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Eingeladener Vortrag
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Metalle
(2019)
Dieses Standardwerk bietet eine Darstellung der Struktur und Eigenschaften der Metalle und ihrer Anwendungen als Werkstoffe. Im ersten, wissenschaftlichen Teil werden der atomare und mikroskopische Aufbau, die thermodynamischen und die grundlegenden physikalischen und mechanischen Eigenschaften der Metalle beschrieben sowie die Grundlagen der thermisch aktivierten Reaktionen und der Phasenumwandlungen. Die wichtigsten experimentellen Untersuchungsmethoden werden erläutert, wobei die mikroskopischen und Beugungsverfahren einen Schwerpunkt bilden.
Im zweiten, technischen Teil werden die Werkstoffgruppen der Metalle und ihre anwendungsbezogenen Eigenschaften behandelt. Dabei wird auf die zugrunde liegenden Legierungen und die Verfahren zur gezielten Einstellung ihrer Eigenschaften eingegangen. Schwerpunkte bei der Darstellung der Werkstoffe sind die Stähle, die teilchengehärteten Legierungen, die Magnetwerkstoffe und die pulvermetallurgisch hergestellten Werkstoffe. Außerdem werden die Oberflächeneigenschaften und die Verfahren zur Oberflächenbehandlung dargestellt.
The age hardening response of a high-purity Al–4Cu–1Li–0.25Mn alloy (wt. %) during isothermal aging without and with an applied external load was investigated. Plate shaped nanometer size T1 (Al2CuLi) and θ′ (Al2Cu) hardening phases were formed. The precipitates were analyzed with respect to the development of their structure, size, number density, volume fraction and associated transformation strains by conducting transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) studies in combination with geometrical Phase analysis (GPA). Special attention was paid to the thickening of T1 phase. Two elementary types of single-layer T1 precipitate, one with a Li-rich (Type 1) and another with an Al-rich (Defect Type 1) central layer, were identified. The results show that the Defect Type 1 structure can act as a precursor for the Type 1 structure. The thickening of T1 precipitates occurs by alternative stacking of These two elementary structures. The thickening mechanism was analyzed based on the magnitude of strain associated with the precipitation transformation normal to its habit plane. Long-term aging and aging under load resulted in thicker and structurally defected T1 precipitates. Several types of defected precipitates were characterized and discussed. For θ′ precipitates, a ledge mechanism of
thickening was observed. Compared to the normal aging, an external load applied to the peak aged state leads to small variations in the average sizes and volume fractions of the precipitates.
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.
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.
The current competitive situation on electricity markets forces power plants into cyclic operation regimes with frequent load shifts and starts/shutdowns. In the present work, the cyclic mechanical behavior of ferritic-martensitic 9-12 % Cr steels under isothermal and thermomechanical loading was investigated for the example of grade P92 material. A continuous softening was observed under all loading conditions. The introduction of hold periods to the applied cycles reduced material lifetime, with most prominent effects at technologically relevant small strain levels. The microstructural characterization reveals a coarsening of the original “martensitic” lath-type microstructure to a structure with polygonal subgrains and reduced dislocation density. The microstructural data forms the input for a physically-based modelling approach, both of which are presented in “Part 2: Microstructural Evolution during Cyclic Loading and its Representation in a Physically-based Micromechanical Model“.
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.
To accelerate the growth of Industry 4.0 technologies, the digitalization of mechanical testing laboratories as one of the main data-driven units of materials processing industries is introduced in this paper. The digital lab infrastructure consists of highly detailed and standard-compliant materials testing knowledge graphs for a wide range of mechanical testing processes, as well as some tools that enable the efficient ontology development and conversion of heterogeneous materials’ mechanical testing data to the machine-readable data of uniform and standardized structures. As a basis for designing such a digital lab, the mechanical testing ontology (MTO) was developed based on the ISO 23718 and ISO/IEC 21838-2 standards for the semantic representation of the mechanical testing experiments, quantities, artifacts, and report data. The trial digitalization of materials mechanical testing lab was successfully performed by utilizing the developed tools and knowledge graph of processes for converting the various experimental test data of heterogeneous structures, languages, and formats to standardized Resource Description Framework (RDF) data formats. The concepts of data storage and data sharing in data spaces were also introduced and SPARQL queries were utilized to evaluate how the introduced approach can result in the data retrieval and response to the competency questions. The proposed digital materials mechanical testing lab approach allows the industries to access lots of trustworthy and traceable mechanical testing data of other academic and industrial organizations, and subsequently organize various data-driven research for their faster and cheaper product development leading to a higher performance of products in engineering and ecological aspects.
The current competitive situation on electricity markets forces power plants into cyclic operation regimes with frequent load shifts and starts/shutdowns. In the present work, the cyclic mechanical behavior of ferritic-martensitic 9-12 % Cr steels under isothermal and thermomechanical loading was investigated for the example of grade P92 material. A continuous softening was observed under all loading conditions. The introduction of hold periods to the applied cycles reduced material lifetime, with most prominent effects at technologically relevant small strain levels. The microstructural characterization reveals a coarsening of the original “martensitic” lath-type microstructure to a structure with polygonal subgrains and reduced dislocation density. The microstructural data forms the input for a physically-based modelling approach.
Die Bereitstellung von zuverlässigen Werkstoffdaten stand für die Werkstoffprüfung seit dem 19. Jahrhundert in zentraler Stelle. Mit der zunehmender Digitalisierung unserer Gesellschaft gewinnt das Datenmanagement insbesondere im Hinblick auf die Modellierungs- und Simulationsaktivitäten an Bedeutung.
In unserem Beitrag beschreiben wir die gegenwärtigen Aktivitäten in Deutschland – insbesondere die NFDI-MatWerk und die BMBF-Initiative MaterialDigital – sowie in Europa und Übersee. Abschließend heben wir die Auswirkungen auf die technische und akademische Aus- und Weiterbildung.
Die hohen Betriebstemperaturen während des Einsatzes von Radialverdichterrädern in Abgasturboladern führen zu einer Änderung der ursprünglich eingestellten Mikrostruktur in der warmfesten Aluminiumlegierung EN AW-2618A (Überalterung). Grund dafür sind thermische Belastungen, die nahe der Aushärtetemperatur liegen und diese kurzzeitig sogar überschreiten können. Die Alterungsmechanismen wurden zusammen mit den Themen niederzyklische (LCF) und thermomechanische Ermüdung (TMF) sowie Kriechen bis max. 190 °C in vorangegangenen Forschungsvorhaben untersucht. Kaum untersucht war bisher das Verhalten der Legierung unter hochzyklischer Beanspruchung (HCF) sowie der Einfluss von Kerben und Lastkollektiven. Da zukünftig mit weiter steigenden Betriebstemperaturen für Radialverdichter zu rechnen ist, wurde in diesem Forschungsvorhaben das HCF-Verhalten bei 230 °C untersucht und somit bei einer Prüftemperatur, die deutlich oberhalb der Aushärtetemperatur liegt. Das Ziel des Projektes war der Aufbau einer geeigneten experimentellen Datenbasis, das Verständnis der relevanten mikrostrukturellen Prozesse sowie die Weiterentwicklung und Anpassung geeigneter Modelle und Bewertungsmethoden.
Das experimentelle Untersuchungsprogramm umfasste neben einer Basischarakterisierung des HCF-Verhaltens am Ausgangszustand T61 gezielte mechanische Versuche zur Isolierung der Einflussfakto-ren Mittelspannung (𝑅 = −1, 𝑅 = 0,1), Werkstoffüberalterung (T61, 10 h/230 °C, 1000 h/230 °C), Prüftemperatur (20 °C, 230 °C), Prüffrequenz (0,2 Hz, 20 Hz) sowie Kerbwirkung und variable Amplituden. Darauf aufbauend wurden die in den vorangegangenen Projekten entwickelten Modelle und Bewertungsmethoden angepasst und weiterentwickelt, um die genannten thermischen und mechanischen Belastungen in der Lebensdauerbewertung abzubilden.
The high operating temperatures of radial compressor wheels in exhaust gas turbochargers lead to a change in the original microstructure of the heat-resistant aluminum alloy EN AW-2618A (overaging). This is caused by thermal loads that are close to the age hardening temperature and can even exceed it for a short time. The aging mechanisms have been investigated together with low cycle fatigue (LCF), thermomechanical fatigue (TMF) and creep up to max. 190 °C in previous research projects. The be-havior of the alloy under high cycle fatigue (HCF) and the influence of load spectra have hardly been investigated. Since the operating temperatures of centrifugal compressors are expected to increase in the future, this research project investigated the HCF behavior at 230 °C, a test temperature significantly higher than the age hardening temperature. The objectives of the project were to establish a suitable experimental database, to understand the relevant microstructural processes, and to further develop and adapt suitable models and evaluation methods.
In addition to a basic characterization of the HCF behavior in the initial condition T61, the experimental investigation program included targeted mechanical tests to isolate the influencing factors of mean stress (𝑅=−1, 𝑅=0.1), material overaging (T61, 10 h/230 °C, 1000 h/230 °C), test temperature (20 °C, 230 °C), test frequency (0.2 Hz, 20 Hz) as well as variable amplitudes. On this basis, the models and evaluation methods developed in the previous projects were adapted and further developed to reflect thermal and mechanical loads in the lifetime assessment.
The elastic properties (Young's modulus, shear modulus) of Ni-based alloy Inconel IN718 were investigated between room temperature and 800 °C in an additively manufactured variant (laser powder bed fusion, PBF‑LB/M) and from a conventional process route (hot rolled bar). The moduli were determined using the dynamic resonance method. The data set includes information on processing parameters, heat treatments, grain size, specimen dimensions and weight, Young’s and shear modulus as well as their measurement uncertainty.
The dataset was generated in an accredited testing lab using calibrated measuring equipment. The calibrations meet the requirements of the test procedure and are metrologically traceable. The dataset was audited as BAM reference data.
The elastic properties (Young's modulus, shear modulus) of austenitic stainless steel AISI 316L were investigated between room temperature and 900 °C in an additively manufactured variant (laser powder bed fusion, PBF‑LB/M) and from a conventional process route (hot rolled sheet). The moduli were determined using the dynamic resonance method. The data set includes information on processing parameters, heat treatments, grain size, specimen dimensions and weight, Young’s and shear modulus as well as their measurement uncertainty.
The dataset was generated in an accredited testing lab using calibrated measuring equipment. The calibrations meet the requirements of the test procedure and are metrologically traceable. The dataset was audited as BAM reference data.
This article reports temperature-dependent elastic properties (Young’s modulus, shear modulus) of three alloys measured by the dynamic resonance method. The alloys Ti-6Al-4V, Inconel IN718, and AISI 316 L were each investigated in a variant produced by an additive manufacturing processing route and by a conventional manufacturing processing route. The datasets include information on processing routes and parameters, heat treatments, grain size, specimen dimensions, and weight, as well as Young’s and shear modulus along with their measurement uncertainty. The process routes and methods are described in detail. The datasets were generated in an accredited testing lab, audited as BAM reference data, and are hosted in the open data repository Zenodo. Possible data usages include the verification of the correctness of the test setup via Young’s modulus comparison in low-cycle fatigue (LCF) or thermo-mechanical fatigue (TMF) testing campaigns, the design auf VHCF specimens and the use as input data for simulation purposes.
The elastic properties (Young's modulus, shear modulus) of titanium alloy Ti-6Al-4V were investigated between room temperature and 400 °C in an additively manufactured variant (laser-based directed energy deposition with powder as feedstock, DED-LB/M) and from a conventional process route (hot rolled bar). The moduli were determined using the dynamic resonance method. The data set includes information on processing parameters, heat treatments, microstructure, grain size, specimen dimensions and weight, Young’s and shear modulus as well as their measurement uncertainty.
The dataset was generated in an accredited testing lab using calibrated measuring equipment. The calibrations meet the requirements of the test procedure and are metrologically traceable. The dataset was audited as BAM reference data.
The influence of prestraining on the aging response of an Al-Cu-Li alloy is investigated by preparation of different strain states (3 %, 4 %, 6 %) of the initial aging state. The Brinell hardness of the subsequently aged samples (up to 60 h aging time) was measured and it was found that the increasing dislocation concentration in the 3 different initial states leads to faster hardness increases and slightly higher maximum hardness.
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.
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.