Papers by Author: Hans Eberhard Zschau

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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: Sven Neve, Kurt Stiebing, Lothar P.H. Schmidt, Hans Eberhard Zschau, Patrick J. Masset, Michael Schütze
Abstract: Using the halogen effect TiAl-alloys can be protected against high-temperature oxidation. Two different fluorination methods were applied to turbine blades. The mass increase due to oxidation can be drastically reduced compared to untreated specimen. A new vacuum chamber for ion beam analysis was developed to analyze the real parts. Using PIGE-technique the F-content as a function of depth before and after oxidation was detected. Thickness and composition of the oxide scale were measured by RBS. Both ion beam methods were non destructive and thus enabled for the first time quality assurance of the halogen treatment on real components.
Authors: Hans Eberhard Zschau, Michael Schütze
Abstract: The oxidation protection of TiAl-alloys at temperatures above 750°C can be improved by the fluorine effect. The results of thermodynamical calculations predict a corridor for a positive fluorine effect. Ion implantation of F was performed because of giving the best results. After a high F-loss during heating a thin protective alumina scale acts as a diffusion barrier. The F-depth profiles show a distinct maximum at the metal/oxide interface. The diffusion coefficient of F in TiAl for 900°C was determined. The stability of the F-effect after long oxidation time at 900°C and 1000°C can be explained by the existence of a constant F-amount at the metal/oxide interface ensuring a slow growth of the alumina scale. The fluorine effect was also applied to Ni-base superalloys to improve their high temperature oxidation resistance by forming a dense continuous protective alumina scale.
Authors: Hans Eberhard Zschau, Patrick J. Masset, Michael Schütze
Abstract: A new method for the oxidation protection of Ni-base superalloys with relatively low Al-content is proposed. By using the halogen effect the Al activity on the surface can be increased. Thus, the formation of a pure protective alumina scale becomes possible. The alloys IN738 and IN939 are considered in the present paper. Thermodynamic calculations for fluorine and chlorine predict the existence of the halogen effect for both alloys at temperatures between 900°C and 1200°C. The results also predict a change of the oxidation mechanism from internal alumina formation to external oxidation.
Authors: Hans Eberhard Zschau, Michael Schütze, H. Baumann, Klaus Bethge
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