Microalloying effects in the oxidation of TiAl materials

Schumacher, G.; Dettenwanger, F.; Schütze, M.; Hornauer, U.; Richter, E.; Wieser, E.; Möller, W.

doi:10.1016/s0966-9795(99)00032-1

Cited by 79 publications

(34 citation statements)

References 15 publications

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“…These values are typical values for the growth kinetics of a pure alumina layer. Values are in agreement with previous determinations carried out with other alloys known as alumina formers [42]. It was observed that the curves became linear after a small delay except for the g-MET 100 alloy and the curves did not cross the ordinate.…”

Section: Long-term Exposure Tests Under Laboratory Airsupporting

confidence: 92%

Influence of alloy compositions on the halogen effect in TiAl alloys

Masset

Neve

Zschau

et al. 2008

Materials & Corrosion

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F-implantation concentration profile simulations were carried out and the influence of the ion fluence, implantation energy as well as the alloy composition were investigated. For alloys with Al contents between 40 and 50 at% the conditions to get the halogen effect were assessed by thermodynamic calculations. According to the thermodynamic predictions the implantation parameters were kept constant in this composition range. The implanted alloys were exposed in laboratory air over 4000 h. With the implantation parameters used (20 keV and 1 Â 10 17 F/cm 2 ), the halogen effect was found to be efficient over 4000 h. The oxide growth kinetic constants were measured and vary between 1.2 and 2.7 Â 10 À13 g 2 / cm 4 /s.

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Section: Long-term Exposure Tests Under Laboratory Airsupporting

confidence: 92%

Influence of alloy compositions on the halogen effect in TiAl alloys

Masset

Neve

Zschau

et al. 2008

Materials & Corrosion

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“…[6,[10][11][12] This model assumes that the presence of a well defined amount of halogen in the metal subsurface zone leads to the preferential formation of aluminium halides which diffuse in outward direction into voids or cavities in the oxide scale where at positions of increasing oxygen partial pressure the metal halides become converted into alumina by the oxygen present.…”

Section: Gas Phase Transport Modelmentioning

confidence: 99%

Thermodynamic Assessment of the Alloy Concentration Limits for the Halogen Effect of TiAl Alloys

Masset

Schütze

2008

Adv Eng Mater

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The development of TiAl intermetallics is mainly motivated by the potential of weight savings due to their low density. The latter ranges between 3.6 g cm -3 for c-TiAl [1] and 4.3 g cm -3 for a 2 -Ti 3 Al [1,2] whereas those of nickel-based super alloys or steels, used in structural applications, are close to 8 g cm -3 (e.g. 8.3 g cm -3 for single crystal Ni-base alloy [3] ). These materials possess good mechanical properties comparable to nickel base super alloys, even at high temperature. This fact proposes them as serious candidates for the use in high temperature applications such as air-foils in turbine engines for aeronautic applications, or rotors for turbochargers as well as exhaust valves for the automotive industry. However, it is known that the degradation of the mechanical properties of TiAl base alloys due to environmental embrittlement resulting from high temperature oxidation is still a critical issue for industry if titanium aluminide alloys are chosen as a substitute for Ni-based superalloys. Especially, this point is true for the aeronautical industry where materials have to face severe thermal cyclic as well as environmental service conditions. Indeed high temperature oxidation of TiAl base alloys leads to the formation of a (Al 2 O 3 / TiO 2 /TiN) mixed oxide scale which is non protective for long term service. [4] In order to improve the oxidation resistance of titanium aluminides, several studies on surface treatments have been performed (alloying with a third element, overlay coatings, pre-oxidation, anodisation, metallic ion implantation of third elements) and were reviewed by Yang et al. [2] Such surface modifications improve the oxidation resistance but the benefit remains limited with time and is not always obvious for thermocyclic conditions. Moreover, thick coatings may modify the mechanical properties of the alloy by the formation of brittle phases at the alloy surface. It should be emphasized that with all the previous treatments, no long term (over thousands of hours) effect was observed.An interesting alternative consists in the surface treatment by halogens. [5,6] Two models have been proposed to explain the beneficial effect of halogens applied to TiAl alloys although halogens are usually known to be strong corrosive agents for metals especially in the temperature range of interest: [7] Lattice Doping Model Taniguchi [8] proposed the "lattice doping model" in which it is postulated that two chlorine anions could annihilate an oxygen vacancy in the oxide scale. However results from direct implantation of chlorine into the oxide scale by Schumacher et al. [9] did not sustain this hypothesis. Gas Phase Transport ModelAs an alternative to the lattice doping model a new model called "gas phase transport model" was proposed and progressively ascertained. [6,[10][11][12] This model assumes that the presence of a well defined amount of halogen in the metal subsurface zone leads to the preferential formation of aluminium halides which diffuse in outward direction into voids or cavities ...

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“…They formed a mixed oxide/nitride scale (TiO 2 /TiN/Al 2 O 3 ) during high temperature oxidation in air which was non protective and fast growing [9]. The oxide scale after halogen treatment was much thinner and consisted of a protective Al 2 O 3 scale [10]. This scale was formed by the selective transport of Al via gaseous halides which were finally oxidised to Al 2 O 3 [11].…”

Section: Resultsmentioning

confidence: 99%

Improving the oxidation resistance of γ‐titanium aluminides by halogen treatment

Donchev

Schütze

2008

Materials & Corrosion

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A. Donchev * and M. Schü tzeIntermetallic alloys based on TiAl are candidates for several structural high temperature applications but their oxidation resistance is limited to temperatures below 800 8C. In this paper the results of high temperature oxidation and creep tests will be presented and discussed. The treatment with halogens improves the oxidation resistance of these alloys up to 1050 8C. A thin protective Al 2 O 3 -layer is formed after treatment with halogens instead of the mixed TiO 2 /Al 2 O 3 /TiN scale typically grown on these alloys. This alumina layer protects the component under isothermal and thermocyclic conditions. The protective effect is stable up to at least 8760 h. Creep tests of halogen treated materials at high temperatures showed no effect on the creep behaviour. Automotive turbocharger rotors were exposed at 1050 8C in air with and without fluorine-treatment for demonstration of real parts. Ã A. Donchev, M. Schütze DECHEMA e.V. Karl-Winnacker-Institute,

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Microalloying effects in the oxidation of TiAl materials

Cited by 79 publications

References 15 publications

Influence of alloy compositions on the halogen effect in TiAl alloys

Influence of alloy compositions on the halogen effect in TiAl alloys

Thermodynamic Assessment of the Alloy Concentration Limits for the Halogen Effect of TiAl Alloys

Improving the oxidation resistance of γ‐titanium aluminides by halogen treatment

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