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Influence of different annealing processes on the oxidation behaviour of γ-TiAl

Ebach-Stahl, Andrea and Fröhlich, Maik and Leyens, Christoph (2008) Influence of different annealing processes on the oxidation behaviour of γ-TiAl. 7th International Conference on Microscopy of Oxidation, 2008-09-15 - 2008-09-17, Chester, UK.

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Titanium aluminides are an attractive material for aerospace as well as automotive industry particularly due to their low mass density and good mechanical properties in the temperature range between 700°C and 900°C. But above 750°C titanium aluminides show a poor oxidation behaviour caused by fast growing titania. In this study particularly thermally pre-treated γ-TiAl was investigated with regard to the oxidation resistance in comparison to non pre-treated material. The Ti-45Al-8Nb alloy was exposed under various conditions, such as different atmospheres (high vacuum, Ar- and H<sub>2</sub>-atmosphere), temperature (900°C and 1000°C) and time (1-200h). Under high vacuum conditions (10<sup>-6</sup>mbar) only phase transformation in the surface region took place. The lamellar structure of the base material changed into single α<sub>2</sub>-Ti<sub>3</sub>Al with oxygen enrichment on top. Under Ar-atmosphere (50mbar) mainly nitrides were formed at the surface with an α<sub>2</sub>-layer and σ-Nb<sub>2</sub>Al precipitations below. During annealing γ-TiAl in hydrogen under atmospheric pressure (1040mbar) the material oxidized relatively fast. A dense TiO<sub>2</sub> layer was formed on top, followed by a mixed oxide scale and a relatively thick region of alumina and σ-Nb<sub>2</sub>Al precipitations in an α<sub>2</sub>-Ti<sub>3</sub>Al matrix. Several samples of these various thermally pre-treated materials were tested by cyclic oxidation at 900°C in air for investigating the oxidation behaviour. The microstructures of the formed oxides of pre-treated and non pre-treated γ-TiAl are comparable. The material pre-treated under high vacuum conditions exhibited the lowest oxidation rate, while the mass gain of the specimens annealed under Ar-atmosphere increased rapidly in the first cycles. All pre-treated specimens exceeded a lifetime of 600 cycles at minimum. The reference material showed spallation already after 520 cycles. The microstructure and phase formation of all annealed and tested samples were investigated by SEM and EDX.

Item URL in elib:https://elib.dlr.de/56459/
Document Type:Conference or Workshop Item (Speech)
Title:Influence of different annealing processes on the oxidation behaviour of γ-TiAl
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Date:17 September 2008
Open Access:No
Gold Open Access:No
In ISI Web of Science:No
Keywords:titanium aluminides, vacuum annealing, argon annealing, hydrogen annealing, oxidation behaviour, pre-treatment
Event Title:7th International Conference on Microscopy of Oxidation
Event Location:Chester, UK
Event Type:international Conference
Event Dates:2008-09-15 - 2008-09-17
Organizer:University of Liverpool, University of Birmingham
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Aeronautics
HGF - Program Themes:Propulsion Systems (old)
DLR - Research area:Aeronautics
DLR - Program:L ER - Engine Research
DLR - Research theme (Project):L - Turbine Technologies (old)
Location: Köln-Porz
Institutes and Institutions:Institute of Materials Research > High Temperature and Functional Coatings
Deposited By: Ebach-Stahl, Andrea
Deposited On:03 Dec 2008
Last Modified:27 Apr 2009 15:32

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