Papers by Keyword: Halogen Effect

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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.
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.
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.
Authors: Alexander Donchev, Michael Schütze
Authors: Alexander Donchev, M. Galetz, M. Schütze
Abstract: Intermetallic light weight TiAl-alloys are expected to replace the heavy Ni-based super alloys in several high temperature applications. However until now they cannot be used at temperatures above 700°C for longer times due to their insufficient oxidation resistance. The high temperature oxidation behavior can be improved drastically for the use at temperatures up to at least 1050°C by small amounts of fluorine in the surface region of TiAl-components. A thin protective alumina layer is formed after an optimized fluorine treatment during exposure in oxidizing high temperature environments. Results of isothermal and thermocyclic high temperature oxidation tests of untreated and halogen treated TiAl-samples of new types of TiAl-alloys containing Mo, Cu and Si will be presented in this paper. These results will be compared and discussed considering the beneficial effect of fluorine for a later use as e.g. turbine blades in jet engines. Key words: Titanium aluminides, high temperature oxidation, halogen effect,
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: Aleksander Gil, Zbigniew Żurek, Adam Stawiarski, Jarosław Dąbek
Abstract: Surface treatment of TiAl alloys by the small amounts of halogens leads to the formation of the protective alumina scale. The halogens can be applied by ion techniques as well as by spraying or dipping with halogen-containing compounds. In this work the results of the oxidation in air of a Ti-47Al-6Nb alloy dipped in a fluorine-containing resin were presented. The thermal cycling runs were carried out in the temperature 900°C.
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: Aleksander Gil, Zbigniew Żurek, Adam Stawiarski
Abstract: There are several ways to improve the oxidation resistance of TiAl alloys. One of them is alloying with elements such as Nb, Ta, W, Si, Ag, Zr or Hf. However, bulk alloying influences the mechanical properties. Surface treatment of TiAl alloys by the small amounts of halogens leads to the formation of the protective alumina scale (“halogen effect”). The halogens can be applied by ion techniques (ion implantation, plasma immersion implantation) but also by spraying or dipping with halogen-containing inorganic and organic compounds. Deposition of the fluorine-containing resin on the surface of TiAl alloys is the easiest way to achieve the best results. SO2 impurity in air significantly influences oxidation behavior of TiAl alloys. In this work the results of the oxidation of a Ti-48Al-2Cr alloy coated with a fluorine-containing resin in the synthetic air and air containing 1% SO2 were presented. The oxidation runs were carried out in the temperature range 800-1000°C.
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.
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