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- Microstructure (16) (entfernen)
Organisationseinheit der BAM
- 5 Werkstofftechnik (7)
- 5.2 Metallische Hochtemperaturwerkstoffe (7)
- 9 Komponentensicherheit (3)
- 5.1 Mikrostruktur Design und Degradation (2)
- 5.5 Materialmodellierung (2)
- 8 Zerstörungsfreie Prüfung (1)
- 8.5 Röntgenbildgebung (1)
- 9.3 Schweißtechnische Fertigungsverfahren (1)
- 9.4 Integrität von Schweißverbindungen (1)
- 9.6 Additive Fertigung metallischer Komponenten (1)
Eingeladener Vortrag
- nein (2)
The uniaxial, torsional and axial-torsional thermomechanical fatigue (TMF) behavior of the near-γ TiAl-alloy TNB-V5 was investigated. TMF tests were performed at 400-800 °C with mechanical strain amplitudes ranging from 0.15% to 0.7%. The tests were conducted thermomechanically in-phase (IP) and out-of-phase (OP).
For the same lifetimes, uniaxial IP tests required the highest strain amplitudes, while OP test conditions were most damaging and needed the lowest strain amplitudes. The Mises equivalent mechanical strain amplitudes of pure torsional tests were found in between uniaxial in-phase and out-of-phase tests for the same lifetimes. The non-proportional multiaxial out-of-phase test showed a lower lifetime at the same equivalent mechanical strain amplitude compared to the other types of tests.
The microstructure has been characterized applying electron microscopy and microstructural parameters such as fraction of twinned grains, grain size, lamellar distance and dislocation density have been quantified.
In the present work, the titanium alloy Ti-6.8Mo-4.5Fe-1.5Al (Timetal LCB) was investigated with respect to the microstructural evolution during strain controlled fatigue loading. The alloy was developed to reduce the generally high material costs of β-alloys by substituting expensive beta stabilizers by using a standard Fe-Mo master alloy. One possible application seen in the automotive industry is the substitution os suspension structural parts currently made of steel, suc as suspension springs. These components require a high strength and fatigue resistance.
Aluminiumlegierungen mit besonders hoher Festigkeit werden vor allem in der Luft- und Raumfahrt sowie der Automobilindustrie eingesetzt. Ein Anwendungsbeispiel im Fahrzeugbereich sind Radialverdichterräder von Abgasturboladern. Der hierfür untersuchte Werkstoff ist die Legierung 2618A. Die hohe Festigkeit wird durch Ausscheidungshärtung erreicht. Es scheiden sich hierbei durch eine entsprechende Wärmebehandlung Al-Cu-Mg-Teilchen in die Aluminium-Matrix aus. Diese Teilchen stellen Hindernisse für die Bewegung von Versetzungen dar und haben im Fall der Legierung 2618A stabförmige Geometrie. Durch Einsatz bei Betriebstemperatur von etwa 160 °C bis 190 °C vergröbern die Teilchen im Verlauf der Einsatzzeit (Ostwaldreifung) und die Festigkeit nimmt ab.
Der Zwischenbericht soll einen Überblick über die bisherigen experimentellen und theoretischen Ergebnisse geben. Es konnten Brinell-Härteverläufe nach Auslagerung bei 160 °C, 180 °C und 190 °C bis 8.760 h Auslagerungszeit gemessen werden. Erste TEM (Transmissionselektronenmikroskopie )-Untersuchungen der Mikrostruktur liegen vor. Anhand dieser Untersuchungen wurden erste Simulationen und Berechnungen der AI-Cu-Mg-Teilchengrößenentwicklung (Vergröberung) durchgeführt. Auswirkungen dieser Vergröberung der AlCu-Mg-Teilchen auf die Fließgrenze bei Raumtemperatur wurden berechnet. Weitere Ergebnisse sind Kriechversuche an Proben im Ausgangszustand T61 der Legierung 2618A bei den Temperaturen 160 °C, 180 °C und 190 °C. Um das zyklische visko-plastische Verhalten des Werkstoffes und den Einfluss der Alterung zu untersuchen, wurden LCF-Ermüdungsversuche an verschiedenen Auslagerungszuständen durchgeführt.
The aluminium alloy 2618A is an Al-Cu-Mg alloy which is part of the 2xxx series of age-hardenable alloys. These materials are designed for long-term Operation in transportation and aerospace industries. The desired properties, e.g. creep behavior, hardness, and damage tolerance, are controlled by the distribution of fine precipitates formed within the matrix. However, the strength of the material declines du ring exposition to elevated temperatures due to the overageing of the S-phase precipitates (AI2CuMg) and the conversion of the S-phase into the stable equilibrium S-phase. A quantitative model of the overageing process at application relevant temperatures would be desirable for accurate predictions of component lifetime made from the 2618A alloy.
Experimental and phase field studies of age hardening response of a high purity Al‐4Cu‐1Li‐0.25Mn‐alloy (mass %) during isothermal aging are conducted. In the experiments, two hardening phases are identified: the tetragonal θ′ (Al₂Cu) phase and the hexagonal T1 (Al₂CuLi) phase. Both are plate shaped and of nm size. They are analyzed with respect to the development of their size, number density and volume fraction during aging by applying different analysis techniques in TEM in combination with quantitative microstructural analysis. 3D phase‐field simulations of formation and growth of θ′ phase are performed in which the full interfacial, chemical and elastic energy contributions are taken into account. 2D simulations of T1 phase are also investigated using multi‐component diffusion without elasticity. This is a first step toward a complex phase‐field study of T1 phase in the ternary alloy. The comparison between experimental and simulated data shows similar trends. The still unsaturated volume fraction indicates that the precipitates are in the growth stage and that the coarsening/ripening stage has not yet been reached.
A study was made on the effect of creep loading on the precipitate radii evolution of the aluminum alloy 2618A.
The overageing process of the alloy was investigated under load at a temperature of 190 °C with stresses between 79 and 181 MPa and compared to stress free isothermal ageing. The precipitates responsible for strength were characterized using dark-field transmission electron microscopy (DFTEM). This allows the experimental Determination of radii distributions of the rod-shaped Al2CuMg precipitates and the evaluation regarding their mean precipitate radius. It was found that the mean precipitate radius enables the comparison of the different microstructural conditions of crept and uncrept samples. The mean precipitate radii of the samples experiencing creep are significantly higher than those of undeformed samples. It was shown that the acquired radii distributions are viable to determine averaged particle radii for comparison of the aged samples. A ripening process including pipe diffusion along dislocations describes the data on coarsening very well for the creep samples.
The aluminum alloy 2618A is applied for engine components such as radial compressor wheels which operate for long time at elevated temperatures. This results in coarsening of the hardening precipitates and degradation in mechanical properties during the long-term operation, which is not taken into account in the current lifetime prediction models due to the lack of quantitative microstructural and mechanical data. To address this issue, a quantitative investigation on the evolution of precipitates during long-term aging at 190 °C for up to 25,000 h was conducted. Detailed transmission electron microscopy (TEM) was combined with Brinell hardness measurements and thorough differential scanning calorimetry (DSC) experiments. The results showthat GPB zones and S-phase Al2CuMg grow up to < 1,000 h during which the GPB zones dissolve and S-phase precipitates form. For longer aging times, only S-phase precipitates coarsen, which can be well described using the Lifshitz–Slyozov Wagner theory of ripening. A thorough understanding of the underlying microstructural processes is a prerequisite to enable the integration of aging behavior into the established lifetime models for components manufactured from alloy 2618A.
Evaluation of high spatial resolution imaging of magnetic stray fields for early damage detection
(2017)
The paper discusses the evaluation of elastic and plastic strain states in two low-carbon steels of the same steel group with high spatial resolution GMR (giant magneto resistance) sensors. The residual stress distributions of tungsten inert gas welded plates were determined by means of neutron diffraction as a reference. The normal component of local residual magnetic stray fields arise in the vicinity of the positions of maximum stress. The experiments performed on flat tensile specimen indicate that the boundaries of plastic deformations are a source of stray fields. The spatial variations of magnetic stray fields for both the weld and the tensile samples are in the order of the earths magnetic field.
Materials subjected to high-temperature service conditions will change their microstructure with time. Associated with this aging process is a change of mechanical properties as well as a change of damage mechanisms. Within the scope of the FVV project Aging and Lifetime, Fraunhofer IWM in Freiburg and BAM in Berlin (both Germany) experimentally characterized the widespread high-temperature aluminum alloy EN AW-2618A in different overaging states. Based on the experimental findings, models for numerical lifetime assessment with the finite-element method were implemented.