5 Werkstofftechnik
Filtern
Erscheinungsjahr
- 2019 (55) (entfernen)
Dokumenttyp
- Zeitschriftenartikel (55) (entfernen)
Sprache
- Englisch (55)
Schlagworte
- Corrosion (7)
- Carbon steel (3)
- Crystallization (3)
- 3D printing (2)
- Additive Manufacturing (2)
- Additive manufacturing (2)
- Bioactive glass (2)
- Condensate (2)
- Corrosion Fatigue (2)
- Degradation (2)
- Ductile iron (2)
- Fatigue (2)
- High Alloyed Steel (2)
- Impurities (2)
- NMR spectroscopy (2)
- Niobium alloying (2)
- Oxidation (2)
- Pitting (2)
- AISI 304L (1)
- Abrasion (1)
- Alkali-activated materials (1)
- Alumina (1)
- Aluminosilicate glasses (1)
- Aquifer (1)
- Artificial weathering (1)
- Bioceramics (1)
- Biodiesel (1)
- Biogeochemical cycling (1)
- Biomineralisation (1)
- Biopolymer (1)
- Bubble formation (1)
- C. lap-shear (1)
- CCS (1)
- CCUS (1)
- CFRP (1)
- CO2 (1)
- CO2 separation membranes (1)
- Calcination (1)
- Calcium cobaltite (1)
- Carbidic austempered ductile iron (1)
- Carbon capture (1)
- Carbon capture, utilization and storage technology (1)
- Carbon fibres (1)
- Carbon storage (1)
- Cavitation (1)
- Cellulose (1)
- Ceramic (1)
- Ceramics (1)
- Chalcogenides (1)
- Characterisation (1)
- Coefficient of thermal expansion (1)
- Contact angle (1)
- Contact fatigue (1)
- Copper vacancies (1)
- Corrosion pits (1)
- Crack arrest (1)
- Crack propagation (1)
- Crosslinking (1)
- Crystal Texture (1)
- Cyclic softening (1)
- D. aging (1)
- D. creep D. viscoelasticity (1)
- Defects (1)
- Deuterium (1)
- Dielectric breakdown (1)
- Diesel (1)
- Diesel Fuel (1)
- Distributed fiber optic sensing (1)
- EBSD (1)
- Early oxidation (1)
- Early sulfidation (1)
- Elastic constants (1)
- Electrochemical characterisation (1)
- Electrochemical deposition (1)
- Electrochemical impedance spectroscopy (1)
- Electron energy (1)
- Electron microscopy (1)
- Endurance Limit (1)
- Energy distribution (1)
- Environment (1)
- Environmentally assisted cracking (1)
- Exposed metal sites (1)
- FSDC (1)
- Fabrication (1)
- Facilitated activation (1)
- Fatigue Testing (1)
- Fatigue crack propagation stages (1)
- Ferritic steels (1)
- Ferritic–martensitic steel (1)
- Finite element analysis (1)
- Four-point bending test (1)
- Fracture (1)
- Fracture mechanics (1)
- Freeze casting (1)
- Friction Stir Welding (1)
- Frozen state photopolymerization (1)
- GFRP (1)
- Geothermal (1)
- Glass (1)
- Glass-ceramic (1)
- Gold (1)
- Grain boundary (1)
- Heat treatment (1)
- Hierarchical porosities (1)
- High pressure (1)
- High temperature corrosion (1)
- High-temperature oxidation (1)
- High-temperature properties (1)
- High-voltage testing (1)
- Hydrogel (1)
- Hydrogen (1)
- Hydrogen diffusivity (1)
- Hygrothermal (1)
- Impact damage (1)
- In-situ Process Monitoring (1)
- Inclusion cluster (1)
- Inclusion size (1)
- Inconel 625 (1)
- Incremental lifetime models (1)
- Infrared nano AFM (1)
- Infrared spectroscopy (1)
- Intermodulation AFM (1)
- Internal Surfaces (1)
- Internal oxidation (1)
- Interphase (1)
- Ionic porosity (1)
- Iron meteorite (1)
- Kikuchi pattern (1)
- LSD print (1)
- Laser beam melting (1)
- Laser-induced slip casting (1)
- Layerwise slurry deposition (1)
- Long-term storage (1)
- Low cycle fatigue (1)
- MOF-74 (1)
- Magmatic and hydrothermal processes (1)
- Martensite (1)
- Mass transport (1)
- Material degradation (1)
- Micro-shrinkages (1)
- Microhardness (1)
- Mis-match (1)
- Mixed Ca-K-Na phosphates (1)
- Mixed-linkers (1)
- Moisture (1)
- Multiple cracks (1)
- Na and K rhenanites (1)
- Nanocomposites (1)
- Natural (1)
- Neutron diffraction (1)
- Nitride (1)
- Non-destructive Materials (1)
- Non-metallic inclusions (1)
- Orientation relationship (1)
- Oxidation protection (1)
- P92 (1)
- PE-HD Sorption (1)
- Parabolic flight (1)
- Permeability (1)
- Phase diagram (1)
- Phase transformations (1)
- Phase-field (1)
- Phosphate (1)
- Pitting corrosion (1)
- Plastic deformation (1)
- Platinum-group-metals (1)
- Polyaniline (1)
- Polymer (1)
- Polyurethane (1)
- Pores (1)
- Preceramic polymer (1)
- Pressure-assisted sintering (1)
- Process development (1)
- Processing window (1)
- Pultruded fiber rods (1)
- Relaxation fatigue (1)
- Resonance testing (1)
- Roughness (1)
- SDC (1)
- STEM (1)
- Safety (1)
- Samarium doped ceria (1)
- Sandwich (1)
- Scaffolds (1)
- Scavenging effect of iron (1)
- Scratches (1)
- Silicoborate glasses (1)
- Silicon Carbide (1)
- Simulation (1)
- Sintering (1)
- Slip-rolling (1)
- Soda-lime-silica (1)
- Soda-lime-silica glass (1)
- Sodium ion batteries (1)
- Sol-gel coating (1)
- Sorption (1)
- Spar cap design (1)
- Standardisation (1)
- Statistics (1)
- Steel (1)
- Stress intensity factor (1)
- Stress-strain behavior (1)
- Structural composites (1)
- Structural defects (1)
- Structural health monitoring (1)
- Subcritical crack growth (1)
- Sulfidation (1)
- Superconducting magnet (1)
- Surface (1)
- Surface treatments (1)
- Swept wavelength interferometry (1)
- Synthesis (1)
- Thermoelectric properties (1)
- Thiol-ene click chemistry (1)
- ToF-SIMS (1)
- Tungsten-Rhenium (1)
- Utilization, and storage (CCUS) technology (1)
- Vickers indentation (1)
- Viscoelastic model (1)
- Viscous sintering (1)
- WAXS (1)
- Water content (1)
- Water speciation (1)
- Wetting (1)
- X-ray absorption spectroscopy (1)
- X-ray refraction (1)
- Young´s modulus (1)
- ZnO (1)
- arbidic austempered ductile iron (1)
- bioactive (1)
- biomaterials (1)
- bone (1)
- high pressure (1)
- infrared spectroscopy (1)
- phosphate glasses (1)
- water speciation (1)
- µ-gravity (1)
Organisationseinheit der BAM
- 5 Werkstofftechnik (55) (entfernen)
An investigation of the two-component phase diagram of the CaNaPO4- CaKPO4system performed using various analysis techniques is reported. The continuous solid solution series of α-CaMPO4 existing above 700 °C undergoes eutectoid decomposition during cooling to β-CaMPO4-based solid solutions enriched with Na and K, and to an intermediate nonstoichiometric compound with an ideal composition of CaK0.6Na0.4PO4. All three compounds exhibit significant volumetric effects associated with first-order phase transitions, with positive volume changes under cooling for the intermediate compound. Increased K content in ceramics based on CaKyNa1-yPO4 compositions enhances the strength properties of those ceramics, including their fracture toughness, which is associated with increased density. Increased K content also has a smaller effect of inducing phase transformations accompanied by strong volume changes.
The physical and chemical effects of diesel and biodiesel fuels on two high-density polyethylene (PE-HD) types were investigated. Both semi-crystalline PE-HD are common thermoplastic materials for container and storage tank applications. Biodiesel, a composition of unsaturated fatty acid esters from renewable resources, was chosen as it is regarded a possible green alternative to fossil fuels. The study aims at identifying significant differences between biodiesel and conventional diesel fuels based on the differences in the chemical nature of the two. The physical effects of the fuels on the polymer at first comprises the sorption behavior, i.e. kinetics and final equilibrium concentration. Not only are both fuels absorbed by the amorphous phase of the semi-crystalline PE-HD, they also induce a plasticization effect that modifies the molecular mobility and therefore also the characteristic yielding properties, manifest in the obtained stress-strain curves. The chemical effects related to degradation phenomena is investigated by a long-term storage scenario using partially immersed tensile test specimens in diesel and biodiesel. We were able to confirm the proposed co-oxidation mechanism by Richaud et al. for polyethylene-unsaturated penetrant systems on a larger scale based on practical tensile tests. One of the investigated polyethylene grades subjected to tensile drawing showed a significant loss of plastic deformation and the onset of premature failure after 150 days of storage in biodiesel. Further biodiesel storage showed a systematically reduced elongation at break before necking. None of these effects were observed in diesel. Oxidation of fuels and polymer after progressing storage times were analyzed by the evolution of carbonyl species in FT-IR/ATR spectroscopy.
Modelling of environmentally assisted material degradation in the crack phase-field framework
(2019)
The simulation of crack propagation was conducted with a diffusive crack model in a variational framework. Moreover, the physically sound introduction of mass transport and coupling mechanisms due to environmentally assisted effects could be realised in this framework. The objective consists of the application of the phase-field Approach towards the simulation of environmentally assisted material degradation with the advantage of a non-required predefined crack path and a mesh-independent non-local formulation that facilitates the damage evolution with respect to material softening. The sharp crack is regularised by the introduction of a phase-field order parameter leading to a diffusive crack formulation.
Besides the equations originating from the linear momentum balance an additional evolution equation for the crack phase-field is introduced. Furthermore, mass transport is simulated by a Diffusion equation. The description delivered by the variational phase-field framework is able to simulate crack propagation according to published numerical test cases.
Additionally, the calculation of stress intensity factors is possible as well as crack resistance curves that describe stable crack propagation.
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.
Dense ZnO films with a strong c‐axis texture have been deposited on transparent conductive oxide glass, glass, and Si wafers, respectively, with a two‐step pressureless wet chemical method using zinc acetate dihydrate as Zn‐precursor. The crystallographic structure of the films has been studied with XRD and scanning electron microscopy. Optical measurements reveal a high transparency of the ZnO films with a thickness of up to 10 μm. This new cost‐effective route for ZnO film deposition does not require expensive sophisticated equipment and is easily upscaled.
The prediction of structural parameters and optoelectronic properties of compound semiconductors is very important. However, calculations often neglect chemical variability and structural defects. In chalcopyrite type semiconductors one of the major defects are copper vacancies (V Cu). The four cation neighbors of the anion determine its position in the chalcopyrite type structure expressed by the Wyckoff position 8d (x, 1/4, 1/8). Intrinsic point defects like V
Cu and anti-sites may cause variations of the Anion position in the middle of the cation tetrahedron, especially in the Anion position Parameter x. For stoichiometric chalcopyrite type compounds a formalism according to the principle of conservation of tetrahedral bonds (CTB) can be applied to calculate the anion position parameter, but it fails in the case of off-stoichiometric chalcopyrites. This case study of chalcopyrite type CuGaS 2 and Mn-substituted GuGaS 2
shows that the experimentally determined anion position Parameter x
deviate from values calculated by CTB approach. The systematic investigation of off-stoichiometric CuGaS 2 and Mn-substituted GuGaS
2 demonstrates the effect of copper vacancies on the average radii of the cation sites (Wyckoff positions 4a and 4b) as well as on the anion position Parameter x. By applying an elaborated CTB Approach implementing copper vacancies an agreement between experimental and calculated anion position Parameter x can be obtained.
Carbidic Austempered Ductile Iron (CADI) microstructures containing eutectic carbides can be produced by the addition of carbide stabilizing elements, such as chromium. Carbides formed from the addition of Cr are eutectic of M3C type. The presence of such hard phases can enhance the abrasion wear resistance of ductile iron. A new CADI can be produced by the addition of Nb. Niobium carbide particles are formed in the beginning of solidification and remain stable once they are insoluble in solid iron matrix. The dry sand abrasive wear resistance of ductile irons alloyed with 1.0, 1.8, and 2.4 wt% Nb were tested in both “as-cast” and “heat treated” conditions using standard ASTM G65. Results were compared to abrasive wear data obtained on ductile iron alloyed with 1 wt% Cr, CADI (1 wt% Cr), and the basic composition of iron without carbide stabilizing elements. In the “ascast” condition, the addition of Nb did not lead to a reduction in wear, while CADI with Nb is a promising substitute for CADI with Cr addition, because both materials showed very similar values of abrasion resistance.
Micro-ploughing and micro-cutting mechanisms were observed on the worn surfaces of ductile irons. Abrasive wear resistance of these alloys was correlated with the volume fraction of carbides.
The aim of this research is to study the influence of moisture absorption at low moisture contents on the creep behaviour of an epoxy adhesive in steel bonded joints. Single lap joints were manufactured using high strength steel adherends and a two-component epoxy adhesive. The single lap joints were tested at load Levels corresponding to average lap shear stresses of±5%, 15%, 30% and 45% of the dry lap shear strength in both 40 °C air and 40 °C distilled water. Specimens were not pre-aged to be able to analyse the coupled effect of moisture and loading. The test results show that an increase in the load level resulted in an increase in the instantaneous strain and in the creep strain rate. The creep strain of single lap joints loaded in water was generally larger than for the ones loaded in air. For joints loaded in water the creep behaviour was found to be dependent on the moisture concentration in the adhesive. At low moisture percentages creep was suppressed, resulting in a lower instantaneous strain. At higher moisture percentages creep was promoted, resulting in a larger strain rate. The suppression of creep at low moisture percentages is attributed to water molecules bonding to the epoxy macromolecules, resulting in a reduction in molecular mobility and a smaller creep strain. At higher moisture percentages the plasticizing effect of the water dominates, resulting in a larger creep strain. The Maxwell threeelement solid model and Kelvin-Voigt three-element solid model were used to simulate the creep behaviour of the single lap joints loaded in air and water. The models gave good representations of the creep Response across the different load levels in both water and air, they were however unable to give a correct representation of the instantaneous strain of the single lap joints loaded in water. This is attributed to the models being unable to account for the present short-term relaxation process that is dependent on the moisture concentration.
Computational methods for lifetime prediction of metallic components under high-temperature fatigue
(2019)
The issue of service life prediction of hot metallic components subjected to cyclic loadings is addressed. Two classes of lifetime models are considered, namely, the incremental lifetime rules and the parametric models governed by the fracture mechanics concept. Examples of application to an austenitic cast iron are presented. In addition, computational techniques to accelerate the time integration of the incremental models throughout the fatigue loading history are discussed. They efficiently solve problems where a stabilized response of a component is not observed, for example due to the plastic strain which is no longer completely reversed and accumulates throughout the fatigue history. The performance of such an accelerated Integration technique is demonstrated for a finite element simulation of a viscoplastic solid under repeating loading–unloading cycles.
The use of high niobium alloyed cast iron alloys is a relatively new approach in which the niobium addition intends to improve the properties of the material by the precipitation of hard niobium carbides during solidification. Steels can be replaced by ductile cast iron in some rolling applications, such as gears and cams, in order to reduce material costs. The aim of this work is to evaluate ductile iron alloyed with 1 weight percent (wt.%) niobium for the as cast specimens and with 1.8 wt.% and 2.4 wt.% niobium for the austempered specimens under lubricated slip-rolling tests using mixed/boundary conditions in an Amsler-type machine. Austempered ductile iron (ADI) alloyed with 1 wt.% chromium, or Carbidic ADI, was tested for comparison. For the as cast conditions, the niobium addition resulted in an increase of wear resistance owing to the low contact pressure of these tests. However, for the austempered specimens, the best performance was found for unalloyed ADI. The main factor acting in the initiation and propagation of cracks in ductile iron is the presence of the graphite nodules. The coarse carbides also contributed to the initiation of cracks and spalling of the material.