670 Industrielle Fertigung
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The Life Cycle Assessment (LCA) approach is the most important tool in the evaluation of environmental (sustainability) impacts of products and processes. We used the method to conduct an impact analysis with regard to raw material inputs (pulp) for the German paper production industry. In our analysis, we compare the environmental effects of primary sulphate pulp, scrap paper pulp and grass-based pulp and estimate their impacts in the impact categories "greenhouse gas emissions", "eutrophication" as well as "energy and water consumption". Furthermore, we discuss the opportunities of the methodical approach and some general problems and limits of the application of a LCA. In conclusion, we found environmental advantages for the use of grass as an alternative resource in the German paper production industry, especially in the fields of transport and water consumption.
Defect evolution in thermal barrier coating systems under multi-axial thermomechanical loading
(2005)
In service, gas turbine components with thermal barrier coatings experience high cyclic mechanical and thermal loading. Important, but not yet considered sufficiently, are the multi-axial stresses arising from thermal gradients. In this study, multi-axial stresses were simulated in laboratory experiments using a specially designed test rig. Cyclic thermomechanical fatigue experiments with radial thermal gradients (TGMF) were performed on tubular specimens consisting of a directionally densified super-alloy substrate, a NiCoCrAlY bond coat, and a ceramic thermal barrier coating (TBC). The test setup enables surface temperatures of 1000 °C, temperature differences over the whole wall thickness of the specimen of about 170 °C, and high heating and cooling rates.
The Project SupraMetall: Towards Commercial Fabrication of High-Temperature Superconducting Tapes
(2014)
The aim of the joint industrial and academic project “SupraMetall” is to enable the large scale production of superconducting tapes. This is a report of the recent achievements in the production of cube textured metal substrates and the coating techniques of the buffer and superconductive layers. The final coated conductor tapes of 2 m length reached critical current densities of 120 A/cm-width.
Advanced thermal gradient mechanical fatigue testing of CMSX-4 with an oxidation protection coating
(2008)
Frequently, turbine blades are cooled internally, which generates thermal gradients over the blade wall and, consequently, multi-axial stresses in addition to stresses due to centrifugal forces. In order to study these conditions, a new thermal gradient mechanical fatigue (TGMF) testing equipment with a lamp furnace has been developed. The advantages of this furnace are high power (16 lamps a 1000 W), controlled thermal gradients, high heating and cooling rates, and lamp lives exceeding 8000 thermal cycles. The studied material system was the single-crystal line superalloy CMSX-4 with a NiPtAl oxidation protection Coating. Different TGMF tests with a maximal surface temperature of 1050 degrees C, mechanical loads up to 400 MPa, and cycle numbers up to 9000 resulted in microstructural changes and defects, reflecting in each case the particular temperature, thermal gradient, and local stresses. For example, phase evolution of the metal coatings and rafting of the gamma/gamma’ substrate morphology was investigated. Furthermore, cracks at the inner specimen surface and at substrate pores were detected. The observed morphology and defects were related to the applied thermomechanical loads using finite element calculations.
Thermal barrier coatings (TBC,) are applied on cooled gas turbine components. Between the heated and cooled surfaces a thermal gradient develops, resulting for constraint components in high multiaxial stresses, which may exceed stresses due to mechanical loading. In order to investigate the damage behaviour of TBC systems under close to reality conditions, thermal mechanical fatigue tests with controlled thermal gradients (TGMF-tests) were performed on coated tubular specimens. The specimen substrate was made from directionally solidified nickel base superalloy IN100 DS, and the coating system comprised a NiCoCrAlY bond coat and a ceramic top coat from partially stabilized zirconia. The stress distribution over the specimen wall, which was generated in the course of one TGMF cycle, has been analysed by linear elastic Finite Element calculations. In TGMF testing specific damages occurred underneath the adherent ceramic top coat, evolving into fatigue cracks, which propagated primarily in the metallic bond coat parallel to the surface. In length sections the crack shape in this stage resembles a ‘smiley’. During further cycling the crack path deviated to the interface between BC and top coat, enhancing spallation. The ‘smiley’-crack patterns, which only occurred in TGMF but not in isothermal low cycle fatigue or thermal fatigue, are discussed with respect to the cyclic local stress distribution.
Since thermal barrier coatings (TBCs) for turbine blades suffer from bond coat oxidation and sintering of the ceramic top coat during service, quantification of TBC degradation by non destructive evaluation methods (NDE) is essential. IN617 substrates with standard NiCoCrAlY/PYSZ EBPVD TBCs were annealed at 1100 °C and measured by impedance spectroscopy. Parameters such as phase angle, total impedance, real and imaginary part were analyzed. To clearly separate bond coat oxidation from aging of the zirconia, freestanding ceramic top coats and ceramic free samples were analyzed as well. A straight correlation between the changes in the impedance spectra and the measured thickness of the thermally grown oxide was found.
