Papers by Author: Daniel Renusch

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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.
Authors: Katsuyuki Yanagihara, Daniel Renusch, M. Röhrig, Michael Schütze
Abstract: Isothermal oxidation was carried out on Fe and Fe-(1.0 and 5.0mass%)Cr alloy at 800°C and 1000°C in dry (PH2O=1x10-4 atm) and wet (PH2O=0.035 atm) air. Fracture behavior of the scale was investigated using acoustic emission (AE) analysis during cooling. The water vapor content of the atmosphere has a major influence on the oxidation of the Fe-Cr alloys, whereas it has virtually no effect on the oxidation of Fe. During cooling, significant AE activity starts at about 450°C on the Fe and Fe-Cr alloys oxidized in wet air. This critical temperature is independent of sample composition, oxidation temperature and scale thickness. In the case of the oxidation of the Fe-Cr alloys in dry air, however, the critical temperature shifts to higher temperatures with increasing scale thickness and Cr content. Fracture behavior of the scale should be related to scale structure caused by sample composition and oxidation condition.
Authors: Hans Eberhard Zschau, Daniel Renusch, Patrick J. Masset, Michael Schütze
Abstract: A new method is proposed to achieve a dense protective alumina scale for Ni-base superalloys with an Al-content lower than 10 wt.% at temperatures above 1000°C. The method is based on the halogen effect. Thermodynamical calculations show the existence of a region for a positive fluorine effect at temperatures between 900-1200°C for the alloys IN738 and IN939. By using fluorine ion implantation in combination with Monte Carlo simulation of the fluorine profiles these results were transformed into a region of F-concentrations at the metal surface. A dense protective alumina scale was formed for IN738 after oxidation at 1050°C. Due to the very low Al-content no alumina scale was found for IN939.
Authors: Mario Rudolphi, Daniel Renusch, Hans Eberhard Zschau, Michael Schütze
Abstract: Thermal barrier coatings used in airplane engines or land-based gas turbines can show catastrophic failure (i. e. spallation) typically during cooldown due to thermal expansion mismatch stresses. However, it is also often noted that spallation occurs minutes, hours, or even days after the sample is cold. This type of delayed failure, called “desk top spallation” is, up to now, not fully understood and therefore a field of great interest. Because desk top failure occurs in ambient air, the working hypothesis is that water vapor from the office environment plays a role. Consequently, a number of experiments have been designed to verify this hypothesis. The experiments include more traditional approaches like acoustic emission measurements during cyclic oxidation, but also innovative new approaches like acoustic emission during water drop testing, and hydrogen detection at the interface to the thermally grown oxide using ion beam techniques.
Authors: Michael Schütze, M. Malessa, Daniel Renusch, P.F. Tortorelli, Ian G. Wright, R.B. Dooley
Abstract: In the high temperature oxidation of metallic alloys oxide scale strains and in particular critical scale strains play a key role with regard to scale adherence. Scale spallation/exfoliation is a vital issue for not only long term alloy performance but also steel sheet production. In many cases materials selection is based on thermodynamic considerations and short term laboratory data, not taking into account changes in the oxidation mechanisms resulting from stresses induced by thermal cycles, oxide growth, specimen or component geometry, or other operational factors. This paper presents a very concise summary of the present knowledge in the form of an approach to a comprehensive scale failure model which is based on a number of microscopic and macroscopic system parameters. This failure model is part of an on-going work which aims at a computer-assisted assessment of oxide scale mechanical reliability.
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