (1)
- EN AW 2618A a (1)
- Eigenschaften (1)
- Eigenspannung (1)
- Elastic constants (1)
- Elastic energy (1)
- Elctronic Lab Notebook (1)
- Electrical resistance (1)
- Electrochemical dressing (1)
- Electropolishing (1)
- Elektronisches Laborbuch (ELN) (1)
- Elektrotechnische Grundlagen (1)
- Energiewende (1)
- Energy transition (1)
- Entwicklung (1)
- Environment (1)
- Environmental Stress Cracking (1)
- Environmental stress cracking (ESC) (1)
- Ermüdung (1)
- Expanding cavity model (1)
- FAIR Data (1)
- FAIR data. (1)
- FAIR principles (1)
- FAIR research data management (1)
- FNCT (1)
- Fatigue crack propagation (1)
- Fatigue damage (1)
- Ferritic–martensitic steel (1)
- Finite elmenet simulation (1)
- Finite-Elemente-Methode (1)
- Fourier series (1)
- Full notch creep test (FNCT) (1)
- Full-Notch Creep Test (1)
- Full-notch creep test (1)
- Fullerite (1)
- GMR (1)
- GMR sensors (1)
- Gefügeuntersuchung (1)
- Gefügte Nickelbasislegierungen (1)
- General Chemistry (1)
- General Computer Science (1)
- General Engineering (1)
- General Materials Science (1)
- Glas (1)
- Gleichgewicht (1)
- Grade S960QL steel (1)
- Gradient-enhanced fatigue model (1)
- Grain Boundary Phase Diagram (1)
- Grain Boundary Segregation (1)
- Grain Boundary Spinodal (1)
- Grain boundaries (1)
- Grain boundary (1)
- Grain boundary phase diagram (1)
- Grain boundary thermodynamics (1)
- Graphic design (1)
- Grundlagen des Maschinenbaus (1)
- HCF (1)
- Hardness test (1)
- Heat Treatment (1)
- Hertzian cracks (1)
- High cycle fatigue (1)
- High entropy alloy (1)
- High entropy alloys (1)
- High-Entropy Alloys (1)
- High-entropy alloys (1)
- High-strength steel (1)
- High-temperature corrosion (1)
- Hochentropie-Legierung (1)
- Hochtemperatur (1)
- Hochtemperaturermüdung (1)
- Honing (1)
- Honing Stone (1)
- Hot isostatic pressing (HIP) (1)
- IN718 (1)
- In-Situ Testing (1)
- In-situ Process Monitoring (1)
- In-situ SEM micro shear deformation (1)
- In-situ diffraction (1)
- Inconel 718 (1)
- Incremental lifetime models (1)
- Indentation (1)
- Industrial and Manufacturing Engineering (1)
- Informationstechnische Grundlagen (1)
- Interfacial Spinodal (1)
- Interfacial anisotropy (1)
- Interfacial free energy (1)
- Intermetallische FeAl-Legierungen (1)
- Interoperable (1)
- Inverse ostwald ripening (1)
- Investment casting (1)
- Irregular topography (1)
- Isostatic hot pressing (HIP) (1)
- Kennwertermittlung (1)
- Keramik (1)
- Knowledge Graphs (1)
- Knowledge graphs (1)
- Knowledge representation (1)
- Korrosion (1)
- Kreislaufwirtschaft (1)
- Kriechermüdung (1)
- Kristallsystem (1)
- Kupfer (1)
- L-PBF 316L (1)
- LMD (1)
- Laser Poeder Bed Fusion (1)
- Laser Powder Bed Fusion (LPBF) (1)
- Laser Scanning Microscopy (1)
- Laser beam melting (LBM) (1)
- Laser powder-based directed energy deposition (1)
- Laser scanning microscopy (LSM) (1)
- Laser-Pulverbettschmelzen (1)
- Layering misalignment (1)
- Lebensdauervorhersage (1)
- Legierung mit komplexer Zusammensetzung (1)
- Life cycle (1)
- Lifetime prediction (1)
- Linked open data (1)
- Long-term aging (1)
- Low Cycle Fatigue (LCF) (1)
- Low carbon steel (1)
- Low strain (1)
- Low-Cycle Fatigue (LCF) (1)
- Low-Cycle-Fatigue (1)
- Low-cycle fatigue (1)
- Low-cycle fatigue. (1)
- Low-cycle-fatigue behaviour (1)
- Lötverbindung (1)
- Machine learning (1)
- Magnetic domain distribution (1)
- Magnetic domains (1)
- Magnetic stray field (1)
- Magnetic stray fields (1)
- Magnetische Domänen (1)
- Magnetoelastic effect (1)
- Magnetoelastischer Effekt (1)
- Magnetomechanical effect (1)
- Martensitic transformation (1)
- Mat-o-lab (1)
- Material Life Cycle (1)
- Material degradation (1)
- Material modeling (1)
- MaterialDigital (1)
- Materialcharakterisierung (1)
- Materialentwicklung (1)
- Materialkreislauf (1)
- Materialprüfung (1)
- Materials Chemistry (1)
- Materials Science (1)
- Materials Testing (1)
- Materials and Processes Data Reusability (1)
- Materials informatics (1)
- Materials science and engineering (1)
- Materials testing (1)
- Mathematisch-naturwissenschaftliche Grundlagen (1)
- Mechanical Engineering (1)
- Mechanical Properties (1)
- Mechanical anisotropy (1)
- Mechanics of Materials (1)
- Mechanisches Verhalten (1)
- Mechanistic Modelling (1)
- Mehrachsige Verformung (1)
- Mehrskalenmodell (1)
- Metal Magnetic Memory (1)
- Metal magnetic memory (1)
- Metall (1)
- Metals and Alloys (1)
- Micro computed tomography (1)
- Microstructural evolution (1)
- Microstructure analysis (1)
- Microstructure characterisation (1)
- Microstructure modification (1)
- Mid-Level Ontology for MSE (1)
- Mikro-Computertomographie (1)
- Mikrostrukturentwicklung (1)
- Mikrostrukturuntersuchung (1)
- Miniature specimens (1)
- Misfitting precipitate (1)
- Missing acknowledgment (1)
- Model (1)
- Modeling (1)
- Modell (1)
- Molecular dynamics (1)
- NFDI-MatWerk (1)
- NIST (1)
- Nanocrystalline alloys (1)
- Nanoindentation (1)
- NiTi (1)
- Nickel alloys (1)
- Nickel-base superalloy (1)
- Nimonic 75 (1)
- Non-destructive Materials (1)
- Non-destructive testing (1)
- Notch (1)
- Number density (1)
- Numerische Simulation (1)
- Ordering (1)
- Orowan Mechanism (1)
- Overaging (1)
- P92 steels (1)
- PE-HD (1)
- Phase Diagram (1)
- Phase field crystal (1)
- Phase field method (1)
- Phase field model (1)
- Phase field simulation (1)
- Phase stability (1)
- Phase-field model (1)
- Plasticity (1)
- Platform Material Digital (1)
- Platform Material Digital (PMD) (1)
- Platform MaterialDigital (1)
- Platform MaterialDigital (PMD) (1)
- Plattform Material Digital (PMD) (1)
- Polyethylene (1)
- Pore (1)
- Pores (1)
- Porosity (1)
- Positron annihilation spectroscopy (1)
- Power plant (1)
- Precipitate shape (1)
- Precipitates (1)
- Precipitation Analysis (1)
- Precipitation hardening (1)
- Process development (1)
- Quantitative Precipitation Analysis (1)
- Quantitative image analysis (1)
- Radii distribution (1)
- Rafting (1)
- Reference Data (1)
- Reference Dataset (1)
- Reference material BCR-425 (1)
- Referenzmaterial (1)
- Referenzorganismus (1)
- Referenzverfahren (1)
- Reheating (1)
- Relaxation fatigue (1)
- Relaxation tests (1)
- Resonance testing (1)
- Reusability (1)
- Reusable data (1)
- Rissausbreitung (1)
- Risse (1)
- Rissform (1)
- Rissfortschritt (1)
- Rissverlauf (1)
- SEN-Probe (1)
- Safety (1)
- Schadenskunde (1)
- Selective laser melting (1)
- Selective laser melting (SLM) (1)
- Semantic Data Integration (1)
- Semantic Interioerability (1)
- Semantic Web technologies (1)
- Semantic data integration (1)
- Semantic interoperability (1)
- Semantic structuring (1)
- Semantische Daten (1)
- Shape memory alloy (1)
- Shape memory alloys (1)
- Shear testing (1)
- Simulationsgestützte Gießkonzepte (1)
- Single crystal superalloys (1)
- Single-crystal (1)
- Slow crack growth (SCG) (1)
- Solidification (1)
- Spinodal Decomposition (1)
- Spinodal decomposition (1)
- Standardisation (1)
- Strain difference (1)
- Strain energy (1)
- Strength (1)
- Stress-strain behavior (1)
- Stress-strain-behavior (1)
- Structured Data (1)
- Struktur (1)
- Superalloy single crystals (1)
- T1 precipitate (1)
- TIG-welding (1)
- TMF experiments (1)
- Temperature dependence (1)
- Tempered martensite ferritic steels (1)
- Tensile properties (1)
- Tensile strength (1)
- Tensile stress relaxation (1)
- Tensile stress relaxation testing (1)
- Tensile tests (1)
- Texture (1)
- Thermal Cycling (1)
- Thermal expansion (1)
- Thermo-mechanical fatigue (1)
- Thermographie (1)
- Thermomechanical Fatigue (TMF) (1)
- Thermomechanische Ermüdung (1)
- Thermophysikalische Eigenschaften (1)
- Thesaurus (1)
- Thickening (1)
- Tools (1)
- Topography (1)
- Transmission electron microscopy (TEM) (1)
- Tribologie (1)
- Ungleichgewicht (1)
- Unlegierter Baustahl (1)
- Vacancies (1)
- Verbundwerkstoff (1)
- Vernetzung (1)
- Vickers Hardness (1)
- Virtueller Materialdatenraum (1)
- Viskoplastisch (1)
- Visual ontology development (1)
- Vocabulary providers (1)
- Volume fraction (1)
- Werkstoffauswahl (1)
- Werkstoffkennwerte (1)
- Werkstoffmechanische Prüfung (1)
- Werkstoffprüfung (1)
- Workshop (1)
- X-ray computed tomography (CT) (1)
- Young`s modulus (1)
- Young´s modulus (1)
- Zerstörungsfreie Prüfung (1)
- Zugversuchsontologie (1)
- coarsening (1)
- hardness (1)
- microstructural changes (1)
- γ″ phase (1)
- θ′ phase (1)
- θ′-(Al2Cu) precipitate phase (1)
Organisationseinheit der BAM
- 5.2 Metallische Hochtemperaturwerkstoffe (277) (entfernen)
Paper des Monats
- ja (1)
The studied aluminium alloy is EN AW-2618A (2618A). It is very widely used for exhaust gas turbo-charger compressor wheels. Due to long operating times, high cycle fatigue (HCF) and material aging under the influence of temperatures up to 230 °C is particularly relevant for the wheels. The wheels are typically milled from round wrought blanks. From such round blanks, different testpieces are extracted and a comprehensive series of HCF tests is conducted at room temperature. The tests investigate the materials fatigue performance in the T61 state for two load-ratios, namely R = -1 and R = 0.1. Additionally, two overaged material states are tested, accounting for the aging process the material undergoes during long operating times at high temperatures. The experimental results are evaluated and compared to each other.
Furthermore, the design process of notched specimens is presented. With the notched specimens, it is aimed to quantify the notch sensitivity of the material. Relating thereto, two potential model parameters for the fatigue lifetime model are introduced.
The amount of data generated worldwide is constantly increasing. These data come from a wide variety of sources and systems, are processed differently, have a multitude of formats, and are stored in an untraceable and unstructured manner, predominantly in natural language in data silos. This problem can be equally applied to the heterogeneous research data from materials science and engineering. In this domain, ways and solutions are increasingly being generated to smartly link material data together with their contextual information in a uniform and well-structured manner on platforms, thus making them discoverable, retrievable, and reusable for research and industry. Ontologies play a key role in this context. They enable the sustainable representation of expert knowledge and the semantically structured filling of databases with computer-processable data triples.
In this perspective article, we present the project initiative Materials-open-Laboratory (Mat-o-Lab) that aims to provide a collaborative environment for domain experts to digitize their research results and processes and make them fit for data-driven materials research and development. The overarching challenge is to generate connection points to further link data from other domains to harness the promised potential of big materials data and harvest new knowledge.
The studied aluminium alloy is EN AW-2618A (2618A). It is very widely used for exhaust gas turbo-charger compressor wheels. Due to long operating times, high cycle fatigue (HCF) and material aging under the influence of temperatures up to 230 °C is particularly relevant for the wheels. The wheels are typically milled from round wrought blanks. From such round blanks, different testpieces are extracted and a comprehensive series of HCF tests is conducted at room temperature. The tests investigate the materials fatigue performance in the T61 state for two load-ratios, namely R = -1 and R = 0.1. Additionally, two overaged material states are tested, accounting for the aging process the material undergoes during long operating times at high temperatures. The experimental results are evaluated and compared to each other.
Furthermore, the design process of notched specimens is presented. With the notched specimens, it is aimed to quantify the notch sensitivity of the material. Relating thereto, two potential model parameters for the fatigue lifetime model are introduced. Finally, the extended research data management in this project is highlighted and its advantages for sustainable use in material science and engineering applications are shown.
In this paper, columnar cellular growth with kinetic effects including kinetic undercooling and solute trapping in rapid directional solidification of alloys was investigated by using a recent quantitative phase-field model for rapid solidification. Morphological transition and primary spacing selection with and without kinetic effects were numerically investigated. Numerical results show that doublon structure is an intermediate state in the primary spacing adjustment of cellular arrays. It was found that the inclusions of kinetic effects result in the increase of the solute in the solid phase and the solute enrichment in the interdendritic liquid channel. Moreover, predicted results indicate that the growth directions of the cellular arrays in rapid directional solidification with and without kinetic effects are independent of the Péclet number. Therefore, the kinetic effects play important roles in numerical simulations of the growth pattern selection and solute distribution during rapid solidification. Neglecting them will result in the inaccurately predicted results.
The finite element software ProCrackPlast is developed for the automated simulation of fatigue crack growth in arbitrarily loaded three-dimensional components with large scale plastic deformations, in particular under cyclic thermomechanical (TMF) loading.
ProCrackPlast is developed by extending the software Procrack, created at TU Freiberg for linear-elastic crack growth simulations. The pre-processing, FEM analysis, and the post-processing in ProCrackPlast are done by the commercial software ABAQUS. ProCrackPlast resorts to a crack growth procedure which adaptively updates the crack in finite increments based on the fracture-mechanical parameter, cyclic crack tip opening displacement ΔCTOD . Features of this software along with two application examples of fatigue crack growth in a typical cast steel, Ni-Resist, are presented in this paper to show its capability and performance.
Grain boundaries (GBs) are planar lattice defects that govern the properties of many types of polycrystalline materials. Hence, their structures have been investigated in great detail. However, much less is known about their chemical features, owing to the experimental difficulties to probe these features at the atomic length scale inside bulk material specimens. Atom probe tomography (APT) is a tool capable of accomplishing this task, with an ability to quantify chemical characteristics at near-atomic scale. Using APT data sets, we present here a machine-learning-based approach for the automated quantification of chemical features of GBs. We trained a convolutional neural network (CNN) using twenty thousand synthesized images of grain interiors, GBs, or triple junctions. Such a trained CNN automatically detects the locations of GBs from APT data. Those GBs are then subjected to compositional mapping and analysis, including revealing their in-plane chemical decoration patterns. We applied this approach to experimentally obtained APT data sets pertaining to three case studies, namely, Ni-P, Pt-Au, and Al-Zn-Mg-Cu alloys. In the first case, we extracted GB specific segregation features as a function of misorientation and coincidence site lattice character. Secondly, we revealed interfacial excesses and in-plane chemical features that could not have been found by standard compositional analyses. Lastly, we tracked the temporal evolution of chemical decoration from early-stage solute GB segregation in the dilute limit to interfacial phase separation, characterized by the evolution of complex composition patterns. This machine-learning-based approach provides quantitative, unbiased, and automated access to GB chemical analyses, serving as an enabling tool for new discoveries related to interface thermodynamics, kinetics, and the associated chemistry-structure-property relations.
Single-crystal components made of nickel base superalloys contain pores after casting and homogenization heat treatment. Hot isostatic pressing (HIP), which is carried above the γ' -solvus temperature of the alloy, is industrially applied to reduce porosity. A modeling of HIP based on continuously distributed dislocations is developed in a 2D setting. Glide and climb of straight-edge dislocations, as well as vacancy diffusion, are the deformation mechanisms taken into account.
Thereby, dislocation glide is controlled by dragging a cloud of large atoms, and climb is controlled by vacancy diffusion. Relying on previous investigations of the creep behavior at HIP temperatures, it is assumed that new dislocations are nucleated at low-angle boundaries (LAB) and move through subgrains until they either reach the opposite LABs or react with other dislocations and annihilate.
Vacancies are created at the pore surface and diffuse through the alloy until they are either consumed by climbing dislocations or disappear at the LABs. The field equations are solved by finite elements. It is shown that pore shrinking is mostly controlled by vacancy diffusion as the shear stresses at the LABs are too low to
nucleate a sufficient amount of dislocations.
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.
The formation of pores in CMSX-4 nickel based superalloys is detrimental to the service life of the material. A way to avoid the problem is to treat the superalloys under Hot Isostatic Pressing (HIP), which enables a large volume fraction of pores to be annihilated. This paper aims to understand the contribution of plastic activity related to the gliding of dislocations on the pore annihilation. Simulations based on a phase-field model of dislocation are performed and make it possible to consider the strong anisotropy of the CMSX-4 under HIP conditions in conjunction to the strong elastic heterogeneity introduced by the pore. For pores with a radius of few micrometers, it is shown that edge parts of dislocation lines that present an extra half atomic plane oriented towards the pore are stacked above and under it in the direction which is perpendicular to their slip-planes, causing an increase of the number of dislocation along the four octahedral directions of the FCC single crystal which intersect the pore center. Results are streamlined within the isotropic elastic theory of dislocations. Effects of elastic anisotropy and dislocation reactions are also investigated in order to specify what would be the dislocation configuration around a pore in CMSX-4 under HIP conditions. Notably, the elastic anisotropy is shown to significantly modify the arrangement of dislocations close to the pore equator. Simulations also allow for the characterization of pore/dislocation interactions when dislocations are involved in Low Angle Boundaries as experimentally observed.
Rapid solidification leads to unique microstructural features, where a less studied topic is the formation of various crystalline defects, including high dislocation densities, as well as gradients and splitting of the crystalline orientation. As these defects critically affect the material’s mechanical properties and performance features, it is important to understand the defect formation mechanisms, and how they depend on the solidification conditions and alloying. To illuminate the formation mechanisms of the rapid solidification induced crystalline defects, we conduct a multiscale modelling analysis consisting of bond-order potential-based molecular dynamics (MD), phase field crystal-based amplitude expansion simulations, and sequentially coupled phase field–crystal plasticity simulations. The resulting dislocation densities are quantified and compared to past experiments. The atomistic approaches (MD, PFC) can be used to calibrate continuum level crystal plasticity models, and the framework adds mechanistic insights arising from the multiscale analysis.
This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.
Laser powder bed fusion (LPBF) is an additive manufacturing process for materials which inherently tends to yield various degrees of metastable hierarchical microstructures, defects and high residual stresses in the as-built condition depending on the process parameters. The understanding of the evolution of these typical features during heat treatment and subsequent thermal and mechanical ageing is crucial for the wider acceptance for safety critical structures. A multi-disciplinary research project at BAM studying the development of the microstructure, defects, residual stresses typical of LPBF 316L and their evolution during thermal and mechanical ageing has led to insights into the stability of these inherent features. This presentation aims to give a broad overview of the project with a few specific cases of investigation. Firstly, the formation of residual stresses, the nature of the initial microstructure, the tensile properties and a modelling approach to understand the anisotropy will be presented. This will be followed by examples of studies of their evolution during heat treatment, long term thermal exposure, and room temperature and high temperature mechanical testing compared to a baseline of conventional wrought variant of the same alloy.
Die Entwicklung digitaler Prozesse für die Materialwissenschaft und Werkstofftechnik muss naturgemäß auch die Charakterisierungsmethoden der Werkstoffprüfung abbilden, die oft durch eine hohe Komplexität gekennzeichnet sind. Als vorteilhaft erweist sich dabei der hohe Standardisierungsgrad, der sich z.B. in klaren Anforderungen an die eingesetzten Prüfmittel und festgelegten Vorgehensweisen ausdrückt. Diese können (und müssen) in entsprechenden digitalen Versuchsbeschreibungen abgebildet werden, wobei sich die klaren Datenstrukturen und Terminologien als vorteilhaft erweisen.
Porosity in single-crystal nickel-base superalloys is removed by hot isostatic pressing (HIP) at temperatures above gamma’-solvus where the material is very soft and ductile. For example, single-crystal nickel-base superalloy CMSX-4 is HIPed at temperature 1288 °C, which is slightly higher than the gamma’-solvus temperature of this alloy equal to about 1280 °C. It is assumed that pore shrinking during HIP is mostly due to dislocation creep. Such a modelling of HIP of CMSX-4 was started in our group on the base of results of creep tests of [001] single-crystals at 1288 °C [1]. However, it was found later [2] that the alloy CMSX-4 shows very strong creep anisotropy at 1288 °C. Therefore, for calibration of the creep law, creep tests of different orientations under different stress levels are required at the HIP temperature. This was the main task of present work. Single-crystals of CMSX-4 of axial orientations [001], [011], [123] and [111] were cast by VIAM Moscow and tested by BAM Berlin under creep conditions at 1288 °C and stress levels between 4 MPa and 16 MPa. At all stress levels, the creep rate increases by an order of magnitude when changing the orientation from [001] to [111] with [011] and [123] orientations in between. Such a character of creep anisotropy corresponds to the orientation dependence of the Schmid factor for octahedral glide.
The crystal viscoplasticity model developed in [1] was improved to better represent the time induced softening observed during creep. The creep tests for different stresses and orientations as well as pore closure were simulated. The results of pore closure simulation are compared with measurements of porosity decrease during Hiping.
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.
Zur Bewältigung der Herausforderung bei der Digitalisierung von Materialien und Prozessen ist eine mit allen Stakeholdern konsistente Kontextualisierung von Materialdaten anzustreben, d.h. alle erforderlichen Informationen über den Zustand des Materials einschließlich produktions- und anwendungsbezogener Änderungen müssen über eine einheitliche, maschinenlesbare Beschreibung verfügbar gemacht werden. Dazu werden Wissensrepräsentationen und Konzeptualisierungen ermöglichende Ontologien verwendet. Erste Bemühungen in den beiden Projekten Plattform Material Digital und Materials-open-Laboratory führten zur Erstellung von Anwendungsontologien, die Prozesse und Testmethoden explizit beschreiben. Dabei wurde u.a. der Zugversuch an Metallen bei Raumtemperatur nach DIN EN ISO 6892-1 ontologisch beschrieben. Diese als Beispiel dienende Ontologieentwicklung wird in dieser Präsentation vorgestellt.
From molecular dynamics simulations and the capillary fluctuation method, the solid-liquid interfacial free energy has been computed for the B2-liquid interface in the Cu-Zr system. Consistent with previous results for the FCC-liquid interface in Cu-Zr and Al-Sm but atypical of most alloys, was found to increase as the temperature is lowered. In addition, the temperature dependence was obtained for model Lennard-Jones B2-liquid alloys. In all cases the unusual temperature dependence of is correlated with an atomic structure of the interfacial region characterized by a misalignment of the number density peaks between solvents and solutes. In cases where the number density peaks are aligned, the typical temperature dependence is observed. The results are discussed in terms of the Gibbs theory of the thermodynamics of interfaces. It is proposed that the unique interfacial structure and the atypical temperature dependence of are hallmarks of an easy glass forming alloy.
Iron aluminides depict a sustainable and light-weight material class which could be employed in many applications requiring high strength at intermediate to high temperatures. According to first results, the alloy Fe-26Al-4Mo-0.5Ti-1B surpasses conventional materials in wet corrosion resistance and creep resistance up to 650 °C. For these reasons, the AiF research project “WAFEAL – Materials applications for iron aluminides” was initiated to transfer these findings into a standardised materials dataset and to derive best practices for processing. In the first place, a set of different microstructures adjusted by varying casting methods, wall thicknesses and heat treatments was investigated and correlated with hardness on macro and micro scale. Correlations were drawn between solidification rates and resulting grain sizes and hardness. The effect of vacancy hardening was only verified for wall thickness as low as 2.5 mm. Moreover, a common decrease of macrohardness after a heat treatment at 1000 °C for 100 h was observed irrespective of casting process or wall thickness. This effect was linked with an unexpected decrease of the complex boride phase fraction which acts as a hardening phase.
Die Digitalisierung von Materialien und Prozessen stellt eine große Herausforderung dar, die nur durch eine Bündelung der Bemühungen aller Beteiligten in diesem Bereich erreicht werden kann. Bei einer derartigen digitalen Beschreibung spielen Datenanalysemethoden, eine Qualitätssicherung von Prozessen inklusive Input- und Output-Daten sowie die Interoperabilität zwischen Anwendungen nach den FAIR-Prinzipien eine wichtige Rolle. Dies umfasst das Speichern, Verarbeiten und Abfragen von Daten in einer vorzugsweise standardisierten Form (Beteiligung von Normungsgremien).
Zur Bewältigung dieser Herausforderung ist eine mit allen Stakeholdern konsistente Kontextualisierung der Materialdaten anzustreben, d.h. alle erforderlichen Informationen über den Zustand des Materials einschließlich produktions- und anwendungsbezogener Änderungen müssen über eine einheitliche, maschinenlesbare Beschreibung verfügbar gemacht werden. Dazu werden Wissensrepräsentationen und Konzeptualisierungen ermöglichende Ontologien verwendet. Eine zentrale Betrachtungsweise in diesem Zusammenhang ist die Realisierung von (automatisierten) Datenpipelines, die eine Beschreibung und Verfolgung von Daten ausgehend von ihrer Erzeugung, bspw. in einem Messgerät, bis zu ihrer globalen Verwendung in möglicherweise verschiedenen Kontexten beinhalten.
Erste Bemühungen und Ansätze zu diesen Problemstellungen führten im Projekt Innovations-Plattform Material Digital (PMD, materialdigital.de) zur Erstellung von Anwendungsontologien, die Prozesse und Testmethoden explizit beschreiben. Dabei wurde u.a. der Zugversuch an Metallen bei Raumtemperatur nach ISO 6892-1 ontologisch beschrieben. Diese als Beispiel dienende Ontologieentwicklung wird in dieser Präsentation vorgestellt. Weiterhin wurde, ausgehend von der domänenspezifischen Entwicklung von Anwendungsontologien, eine Kernontologie erstellt, die eine übergeordnete Verbindung von ontologischen Konzepten aufgrund der Verwendung gleichen Vokabulars und semantischer Verknüpfungen erlaubt. Diese sowie die das PMD-Projekt selbst werden ebenfalls in dieser Präsentation vorgestellt.
The Gibbs free energy of a grain boundary is a complex thermodynamic function of temperature, pressure, and composition. These complexities add to the intrinsic crystallographic and chemical constraints imposed by the adjacent bulk phase. Recently we have proposed a density-based model for assessing grain boundary thermodynamics that enables a CALPHAD-informed description of the grain boundary. As such, the Gibbs free energy of the grain boundary is directly linked with available CALPHAD thermodynamic data. In this talk, new aspects of interfacial segregation and phase transformation are revealed by benchmarking the current model for various experimental cases, including several steels, high-entropy alloys and aluminum alloys. The effects of elastic interactions on the grain boundary segregation and the application of the model to a nanocrystalline Pt-Au alloy, with numerous grain boundaries of various characters, will be discussed.
Due to the diversity of materials and the processes associated with their production and use, the complexity of the lifecycles of materials and the multitude of academic and industrial researchers participating in generation of data for material design impose a huge challenge. The topical goal of digitalizing materials and processes can only be adequately addressed by consolidating the efforts of all stakeholders in this field. There are many scattered activities, but there is a demand for an elimination of redundancies as well as an advance in acceptance and a common basis in the digitalization of materials. Furthermore, data analysis methods play an important role in both, the experimental and simulation-based digital description of materials, but they have been poorly structured so far.
Therefore, the two joint projects Platform Material Digital (PMD, materialdigital.de) and Materials open Laboratory (Mat-o-Lab, matolab.de) aim to contribute to a standardized description of data processing methods in materials research. Besides stimulating the formation of a collaborative community in this respect, their main technical goals are the quality assurance of the processes and the output data, the acquisition and definition of their accuracy as well as the interoperability between applications. In this regard, data management in accordance with the FAIR (findability, accessibility, interoperability, reuseability) principles is addressed. There is a common agreement in the scientific community following current discussions that data is supposed to be conform to these principles. This includes storage, processing and querying of data in a preferably standardized form.
To meet the challenge to contextualize material data in a way that is consistent with all stakeholders, all necessary information on the condition of the material including production and application-related changes have to be made available via a uniform, machine-readable description. For this purpose, ontologies are to be used since they allow for machine-understandable knowledge representations and conceptualizations that are needed for data management and the digitalization in the field of materials science.
As first efforts in PMD and Mat-o-Lab, application ontologies are created to explicitly describe processes and test methods. Thereby, the well-known tensile test of metals at room temperature was described ontologically in accordance with the respective ISO standard 6892-1:2019-11.
The efforts in creating this tensile test application ontology are shown in this presentation. Especially, the path of ontology development based on standards to be pursued is focused, which is in accordance with the generic recommendations for ontology development and which is supposed to be exemplary for the creation of other application ontologies.
The large number of TEM investigations and the regular microstructure
of single-crystal nickel-base superalloys has boosted the development of a number of physically motivated constitutive laws. In contrast to the more phenomenological models discussed in the next chapter, these models use dislocation densities as internal variables. Obvious advantages are that the computed densities can be compared to TEM observations and the Deformation mechanisms can be easier translated into mathematical equations.
The elastic constants are the most basic mechanical properties of a material and are needed for any structural analysis of a component. For example, they have a major influence on the eigenfrequencies of vibrating parts. Single crystals of Ni-base superalloys are strongly anisotropic, which means that the observed properties are orientation dependent. Tensor algebra is then required to mathematically formulate the elastic properties and their relations to the crystal orientation. Hence, this chapter first summarizes some basic definitions and calculation rules for Rotation matrices, including the definition of the Euler angles, which are most commonly used to define the relative orientations of the crystal and the component. Parts of this chapter closely follow the lines of the excellent exposition of the topic by Olschewski.
The elastic energy of mixing for multi-component solid solutions is derived by generalizing Eshelby's sphere-in-hole model. By surveying the dependence of the elastic energy on the chemical composition and lattice misfit, we derive a lattice strain coefficient λ*. Studying several high-entropy alloys and superalloys, we propose that most solid solution multi-component alloys are stable when λ*<0.16, generalizing the Hume-Rothery atomic-size rule for binary alloys. We also reveal that the polydispersity index δ, frequently used for describing strain in multi-component alloys, directly represents the elastic energy e with e=qδ², q being an elastic constant. Furthermore, the effects of (i) the number and (ii) the atomic-size distribution of constituting elements on the phase stability of high-entropy alloys were quantified. The present derivations and discussions open for richer considerations of elastic effects in high-entropy alloys, offering immediate support for quantitative assessments of their thermodynamic properties and studying related strengthening mechanisms.
Thermal cycling of a Ni-excess NiTi alloy was conducted between 50 °C and liquid nitrogen temperature to induce martensitic transformations and to reverse them after. The starting point was an annealed and slowly cooled state, the end point a sample thermally cycled 1500 times. Positron annihilation lifetime spectra and Coincidence Doppler Broadening profiles were obtained in various states and at various tem- peratures. It was found that the initial state was low in defects with positron lifetimes close to that of bulk NiTi. Cycling lead to a continuous build-up of a defect structure up to 20 0 −50 0 cycles after which saturation was reached. Two types of defects created during cycling were identified, namely pure dislo- cations and vacancies attached to dislocations.
Ti-6Al-4V alloy is intensively used in the aerospace industry because of its high specific strength. However, the application of Laser Powder Bed Fusion (LPBF) Ti-6Al-4V alloy for structurally critical load-bearing components is limited. One of the main limiting factors affecting the structural integrity, are manufacturing defects. Additionally, the high cooling rates associated with LPBF process result in the formation of large residual stress (RS) with complex fields. Such RS can cause cracking and geometrical distortions of the part even right after production. Also, the microstructure of LPBF Ti-6Al-4V in the as-built condition is significantly different from that of the conventionally produced alloy. All these factors affect the mechanical behavior of the material. Therefore, to improve the material performance it is important to evaluate the individual effect of RS, defects, and microstructure on fatigue life. To this aim Ti-6Al-4V LPBF material in as-built condition and subjected to different post-processing, including two heat treatments (for stress relief and microstructural modification) and Hot Isostatic Pressing (HIP, for densification), were investigated.
Prior to fatigue tests at elevated temperature, the microstructure, the mesostructure, and subsurface RS on the fatigue samples were investigated. It was found that the fatigue performance of HIPped samples is similar to that of conventionally produced Ti-6Al-4V. The tensile RS found at the surface of as-built samples decreased the fatigue life compared to heat-treated samples. Additionally, the modification of the microstructure (by heat treatment) did not affect the fatigue performance in the regime of mostly elastic strain. This shows that in the absence of tensile RS the manufacturing defects solely control the failure of LPBF components and densification has the strongest effect on the improvement of the mechanical performance.
A γ-analogue of the superalloy CMSX-4 that does not contain the strengthening γ′ -phase and only consists of the γ-solid solution of nickel has been designed, solidified as single-crystals of different orientations, and tested under creep conditions in the temperature range between 1150 and 1288 °C. The tests have revealed a very high creep anisotropy of this alloy, as was previously found for CMSX-4 at supersolvus temperature of 1288 °C. This creep anisotropy could be explained by the dominance of 〈011〉{111} octahedral slip. Furthermore, the analysis of the creep data has yielded a high value of the creep activation energy, Qc≈442 kJ/mol, which correlates with the high activation energy of Re diffusion in Ni. This supports the hypothesis that dislocation motion in the γ-matrix of Re-containing superalloys is controlled by the diffusion of the Re atoms segregating at the dislocation core. The Norton stress exponent n is close to 5, which is a typical value for pure metals and their alloys. The absence of γ′ -reprecipitation after high-temperature creep tests facilitates microstructural investigations. It has been shown by EBSD that creep deformation results in an increasing misorientation of the existing low angle boundaries. In addition, according to TEM, new low angle boundaries appear due to reactions of the a/2 〈011〉 mobile dislocations and knitting of new networks.
The phase-like behavior of grain boundaries (GBs), recently evidenced in several materials, is opening up new possibilities in the design of alloy microstructures. In this context, GB phase diagrams are contributing to a predictive description of GB segregation and (interfacial) phase changes. The influence of chemo-mechanical solute-GB interactions on the GB phase diagram remains elusive so far. This is particularly important for multi-component alloys where the elastic interactions among solute atoms, of various sizes and bonding energies, can prevail, governing a complex co-segregation phenomenon. Recently, we developed a density-based model for GB thermodynamics that intrinsically accounts for GB elasticity in pure elements. In this work, we incorporate the homogeneous and heterogeneous elastic energies associated with the solutes into the density-based framework. We derive the multi-component homogeneous elastic energy by generalizing the continuum misfitting sphere model and extend it for GBs. The density-based free energy functional directly uses bulk CALPHAD thermodynamic data. The model is applied to binary and ternary Al alloys. We reveal that the elastic energy can profoundly affect the GB solubility and segregation behavior, leading to Cu segregation in otherwise Cu-depleted Al GBs. Consequently, GB segregation transition, i.e., a jump in the GB segregation as a function of alloy composition, is revealed in Al-Cu and Al-Cu-Mg alloy systems with implications for subsequent GB precipitation in these alloys. CALPHAD-informed elasticity-incorporated GB phase diagrams enable addressing a broader range of GB phenomena in engineering multi-component alloys.
Data analysis methods play an important role in both the experimental and simulation-based digital description of materials but have so far been poorly structured. The platform Material Digital (PMD) is supposed to contribute to a standardized description of data processing methods in materials research. The goal is the quality assurance of the processes and the output data, the acquisition and definition of their accuracy as well as the interoperability between applications.
Therefore, application ontologies are created to explicitly describe processes and test methods. In this presentation, the first efforts within the joint project PMD in creating a tensile test application ontology in accordance with the ISO standard 6892-1:2019-11 are shown. Especially, the path of ontology development to be pursued based on standards was focused. Furthermore, the presentation includes a live demonstration of queries possibly performed to query data that was uploaded in the PMD triple store.
For more than half a century, spinodal decomposition has been a key phenomenon in considering the formation of secondary phases in alloys. The most prominent aspect of the spinodal phenomenon is the lack of an energy barrier on its transformation pathway, offering an alternative to the nucleation and growth mechanism. The classical description of spinodal decomposition often neglects the influence of defects, such as grain boundaries, on the transformation because the innate ability for like-atoms to cluster is assumed to lead the process. Nevertheless, in nanocrystalline alloys, with a high population of grain boundaries with diverse characters, the structurally heterogeneous landscape can greatly influence the chemical decomposition behavior. Combining atom-probe tomography, precession electron diffraction and density-based phase-field simulations, we address how grain boundaries contribute to the temporal evolution of chemical decomposition within the miscibility gap of a Pt-Au nanocrystalline system. We found that grain boundaries can actually have their own miscibility gaps profoundly altering the spinodal decomposition in nanocrystalline alloys. A complex realm of multiple interfacial states, ranging from competitive grain boundary segregation to barrier-free low-dimensional interfacial decomposition, occurs with a dependency upon the grain boundary character.
Initially, as-cast and homogenized single crystals of nickel-base superalloy CMSX-4 are subjected to hot isostatic pressing at 1288 °C. Two series of experiments are conducted: under the same pressure of 103 MPa but with different durations, between 0.5 and 6 h, and under different pressures, between 15 and 150 MPa, but for the same time of 0.5 h. The porosity annihilation is investigated metallographically and by high-resolution synchrotron X-ray tomography. The obtained experimental results are compared with the predictions of the vacancy model proposed recently in the group. Herein, the model is further refined by coupling with X-ray tomography. The model describes the evolution of the pore arrays enclosed in the 3D synchrotron tomograms during hot isostatic pressing and properly predicts the time and stress dependences of the pore annihilation kinetics. The validated model and the obtained experimental results are used for selecting the optimal technological parameters such as applied pressure and processing time
This presentation shows some experimental results of the characterization of the creep behavior of LPBF 316L, which has been poorly studied and understood to date. The presentation includes results regarding the mechanical properties, the initial microstructural state and its evolution under loading, and the damage mechanism. This work was done within the BAM focus area materials project AGIL. As a benchmark to assess the material properties of the LPBF 316L, a conventionally manufactured variant was also tested.
The underlying cause of mechanical anisotropy in additively manufactured (AM) parts is not yet fully understood and has been attributed to several different factors like microstructural defects, residual stresses, melt pool boundaries, crystallographic and morphological textures.
To better understand the main contributing factor to the mechanical anisotropy of AM stainless steel 316L, bulk specimens were fabricated via laser powder bed fusion (LPBF).
Tensile specimens were machined from these AM bulk materials for three different inclinations relative to the build plate. Dynamic Young's modulus measurements and tensile tests were used to determine the mechanical anisotropy. Some tensile specimens were also subjected to residual stress measurement via neutron diffraction, porosity determination with X-ray micro-computed tomography, and texture analysis with electron backscatter diffraction (EBSD). A crystal plasticity model was used to analyze the elastic anisotropy and the anisotropic yield behavior of the AM specimens, and it was able to capture and predict the experimental behavior accurately. Overall, it was shown that the mechanical anisotropy of the tested specimens was mainly influenced by the crystallographic texture.
The cyclic crack tip opening displacement ΔCTOD is a promising loading Parameter to quantify the crack propagation under thermomechanical fatigue (TMF). In this work, suitable techniques are investigated and compared for an accurate calculation of ΔCTOD under TMF loading using a viscoplastic temperature dependent material model.
It turned out that collapsed special crack tip elements give the best results. An efficient FEM-technique is developed to simulate the incremental crack growth by successive remeshing, whereby the deformations and internal state variables are mapped from the old mesh onto the new one. The developed techniques are demonstrated and discussed for two-dimensional examples like TMF-specimens. Recommendations are made regarding important numerical control parameters like optimal size of crack tip elements, length of crack growth increment in relation to plastic zone size and ΔCTOD value.
The cyclic crack tip opening displacement ΔCTOD is a promising loading Parameter to quantify the crack propagation under thermomechanical fatigue (TMF). In this work, suitable techniques are investigated and compared for an accurate calculation of ΔCTOD under TMF loading using a viscoplastic temperature dependent material model.
It turned out that collapsed special crack tip elements give the best results. An efficient FEM-technique is developed to simulate the incremental crack growth by successive remeshing, whereby the deformations and internal state variables are mapped from the old mesh onto the new one. The developed techniques are demonstrated and discussed for two-dimensional examples like TMF-specimens. Recommendations are made regarding important numerical control parameters like optimal size of crack tip elements, length of crack growth increment in relation to plastic zone size and ΔCTOD value.
The discovery of the high entropy concept at the beginning of the 3rd millennium lead to a worldwide increase in metallurgical research, as the possible element combinations seemed nearly endless and the range of applications wide. In the early years of research, one of the main goals was the discovery of a single-phase high entropy alloy. As research evolved, it was found that properties could be enhanced by opening the HE-concept towards multiphase alloys, and from the wide area of possibilities our group chose a tuning of the properties towards high temperature application.
Compositionally complex Al10Co25Cr8Fe15Ni36Ti6 alloy, which is single-phase at high temperature, around 1200°C, shows a three phase morphology at intermediate temperatures, around 800°C. A high temperature homogenization procedure has to be applied in order to decrease the segregation induced by the dendritic growth. Subsequent annealing promotes the formation of the strengthening γ' precipitates. The alloy shows a positive lattice misfit between the γ and the γ' phase, which can be an indicator for good creep properties.
The microstructure can be optimized by adding trace elements such as Mo and Hf, known as γ and γ' strengtheners in Ni-based superalloys, respectively. Atom probe measurements show that Mo segregates into the γ matrix, and Hf prefers the γ' precipitates, where it increases the lattice parameter and thus also the lattice misfit, by about 50%. The alloy family shows interesting mechanical properties, especially the Al9.5Co25Cr8Fe15Ni36Ti6Hf0,5 alloy – its tensile properties are better than those of commercial Alloy 800H and IN617 at temperatures up to 700°C.
Data analysis methods play an important role in both the experimental and simulation-based digital description of materials but have so far been poorly structured. The platform Material Digital (PMD) should contribute to a standardized description of data processing methods in materials research. The goal is the quality assurance of the processes and the output data, the acquisition and definition of their accuracy as well as the interoperability between applications.
Therefore, application ontologies are created to explicitly describe processes and test methods. In this presentation, the first efforts in creating a tensile test application ontology in accordance with the ISO standard 6892-1:2019-11 are shown. Especially, the path of ontology development to be pursued based on standards was focused.
The cyclic crack tip opening displacement ΔCTOD is a promising loading Parameter to quantify the crack propagation under thermomechanical fatigue (TMF). In this work, suitable techniques are investigated and compared for an accurate calculation of ΔCTOD under TMF loading using a viscoplastic temperature dependent material model.
It turned out that collapsed special crack tip elements give the best results. An efficient FEM-technique is developed to simulate the incremental crack growth by successive remeshing, whereby the deformations and internal state variables are mapped from the old mesh onto the new one. The developed techniques are demonstrated and discussed for two-dimensional examples like TMF-specimens. Recommendations are made regarding important numerical control parameters like optimal size of crack tip elements, length of crack growth increment in relation to plastic zone size and ΔCTOD value.
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.
Manufacturing defects, high residual stress (RS), and microstructures affect the structural integrity of laser powder bed fusion (LPBF) Ti-6Al-4V. In this study, the individual effect of these factors on fatigue performance at elevated temperature (300 °C) was evaluated. Material in as-built condition and subjected to post-processing, including two heat treatments and hot isostatic pressing, was investigated. It was found that in the absence of tensile RS, the fatigue life at elevated temperature is primary controlled by the defects; and densification has a much stronger effect than the considered heat treatments on the improvement of the mechanical performance.
Interfacial Spinodals
(2021)
Despite their finite spatial extent, interfaces can have profound impacts on microstructure properties. This is because of their distinct phase-like properties distinguishing them from the adjacent homogeneous bulk structure. When noticed by solute atoms, interfaces can experience their own chemical phase changes. In this talk, we investigate the constrained states of chemically decomposed phases at interfaces. A density-based theory of interfaces is proposed to describe the confined chemical decomposition at general grain boundaries. Here the grain boundary is viewed as a lesser dense, defected structure with reference to the corresponding bulk structure. Using this picture, the thermodynamic origins of interfacial spinodal phenomena are revealed. We also show that transient interfacial spinodals can be activated over a large alloy composition range, enabling kinetic engineering of interfacial chemistry.
Systematic microstructure design requires reliable thermodynamic descriptions and phase diagrams of each and all microstructure elements. While such descriptions are well established for most bulk phases, thermodynamic assessment of crystal defects is greatly challenged by their individualistic aspects. In this talk, we present a density-based thermodynamic concept to describe defects based on available bulk thermodynamic data. Here dealing with grain boundaries (GBs), we apply this concept to compute GB (phase) diagram. Applications to segregation engineering of GBs in bulk and nanocrystalline alloys will be presented. We further develop this model to include the effect of elastic interactions due to atom size mismatch and obtain the corresponding GB (phase) diagram for the ternary Al-Cu-Li system.
The onset of plasticity in a single crystal C60 fullerite was investigated by nanoindentation on the (111) crystallographic plane. The transition from elastic to plastic deformation in a contact was observed as pop-in events on loading curves. The respective resolved shear stresses were computed for the octahedral slip systems ⟨011¯¯¯⟩{111}, supposing that their activation resulted in the onset of plasticity. A finite element analysis was applied, which reproduced the elastic loading until the first pop-in, using a realistic geometry of the Berkovich indenter blunt tip. The obtained estimate of the C60 theoretical shear strength was about 1/11 of the shear modulus on {111} planes.
With an increasing demand in more efficient fuel consumption to reduce CO2 emissions, weight reductions in high-temperature materials at affordable costs gain increasing attention. One potential candidate is the intermetallic material class of iron aluminides, combining the advantages in mass savings, high temperature performance and recyclability of resources. The alloy Fe-26Al-4Mo-0.5Ti-1B was selected to study the microstructural features evolving from two casting processes, five wall thicknesses and three final conditions. Conclusions are drawn upon the correlations of processing variables, grain sizes and hardness.
A phase field model of brittle fracture has been developed to simulate the Hertzian crack induced by penetration of a rigid sphere to an isotropic linear-elastic half-space. The fracture formation is regarded as a diffusive field variable, which is zero for the intact material and unity if there is a crack. Crack growth is assumed to be driven by a strain invariant. The numerical implementation is performed with the finite element method and an implicit time integration scheme. The mechanical equilibrium and the phase field equations are solved in a staggered manner, sequentially updating the displacement field and the phase field variable. Numerical examples demonstrate the capability of the model to reproduce the nucleation and growth of the Hertzian cone crack.
The effectiveness of the mechanism of precipitation strengthening in metallic alloys depends on the shapes of the precipitates. Two different material systems are considered: tetragonal γ′′ precipitates in Ni-based alloys and tetragonal θ′ precipitates in Al-Cu-alloys. The shape formation and evolution of the tetragonally misfitting precipitates was investigated by means of experiments and phase-field simulations. We employed the method of invariant moments for the consistent shape quantification of precipitates obtained from the simulation as well as those obtained from the experiment. Two well-defined shape-quantities are proposed: (i) a generalized measure for the particles aspect ratio and (ii) the normalized λ2, as a measure for shape deviations from an ideal ellipse of the given aspect ratio. Considering the size dependence of the aspect ratio of γ′′ precipitates, we find good agreement between the simulation results and the experiment. Further, the precipitates’ in-plane shape is defined as the central 2D cut through the 3D particle in a plane normal to the tetragonal c-axes of the precipitate. The experimentally observed in-plane shapes of γ′′-precipitates can be quantitatively reproduced by the phase-field model.
Simulation of the θ′ Precipitation Process with Interfacial Anisotropy Effects in Al-Cu Alloys
(2021)
The effects of anisotropic interfacial properties and heterogeneous elasticity on the growth and ripening of plate-like θ′-phase (Al2Cu) in Al-1.69 at.% Cu alloy are studied. Multi-phase-field simulations are conducted and discussed in comparison with aging experiments. The precipitate/matrix interface is considered to be anisotropic in terms of its energy and mobility. We find that the additional incorporation of an anisotropic interfacial mobility in conjunction with the elastic anisotropy result in substantially larger aspect ratios of the precipitates closer to the experimental observations. The anisotropy of the interfacial energy shows comparably small effect on the precipitate’s aspect ratio but changes the interface’s shape at the rim. The effect of the chemo-mechanical coupling, i.e., the composition dependence of the elastic constants, is studied as well. We show that the inverse ripening phenomenon, recently evidenced for δ’ precipitates in Al-Li alloys (Park et al. Sci. Rep. 2019, 9, 3981), does not establish for the θ′ precipitates. This is because of the anisotropic stress fields built around the θ′ precipitates, stemming from the precipitate’s shape and the interaction among different variants of the θ′ precipitate, that disturb the chemo-mechanical effects. These results show that the chemo-mechanical effects on the precipitation ripening strongly depend on the degree of sphericity and elastic isotropy of the precipitate and matrix phases.