Influence of alloy compositions on the halogen effect in TiAl alloys

Masset, Patrick J.; Neve, S.; Zschau, H.‐E.; Schütze, M.

doi:10.1002/maco.200804145

Cited by 20 publications

(25 citation statements)

References 30 publications

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“…[15] The writing of the conservative fluxes at the interface oxide/metal requires basic hypotheses detailed hereafter. The oxygen flux at the oxide/metal interface J O)x=0 is determined by the alumina formation.…”

Section: Models and Basic Hypothesesmentioning

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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Section: Models and Basic Hypothesesmentioning

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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“…Turbine blades made of the intermetallic TNB-alloy (Ti -(44-46) at.% Al - (4)(5)(6)(7)(8) at.% Nb -(0-0.2) at.% C) with overall dimensions of 5 Â 2 Â 3 cm 3 were cut into segments with surface area of 2 Â 3 cm 2 . They were manually polished with 1200 grit SiC paper.…”

Section: Methodsmentioning

confidence: 99%

“…As a second fluorination technique spraying with F-containing aerosol (described in Ref. [7]) was applied. The fluorine does not diffuse into the alloy before the specimen is heat treated.…”

Section: Fluorination Methodsmentioning

confidence: 99%

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Measurements of fluorine depth‐profiles on TiAl turbine blades using ion beam analytical techniques

Neve¹,

Masset²,

Zschau³

et al. 2011

Materials & Corrosion

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Intermetallic TiAl alloys are foreseen to substitute Ni-based alloys in several high-temperature applications such as turbine blades for aeronautics. Because of their low density the mass of these components could be reduced by half. However, a mixed oxide scale of TiO 2 and Al 2 O 3 which provides no oxidation protection is growing at temperatures above 700 8C. By means of the halogen-effect the high-temperature oxidation resistance of TiAl alloys can be improved by orders of magnitude. Therefore fluorine was introduced into turbine blades using two different chemical fluorination methods. The application of a fluorine treatment promotes the growth of a pure and dense alumina scale which prevents the alloy from increased oxidation. In previous work it has been shown that an appropriate fluorine content after oxidation and its location beneath the surface are indicators of a successful fluorine effect. In the present work, the fluorine content was measured before and after oxidation of TNB alloy as a function of depth by using proton induced gamma-ray emission (PIGE) in a specially designed vacuum chamber at the 2.5 MV van-de-Graaff accelerator at the IKF. Additionally, composition and thickness of the oxide scale was determined by Rutherford backscattering spectrometry (RBS). The ion beam techniques are non-destructive and thus offer a method for quality assurance of the halogen treatment.

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“…Known issues are the high production costs for components made of TiAl [3] and their insufficient oxidation resistance at elevated temperatures above 700°C [4]. The latter can be overcome by using the innovative halogen effect as was already reported in several papers [5][6][7][8][9][10][11][12]. After doping the surface with F-ions and pre-oxidizing at high temperatures, the formation of a protective alumina scale can be achieved.…”

Section: Introduction *mentioning

confidence: 99%

Development of a PIGE-Detection System for in-situ Inspection and Quality Assurance in the Evolution of Fast Rotating Parts in High Temperature Environment Manufactured from TiAl

et al. 2013

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Intermetallic γ-titanium aluminides are a promising material in high temperature technologies. Their high specific strength at temperatures above 700°C offers the possibility for their use as components of aerospace and automotive industries. With a specific weight of 50% of that of the widely used Ni-based superalloys TiAl is very suitable as material for fast rotating parts like turbine blades in aircraft engines and land based power stations or turbocharger rotors. Thus lower mechanical stresses and a reduced fuel consumption and CO 2 -emission are expected. To overcome the insufficient oxidation protection the halogen effect offers an innovative way. After surface doping using F-implantation or liquid phase-treatment with an F-containing solution and subsequent oxidation at high temperatures the formation of a protective alumina scale can be achieved. By using non-destructive ion beam analyses (PIGE, RBS) F was found at the metal/oxide interface. For analysis of large scale components a new vacuum chamber at the IKF was installed and became operative. With this prototype of in-situ quality assurance system for the F-doping of manufactured parts from TiAl some performance test measurements were done and presented in this paper.

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Influence of alloy compositions on the halogen effect in TiAl alloys

Cited by 20 publications

References 30 publications

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

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

Measurements of fluorine depth‐profiles on TiAl turbine blades using ion beam analytical techniques

Development of a PIGE-Detection System for in-situ Inspection and Quality Assurance in the Evolution of Fast Rotating Parts in High Temperature Environment Manufactured from TiAl

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