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Eingeladener Vortrag
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Oxidation of a single crystal nickel-base superalloy at 950 °C - a kinetic and microstructure study
(2008)
The nickel-base single crystal alloy investigated is a widely used material for first and second row blades in stationary gas turbines. Nickel-base superalloys are especially designed to resist high temperature oxidation by process gases. To determine this high temperature behaviour oxidation testing was carried out using samples cut perpendicular to (001)-direction. Microstructures were characterized by X-ray diffraction XRD, Light Microscopy LM, Scanning Electron Microscopy SEM, and X-ray energy dispersive spectroscopy (EDS), after a series of heat treatments (950 °C, 0 h - 1000 h). Mass gain and the respective thicknesses of the different oxide layers were measured to determine oxidation kinetics. In general, the isothermal oxidation behaviour at 950 °C, as defined by weight gain, follows a parabolic law with a parabolic rate constant around 1.4 · 10-2 mg2/(cm4 · h). A short incubation time is followed by the constitution of a multi-layered oxide scale. The oxide scale consists of a three layer structure. An outer scale contains a Ti-bearing thin film associated as TiO2 and NiTiO3 but mostly Cr attributed to Cr2O3, (Ni/Co)Cr2O4 beside NiTaO4. This outer scale is connected to a discontinuous layer of inner oxidation consisting mainly of Al2O3, which is followed by an area of γ´-depletion within the base material.
CO2-corrosion of injection pipe steels is a relevant safety issue when emission gasses are compressed in deep geological layers (CCS). The reliability of the steels used at the geological onshore CCS-site at Ketzin, Germany, is demonstrated in laboratory experiments under an equivalent corrosive environment (T=60 °C,p=1-60 bar, aquifer water, CO2-flow rate of 3 l/h, 700 h8000 h heat treatment). Corrosion kinetics and microstructures were characterized using samples of the heat treated steel 1.7225 (AISI 4140, 42CrMo4) used for casing, and samples of the martensitic stainless injection-pipe steel 1.4034 (AISI 420, X46Cr13).
During carbon capture and storage (CCS) CO2-corrosion of pipe steels is a relevant safety issue when emission gasses are compressed in deep geological layers. The reliability of the steels 42CrMo4, X20Cr13, X46Cr13 and X35CrMo17 is demonstrated in long term laboratory experiments up to 2 years of exposure time. Testings were carried out at ambient pressure under an equivalent corrosive environment as found at the geological onshore CCS-site at Ketzin, Germany (T=60 °C, aquifer water).
Properties of pipe steels for CCS (carbon capture and storage) technology require resistance against the corrosive environment of a potential CCS-site (heat, pressure, salinity of the aquifer, CO2-partial pressure). The influence of austenitzing in heat treatment routines of two different injection pipe Steels (1.4034, X46Cr13 and 1.4021, X20Cr13) was evaluated. Steel coupons were austenitized at different temperatures (900- 1050 °C) for different lengths of time (30-90 min) before quenching and annealing prior to long term corrosion experiments (60°C, 100 bar, artificial brine close to a CCS-site in the Northern German Basin, Germany). In general, fewer pits are found on X46Cr13. Comparing steels with 13% chromium each the higher carbon content of X46Cr13 (0.46% C) results in a lower number of pits compared to X20Cr13 (0.20% C). It is found that neither the carbon content of the steels nor austenitizing temperature has much influence, but local corrosion behaviour is most susceptible towards austenitzing time.
Properties of pipe steels for CCS (carbon capture and storage) technology require resistance against the corrosive environment of a potential CCS-site (heat, pressure, salinity of the aquifer, CO2-partial pressure). The influence of austenitzing in heat treatment routines of two different injection pipe steels (1.4034, X46Cr13 and 1.4021, X20Cr13) was evaluated. Steel coupons were austenitized at different temperatures (900-1050 °C) for different lengths of time (30-90 min) before quenching and annealing prior to long term corrosion experiments (60°C, 100 bar, artificial brine close to a CCS-site in the Northern German Basin, Germany). In general, fewer pits are found on X46Cr13. Comparing steels with 13% chromium each the higher carbon content of X46Cr13 (0.46% C) results in a lower number of pits compared to X20Cr13 (0.20% C). It is found that neither the carbon content of the steels nor austenitizing temperature has much influence, but local corrosion behaviour is most susceptible towards austenitzing time.
Proben unterschiedlich wärmebehandelter, hochlegierter, rostfreier Stahlqualitäten, die potenziell als Injektionsrohr-Stähle eingesetzt werden können - AISI 420 X46Cr13, AISI 420J X20Cr13 und AISI 630 X5CrNICuNb16-4 - wurden bei 60 °C sowohl bei Normaldruck als auch bei 100 bar für 700 bis 8.000 Stunden in einem C02-gesättigtem, synthetisch hergestellten Laboraquiferwasser ausgelagert. Dieses Laboraquiferwasser entspricht der erwarteten Zusammensetzung des Aquiferwassers des norddeutschen Beckens, in das im CCS- Versuchsfeld von Ketzin (CCS Carbon Capture and Storage) über zwei Jahre hinweg technisch reines C02 injiziert wurde. Die Korrosionsraten und Schichtwachstumsraten auf den Stählen sind am niedrigsten für Stähle, die vor der Langzeitauslagerung gehärtet und anschließend zwischen 600 °C und 670 °C angelassen wurden. Lokale Korrosion (Lochfraß) zeigt sich in Form von kleinsten Löchern auf der Stahloberfläche. Der Durchmesser dieser Löcher nimmt mit steigendem Kohlenstoffgehalt des Stahls ab. Gleichzeitig nimmt die Anzahl der gezählten Löcher auf der Oberfläche zu. Insgesamt wird festgestellt, dass Stähle mit einer martensitischen Gefügestruktur in dieser nachempfundenen CCS-Atmosphäre die beste Korrosionsbeständigkeit gegenüber dem C02-gesättigten, salinen Aquifer bietet.
Properties of pipe steels for CCS (carbon capture and storage) technology require resistance against the corrosive environment of a potential CCS-site (heat, pressure, salinity of the aquifer, CO2-partial pressure). The influence of austenitzing in heat treatment routines of two different injection pipe steels (1.4034, X46Cr13 and 1.4021, X20Cr13) was evaluated. Steel coupons were austenitized at different temperatures (900- 1050 °C) for different lengths of time (30-90 min) before quenching and annealing prior to long term corrosion experiments (60°C, 100 bar, artificial brine close to a CCS-site in the Northern German Basin, Germany). In general, fewer pits are found on X46Cr13. Comparing steels with 13% chromium each the higher carbon content of X46Cr13 (0.46% C) results in a lower number of pits compared to X20Cr13 (0.20% C). It is found that neither the carbon content of the steels nor austenitizing temperature has much influence, but local corrosion behaviour is most susceptible towards austenitzing time.
Potential of martensitic stainless steel X5CrNiCuNb 16-4 as pipe steel in corrosive CCS environment
(2017)
Pipe steels suitable for carbon capture and storage technology (CCS) require resistance against the corrosive environment of a potential CCS-site (heat, pressure, salinity of the aquifer, CO2-partial pressure). X5CrNiCuNb16-4 has been proven to be sufficient resistant in corrosive environments, but shows rather unusual corrosion behaviour in CCS environment. Therefore differently heat treated coupons of 1.4542 were kept at T=60 °C and ambient pressure as well as p=100 bar for 700 h - 8000 h in an a) water saturated supercritical CO2 and b) CO2-saturated synthetic aquifer environment similar to on-shore CCS-sites in the Northern German Basin. Additionally fatigue tests were performed via push-pull tests with a series of 30 specimens was tested at stress amplitudes between 150 MPa and 500 MPa (sinusoidal dynamic test loads, R=-1; resonant frequency ~ 30 Hz). Best corrosion resistance in the liquid phase is achieved via normalizing prior to exposure and hardening+tempering at 670 °C leads to lowest corrosion rates in the supercritical phase. With no regard to atmosphere discontinuously ellipsoidal surface corrosion regions appear after exposure of 4000 h and more. The endurance limit of X5CrNiCuNb16-4 measured in air is reduced by more than 50% when exposed to CCS environment (maximum number of cycles (10 x 106) at a stress amplitude of 150 MPa) The scatter range TN = 1:34 is disproportionately large contributing to an overall unusual corrosion behaviour.
Pipe steels suitable for carbon capture and storage technology (CCS) require resistance against the corrosive environment of a potential CCS-site, e.g. heat, pressure, salinity of the aquifer, CO2-partial pressure. Samples of different mild and high alloyed stainless injection-pipe steels partially heat treated: 42CrMo4, X20Cr13, X46Cr13, X35CrMo4 as well as X5CrNiCuNb16-4 were kept at T=60 °C and ambient pressure as well as p=100 bar for 700 h - 8000 h in a CO2-saturated synthetic aquifer environment similar to possible geological on-shore CCS-sites in the northern German Basin. Main corrosion products are FeCO3 and FeOOH. Corrosion rates obtained at 100 bar are generally much lower than those measured at ambient pressure. Highest surface corrosion rates are 0.8 mm/year for 42CrMo4 and lowest 0.01 mm/year for X5CrNiCuNb16-4 in the vapour phase at ambient pressure. At 100 bar the highest corrosion rates are 0.01 mm/year for 42CrMo4, X20Cr13 (liquid phase), X46Cr13 and less than 0.01 mm/year for X35CrMo4 and X5CrNiCuNb16-4 after 8000 h of exposure with no regard to atmosphere. Martensitic microstructure offers good corrosion resistance.
Carbon Capture and Storage (CCS) is well acknowledged to mitigate climate change. Therefore, pipe Steels suitable for CCS technology require resistance against the corrosive environment of a potential CCS-site, e.g. heat, pressure, salinity of the aquifer, CO2-partial pressure. Samples of different mild and high alloyed stainless injection-pipe Steels partially heat treated: 42CrMo4, X20Cr13, X46Cr13, X35CrMo4 as well as X5CrNiCuNb16-4 were kept at T=60 °C and ambient pressure as well as p=100 bar for 700 h - 8000 h in a CO2-saturated synthetic aquifer environment similar to possible geological on-shore CCS-sites in the northern German Basin. Main corrosion products analysed on pits are FeCO3 and FeOOH. The carbon content does not show significant influence on the pitting behaviour. Generally, higher chromium Content results in better corrosion resistance. Although X35CrMo17-1 and X5CrNiCuNb16-4 show low surface corrosion rates, their resistance against local corrosion in CCS environment is not significantly better compared to the much less costly Steels X20Cr13 and X46Cr13.
Immersion tests of potential injection pipe steels 42CrMo4, X20Cr13, X46Cr13, X35CrMo4 and X5CrNiCuNb16-4 at T=60 °C and ambient pressure and p=100 bar were performed for 700 h - 8000 h in a CO₂-saturated synthetic aquifer environment similar to CCS-sites in the Northern-German-Basin. Main corrosion products are FeCO₃ and FeOOH. Highest surface corrosion rates at ambient pressure are 0.8 mm/year for 42CrMo4 and lowest 0.01 mm/year for X5CrNiCuNb16-4. Corrosion rates at 100 bar (max. 0.01 mm/year for 42CrMo4, X20Cr13, X46Cr13) are generally lower than at ambient pressure (<0.01 mm/year for X35CrMo4, X5CrNiCuNb16-4). Heat treatment to martensitic microstructure offers good corrosion resistance.
The oxidation behaviour of single crystal PWA 1483 at 950 °C was investigated by means of XRD, SEM and EDS. The parabolic oxidation behaviour, as defined by mass gain and the respective oxide layer thicknesses, is characterized by a parabolic rate constant of about 4 × 10-6 mg²/(cm4 × s) and the formation of a multi-layered oxide scale. An outer scale contains a Ti-bearing thin film composed of TiO2 and NiTiO3 but mostly Cr in Cr2O3 and (Ni/Co)Cr2O4 besides NiTaO4. This outer scale is connected to a discontinuous layer of Al2O3 and an area of γ?'-depletion within the base material.
In engineering storage sites for Carbon Sequestration the CO2-induced corrosion of injection pipe steels is a relevant safety issue when emission gasses are compressed in deep geological layers. The reliability of the steels suitable for the geological onshore CCS-site (Carbon Capture and Storage) at Ketzin, Germany, is demonstrated in laboratory experiments in equivalent corrosive environment (T = 60 °C, p = 160 bar, aquifer water, CO2-flow rate of 3 L/h, 7008000 h exposure time). Corrosion kinetics and microstructures were characterized using specimens of the heat treated steel 42CrMo4 (1.7225) used for casing, and specimens of the martensitic stainless injection-pipe steel X46Cr13 (1.4034).
Supercritical CO2-corrosion in heat treated pipe steels during carbon capture and storage CCS
(2012)
Predicting the life time of steels in CCS environment from long term local corrosion experiments
(2012)
Oxidation of a single crystal Nickel-Base Superalloy at 950°C - a kinetik and microstructure study
(2008)
Isothermal oxidation behavior and microstructure of the single crystal superalloy PWA 1483 at 950 C
(2008)
High-Temperatur-High Pressure Stress-Strain Testing of Materials in CO2-Containing Saline Solutions
(2015)
First year students especially with migration background and language deficiencies rate material science in mechanical engineering as one of the fundamental courses with high work load and necessity of language skills due to the descriptive nature of the course. Therefore a blended learning course structure using based on inverted classroom teaching scenarios was established. Heart of the self-study period are visualizing peer-to-peer lecture films supported by micro-lectures along with various online teaching materials. Although students with migration background generally scored lower in tests due to the lack of language skills improved learning outcomes are demonstrated in high quality class discussions and in overall understanding. This paper introduces the learning structure and graded activities, evaluates the course and compares results of native German-speaking students to those of students with migration background.
Mit Beginn der Covid-19 Pandemie und dem damit verbundenen ausschließlichen Lehren im online-Format war die Hoffnung verbunden ein Blended Learning Lehrformat für die Studieeingangsphase ohne viel konzeptionelle Änderungen übertragen zu können. Der Kurs Werkstofftechnik als Grundlagenfach für den Maschinenbau baut sich auf inverted classroom Lehrszenarien auf, deren Lerngrundlage hierfür eigens produzierte und auf das Lernziel abgestimmte Lehrfilme und Lightboard-Vorlesungen darstellen. Im Kontext der Studieneingangsphase bieten audiovisuell stimulierende Lehrfilme umfassende Lernmedien, wenn sie analog der Lerninhalte einem technischen und didaktischen Qualitätsanspruch genügen. In der Praxis des SS2020 und WS2020/21 hat sich gezeigt, dass die Moderation und Durchführung eines online-Kurses sich deutlich von dem eins blended learning-Kurses unterscheidet. Um denselben Lernerfolg bei Studierenden zu erzielen, müs-sen Anforderungen viel genauer und detaillierter verfasst werden, Studierende enger und persönlicher begleitet werden und Lehrfilme und Lernmedien in einen Gesamtzusammenhang gestellt werden. Im Folgenden werden aus persönlicher Erfahrung heraus niederschwellige, zum Teil ungewöhnliche praktische Erfahrungen zur erfolgreichen Umsetzung von Lehrfilm-basierten inverted classroom Lehrszenarien zusammengefasst und im Hinblick auf die online-Lehre bewertet.
Flipping the classroom is a method to let students study on their own and then take time to discuss their questions and do extended hands-on lectures or exercises in class – or in the case of the covid-19 pandemic during plenary online sessions. First year mechanical engineering students use different teaching materials (mainly lecture videos, lightboard videos and micromodule lectures) to study from a distance and comprehend the principle underlying science in theory. Then the online plenary lectures offer the opportunity to apply their knowledge and transfer different scientific aspects of the course to get the bigger picture. Exercises, worked solutions, selfassessed tests and peer-instruction during present time help students to check on their learning progress. However, the self-study periods and (online) plenary sessions need to be guided carefully. To meet the course learning outcome and overcome the diversity of a first year class various practical leads have to be fulfilled to turn flipped classroom teaching into success.
Crack growth tests have been performed at 950 °C with Single Edge Notch specimens of the Ni-based single crystal superalloy PWA1483. In particular, several orientations and frequencies have been investigated, thus allowing the assessment of the influence of these parameters on the crack growth rate. In addition, oxidation experiments have been carried out to characterize the kinetics of the outer oxide scale growth at the same temperature.
On the other side, crack growth has been simulated with the Finite Element program ABAQUS in real test conditions by the node release technique. The nodes are released according to the measured crack growth rate.
The simulation results are compared with the test results on the basis of the computed Crack Tip Opening Displacement (CTOD). For this purpose, the crack is propagated until a stabilized value of the CTOD is obtained. This is usually the case when the crack has crossed the initial plastic zone. The procedure provides an evaluation of the effects of cycle frequency, crystal orientation, plasticity and oxide induced crack closure.