Papers by Author: Michael Schütze

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Authors: Daniel Renusch, Michael Schütze
Abstract: The modeling equations used for spallation prediction are becoming increasingly more sophisticated due to the consideration of a wider range of thermal and thermo-mechanical loading conditions. Consequently, a software application would make such life time models more practical and may become a desired tool that both academic and applied researchers may want to use. As a starting point for further development a prototype software has been developed based on a simple phenomenological spallation analysis model. This software features a Windows based graphical user interface and works with other Windows applications, such as, Power Point, Excel or Origin. The software analyzes laboratory spallation life time data acquired from isothermal, thermal cyclic and/or burner rig testing and provides confidence limits and accuracy assessment of the analysis model. It further calculates the life time for a given bond coat temperature, temperature gradient across the coating, and thermal cycle frequency.
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Authors: Patrick J. Masset, Mathieu Laurent, Michael Schütze
Abstract: Surface modifications with well defined amounts of fluorine have proven to improve significantly the oxidation resistance of titanium aluminides and to offer the potential to decrease the sensibility of TiAl-based alloys against environmental embrittlement. By means of combined EPMA and SEM analyses the formation of an oxide layer on fluorine treated specimens was characterised. The thicknesses of the external oxide layer as well as the oxygen and nitrogen-rich subsurface layer were measured. Their growth kinetics was found to follow a cubic and a parabolic law, respectively. By subtracting the mass variation due to the ingress of oxygen and nitrogen into 2-Ti3Al, underneath the alumina layer, this allowed calculating the true value of the kinetic constant for the growth of a pure alumina layer on titanium aluminides.
397
Authors: Alexander Donchev, Michael Schütze
Abstract: The oxidation resistance of TiAl-alloys can be improved by several orders of magnitude by treating the surface of the materials with small amounts of halogens especially Cl and F. The oxidation mechanism changes due to the so called halogen effect. The formation of a fast growing mixed oxide scale on untreated alloys is suppressed, instead a thin protective alumina scale is formed on samples after optimum treatment. The different methods only influence the surface region of the components so that the bulk properties are not affected. Recent results achieved with complex TiAl-samples showed the potential that the fluorine effect could be used for TiAl-components in several high temperature applications e.g. jet engines. TiAl-specimens were treated with fluorine and chlorine in several ways and their performance during high temperature oxidation tests in air was investigated. Results of isothermal and thermocyclic oxidation tests are presented. The long term stability of the fluorine effect lasted for at least one year under thermocyclic exposure at 900°C in laboratory air. The results are discussed in terms of later use of the fluorine effect for technical applications.
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Authors: Patrick J. Masset, Rossen Yankov, Andreas Kolitsch, Michael Schütze
Abstract: Surfaces of titanium aluminides were treated by fluorine either physically using Plasma Immersion Ion Implantation (PI³) or chemically with a F-based polymer. By controlling the fluorination parameters, both treatments improve the oxidation resistance even in the presence of sulfur dioxide (0.1 vol%). No sulfur was detected in the oxide scale although thermodynamic calculations predict the formation of sulfides. The inward diffusion of oxygen and nitrogen in the alloy was found to be reduced in the presence of SO2.
1374
Authors: B. Pelic, D. Rafaja, Patrick J. Masset, H.J. Seifert, L. Bortolotto, Michael Schütze, G. Wolf, I. Loeh
Abstract: γ-TiAl intermetallics are attractive materials for high-temperature structural applications in the aerospace and automobile industries. However, they show environmental embrittlement at elevated temperatures that is mainly related to their low high-temperature corrosion resistance. One way how to improve the high-temperature corrosion resistance is the deposition of protective coatings on the surface of the base material. In this study, samples of a Ti-Al alloy with the chemical composition Ti-48Al-2Cr-2Nb (at.%) were covered by physically vapour deposited (PVD), by metalorganic chemically vapour deposited (MOCVD) and by high-velocity oxy-fuel (HVOF) sprayed coatings. All coatings were based on the Ti-Al alloys and contained different amounts of alloying elements. The corrosion experiments were performed in molten salts containing 75 wt.% Na2SO4 and 25 wt.% NaCl at 850°C up to 336 h. Both, PVD and CVD protected coatings reduced the changes in the mass of the samples over the corrosion time. Still, the formation of TiO2 could not be avoided, as it was confirmed by glancing-angle X-ray diffraction experiments.
301
Authors: Alexander Donchev, Michael Schütze
447
Authors: Ammar Naji, Michael Schütze
Abstract: Reformer materials are exposed to severe operating conditions at high temperature in aggressive catalyzer and combustion atmospheres. Therefore, materials used for the construction of the reformer reactor have to possess appropriate high temperature resistance. Diffusion coatings improve the high temperature resistance of materials by enrichment of the alloy surface with thermodynamically stable oxide formers. Beside conventional mono-element diffusion coatings (e.g. Al coating), multi-element diffusion coatings can be developed in a single process step. In this work we developed Al diffusion and Al-Si and Al-Si-RE (RE: reactive element Y, Ce) co-diffusion coatings on a low cost austenitic 18Cr10Ni-steel. The high temperature resistance of coated and uncoated 18Cr10Ni-steel, 20Cr31Ni-steel and 23Cr18Fe-Ni base alloy was tested in catalyzer and combustion atmosphere under cyclic operation conditions.
245
Authors: Michael Schütze
Abstract: The paper reviews the advantages of diffusion coating and the parameters deciding an optimum coating performance. Furthermore, innovative coating approaches are presented which have a significant potential beyond existing diffusion coating solutions.
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Authors: Alexander Donchev, Michael Schütze, Andreas Kolitsch, Rossen Yankov
Abstract: High temperature Ti-alloys are usually sophisticated and hence expensive. To allow the use of cheaper alloys at elevated temperatures an economic and easy to apply procedure was developed to improve their high temperature capability. The treatment consists of a combination of Al-enrichment in a shallow surface region plus additional fluorination. The Al-enrichment at elevated temperatures leads to the formation of intermetallic TiAl-phases. These phases improve the oxidation resistance of Ti-alloys but not to a sufficient extent. An additional fluorine treatment of the Al-enriched surface leads to the formation of a protective alumina scale due to the fluorine effect. In this paper results from high temperature exposure tests performed on different Ti-alloys without any treatment and with a combination of Al-treatment plus fluorination are presented. The results are discussed in the view of the use of the optimized Ti-components for several high temperature applications.
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