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Improvement of the High Temperature Oxidation Resistance of γ-TiAl by means of Si-based Coatings

Fröhlich, Maik and Ebach, Andrea and Braun, Reinhold and Leyens, Christoph (2007) Improvement of the High Temperature Oxidation Resistance of γ-TiAl by means of Si-based Coatings. In: Ti-2007 Science and Technology, Volume II, pp. 1233-1236. The Japan Institute of Metals. Ti-2007, 2007-03-06 - 2007-07-06, Kyoto, Japan.

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Abstract

Recent trends in aerospace as well as in automotive industry lead to the use of light weight materials especially applied in highly stressed components. Thereby γ-TiAl becomes more and more interesting because of the attractive mechanical properties under service conditions at temperatures up to 900°C. However, the oxidation resistance of γ-TiAl alloys decreases rapidly at temperatures above 750°C due to a fast formation of TiO<sub>2</sub>. Reducing the formation of non-protective titanium oxide is the primary objective to improve the resistance of titanium aluminides against oxidation. In this study the affinity of titanium to form oxides was reduced by forming thermodynamically stable titanium silicides. Two coatings, pure Si and Ti-75at%Si, were deposited on the γ-TiAl base material by means of magnetron sputter techniques. To induce formation of silicides, the coating systems were pre-treated by air exposure for 100h at 750°C or annealed in vacuum (pressure of 10<sup>-6</sup>mbar) for 100h at 1000°C. The oxidation resistance of the coatings was tested at 900°C and 950°C using a cyclic testing procedure: 1h heating and 10 min cooling down to 60°C. After 10, 100 and 1000 cycles (or failure) the samples were investigated by means of SEM and EDX as well as XRD to analyse the microstructure evolution and phase formation in course of time. After pre-treatment at low atmospheric pressure the most thermodynamically stable TiSi phase, i.e. Ti<sub>5</sub>Si<sub>3</sub>, has been formed. It resulted in a minimum lifetime of the coating systems of 1000 cycles at 900°C and 950°C. Uncoated γ-TiAl already failed after 520 cycles at 900°C and after 40 cycles at 950°C. The samples pre-oxidised at 750°C showed TiSi<sub>2</sub>, TiSi and Ti<sub>5</sub>Si<sub>4</sub> phase formation, which are less stable than Ti<sub>5</sub>Si<sub>3</sub>. Additionally, a thick oxide scale was formed which grows much slower during cyclic testing. Despite a higher oxidation rate of the pre-oxidised samples, only one specimen failed after 440 cycles when exposed at 950°C.

Item URL in elib:https://elib.dlr.de/44525/
Document Type:Conference or Workshop Item (Speech, Paper)
Title:Improvement of the High Temperature Oxidation Resistance of γ-TiAl by means of Si-based Coatings
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Fröhlich, MaikUNSPECIFIEDUNSPECIFIED
Ebach, AndreaUNSPECIFIEDUNSPECIFIED
Braun, ReinholdUNSPECIFIEDUNSPECIFIED
Leyens, ChristophBrandenburgische Technische Universität Cottbus, Konrad-Wachsmann-Allee, 03046 CottbusUNSPECIFIED
Date:2007
Journal or Publication Title:Ti-2007 Science and Technology
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Volume:Volume II
Page Range:pp. 1233-1236
Editors:
EditorsEmail
Niiomi, M.UNSPECIFIED
et al., UNSPECIFIED
Publisher:The Japan Institute of Metals
Status:Published
Keywords:TiAl, Oxidationschutzschichten, Ti-Si
Event Title:Ti-2007
Event Location:Kyoto, Japan
Event Type:international Conference
Event Dates:2007-03-06 - 2007-07-06
Organizer:The Japan Institute of Metals
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: Fröhlich, Maik
Deposited On:27 Nov 2008
Last Modified:27 Apr 2009 13:02

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