TY - JOUR A1 - Hartmann, Jürgen A1 - Knopp, Kevin A1 - Shandy, Amir A1 - Winterstein, Achim A1 - Arduini, Mariacarla A1 - Hemberger, Frank A1 - Vidi, Stephan A1 - Manara, Jochen A1 - Müller, Michael T1 - Thermophysikalische Charakterisierung von Wärmedämmschichten T1 - Thermophysical characterization of thermal barrier layers JF - tm - Technisches Messen N2 - Die Effizienzsteigerung moderner Gasturbinen erfordert die stetige Anhebung der Betriebstemperatur. Die derzeitigen Brenngastemperaturen liegen mit über 1400 °C signifikant über der kritischen Temperatur der verwendeten Turbinenstähle. Zur Gewährleistung der Betriebssicherheit werden die Turbinenschaufeln neben Aktivkühlung durch Beschichtung mit thermischen Schutzschichten, sogenannten thermal barrier coatings (TBC), geschützt. Da es sich bei den TBC um Keramikschichten handelt, ist für die Erhöhung der Haftfestigkeit das Aufbringen eines Haftvermittlers (Verbindungsschicht) notwendig. Da die Eigenschaften dünner Schichten stark von den Eigenschaften des Bulkmaterials abweichen können und zudem von der Herstellungsmethode beeinflusst werden, ist eine Untersuchung der thermischen und infrarot-optischen Eigenschaften der tatsächlichen Schichtstrukturen unumgänglich, insbesondere im Hochtemperaturbereich. Hierfür wurden Proben des reinen Trägerstahls, des Trägerstahls mit Haftvermittlerschicht und des kompletten Schichtsystems aus Trägerstahl, Haftvermittlerschicht und Wärmedämmschicht verschiedener Dicken hergestellt und mittels Laser-Flash-Methode untersucht. Die Auswertung erfolgte dabei analytisch, ausgehend von der Trägerstahl-Einschichtprobe, über die Zweischicht- und Dreischichtsysteme. Vervollständigt wurden diese Untersuchungen durch infrarot-optische Charakterisierungen, mit denen sich die Wärmeausbreitung durch die Schichtsysteme beschreiben lässt. Zusammen mit den Laser-Flash Messungen erlaubt dies eine spätere Quantifizierung der einzelnen, bei Keramiken auftretenden, Wärmetransportmechanismen. N2 - Increasing the efficiency of modern gas turbines requires the increase of operating temperature. Current fuel gas temperatures above 1400 °C significantly exceed critical temperatures of the turbine steels used. To ensure operational safety, the turbine blades are actively cooled and also protected by protective layers, the so-called thermal barrier coatings (TBC). Since the TBC are ceramic layers, an adhesion promoter (bond coat) must be applied to increase the adhesive strength. Since properties of thin layers can differ from properties of the bulk material and are also influenced by the manufacturing method, an investigation of the thermal and infrared-optical properties of the actual layer is essential, especially in the high temperature range. For this purpose, samples of the pure carrier steel, the carrier steel with bond coat and the complete layer system of carrier steel, bond coat and TBC of various thicknesses were produced and examined using the laser flash method. The evaluation was carried out analytically, starting from the single-layer sample, via the two-layer and three-layer systems. These investigations were completed by infrared-optical characterizations, allowing the description of the heat transport through the layer systems. These measurements allow a future quantification of the individual heat transport mechanisms occurring in ceramics. KW - kontaktlose Messung KW - thermische Charakterisierung KW - thermische Wärmeschutzbarrieren KW - Kontaktwiderstand KW - Laser-Flash-Verfahren KW - Contactless measurement KW - thermal characterization KW - thermal barrier coatings KW - contact resistance KW - laser flash method Y1 - 2021 U6 - https://doi.org/10.1515/teme-2021-0074 VL - 88 IS - 12 PB - Oldenbourg Wissenschaftsverlag ER - TY - JOUR A1 - Ochs, Dennis A1 - Wehnert, Kira-Kristin A1 - Hartmann, Jürgen A1 - Schiffler, Andreas A1 - Schmitt, Jan T1 - Sustainable Aspects of a Metal Printing Process Chain with Laser Powder Bed Fusion (LPBF) JF - Procedia CIRP N2 - Production companies are getting more and more aware of the relevancy of energy costs and the environmental impact of their manufactured products. Hence, the knowledge about the energy intensity of new process technologies as metal printing becomes increasingly crucial. Therefore, data about the energy intensity of entire process chains allow a detailed assessment of the life cycle costs and environmental impact of metal printed parts. As metal printing with Laser Powder Bed Fusion (LPBF) is applied from rapid prototyping to serial manufacturing processes more and more, sustainability data are useful to support a valid scale-up scenario and energetic improvements of the 3D-printing machinery as well as peripheral aggregates used in the process chain. The contribution aims to increase the transparency of the LPBF process chain in terms of its energy consumption. Therefore a generalized model to assess sustainability aspects of metal printed parts is derived. For this purpose, the LPBF process chain with the essential pre-, main- and post-processes is evaluated regarding its energy intensity. Here, the sub-processes, for example wet and dry cleaning of the printer, sieving of the metal powder or sand-blasting of the part are analyzed as well as the main printing process. Based on the derived experimental data from an installed, industry-like process chain, a model is created, which tends to generalize the experimental findings to evaluate other metal printed parts and process chain variants in terms of their energy intensity. Y1 - 2021 UR - 10.1016/j.procir.2021.01.163 VL - 98 SP - 613 EP - 618 PB - Elsevir ER - TY - JOUR A1 - Jürgen, Hartmann A1 - Arduini, Mariacarla A1 - Manara, Jochen A1 - Stark, Thomas A1 - Ebert, Hans-Peter T1 - Development and Evaluation of an Improved Apparatus for Measuring the Emissivity at High Temperatures JF - Sensors N2 - An improved apparatus for measuring the spectral directional emissivity in the wavelength range between 1 µm and 20 µm at temperatures up to 2400 K is presented in this paper. As a heating unit an inductor is used to warm up the specimen, as well as the blackbody reference to the specified temperatures. The heating unit is placed in a double-walled vacuum vessel. A defined temperature, as well as a homogenous temperature distribution of the whole surrounding is ensured by a heat transfer fluid flowing through the gap of the double-walled vessel. Additionally, the surrounding is coated with a high-emitting paint and serves as blackbody-like surrounding to ensure defined boundary conditions. For measuring the spectral directional emissivity at different emission angles, a movable mirror is installed in front of the specimen, which can be adjusted by a rotatable arrangement guiding the emitted radiation into the attached FTIR-spectrometer. The setup of the emissivity measurement apparatus (EMMA) and the measurement procedure are introduced, and the derived measurement results are presented. For evaluating the apparatus, measurements were performed on different materials. The determined emissivities agree well with values published in literature within the derived relative uncertainties below 4% for most wavelengths. KW - emissivity KW - reflectivity KW - infrared radiation KW - high temperature KW - Temperatur KW - Emissivität Y1 - 2021 UR - https://www.mdpi.com/1424-8220/21/18/6252 U6 - https://doi.org/10.3390/s21186252 SN - 1424-8220 VL - 21 IS - 18 ER - TY - JOUR A1 - Wehnert, Kira-Kristin A1 - Ochs, Dennis A1 - Schmitt, Jan A1 - Hartmann, Jürgen A1 - Schiffler, Andreas T1 - Reducing Lifecycle Costs due to Profile Scanning of the Powder Bed in Metal Printing JF - Procedia CIRP 98 N2 - First time right is one major goal in powder based 3D metal printing. Reaching this goal is driven by reducing life cycle costs for quality measures, to minimize scrap rate and to increase productivity under optimal resource efficiency. Therefore, monitoring the state of the powder bed for each printed layer is state of the art in selective laser melting. In the most modern approaches the quality monitoring is done by computer vision systems working with an interference on trained neural networks with images taken after exposure and after recoating. There are two drawbacks of this monitoring method: First, the sensor signals - the image of the powder bed - give no direct height information. Second, the application of this method needs to be trained and labeled with reference images for several cases. The novel approach presented in this paper uses a laser line scanner attached to the recoating machine. With this new concept, a direct threshold measure can be applied during the recoating process to detect deviations in height level without prior knowledge. The evaluation can be done online during recoating and feedback to the controller to monitor each individual layer. Hence, in case of deviations the location in the printing plane is an inherent measurement and will be used to decide which severity of error is reported. The signal is used to control the process, either by starting the recoating process again or stopping the printing process. With this approach, the sources of error for each layer can be evaluated with deep information to evaluate the cause of the error. This allows a reduction of failure in the future, which saves material costs, reduces running time of the machine life cycle phase in serial production and results in less rework for manufactured parts. Also a shorter throughput time per print job results, which means that the employee can spent more time to other print jobs and making efficient use of the employee’s work force. In summary, this novel approach will not only reduce material costs but also operating costs and thus optimize the entire life cycle cost structure. The paper presents a first feasibility and application of the described approach for test workpieces in comparison to conventional monitoring systems on an EOS M290 machine. Y1 - 2021 UR - 10.1016/j.procir.2021.01.175 VL - 98 SP - 684 EP - 689 PB - Elsevir ER -