Elsevier

Intermetallics

Volume 13, Issue 5, May 2005, Pages 543-558
Intermetallics

Fatigue properties of TiAl alloys

https://doi.org/10.1016/j.intermet.2004.09.007Get rights and content

Abstract

The fatigue properties of TiAl alloys, namely fatigue life, cyclic stress–strain behaviour and fatigue crack growth resistance are reviewed in the present paper. The influence of different parameters (microstructure, defects, temperature and environment) on these properties is examined. Finally, some considerations on the fatigue reliability of TiAl components are proposed.

Introduction

TiAl alloys now appear as potential competitors to steels and superalloys for components in jet engines and turbines. Depending on the processing route selected to manufacture a given component, a broad range of microstructures (equiaxed γ, two-phase nearly fully lamellar, duplex) can be achieved. Now it is well established that differences in microstructural features in these alloys lead to very different balances of mechanical properties (ductility, fracture strength, fracture toughness, creep resistance, etc.) Besides, in most foreseen applications, the high-cycle and/or low-cycle fatigue resistance, as well as the crack growth resistance of the material, might be an issue. Hence, there is a need for both metallurgists and designers to get insights into the mechanisms governing the fatigue properties in TiAl alloys, in order to optimise microstructures on the one hand, and to develop relevant lifing methods on the other hand. Now, it has also to be recognised that these properties might depend on different extrinsic factors such as temperature and environment. Therefore, the development of relevant lifing methods implies an interdisciplinary research effort in order to fill the gap between the basic characterisation of cyclic properties and an in-depth understanding of the fundamental mechanisms governing these properties. The present paper presents an overview of the current understanding of the community on these issues. The different fatigue properties of TiAl alloys, namely high-cycle fatigue (HCF), cyclic stress–strain (CSS) behaviour and fatigue crack growth (FCG) resistance are reviewed, with a special attention paid to the influence of parameters such as microstructure, defects, environment and temperature.

Section snippets

General features on fatigue resistance of TiAl alloys

The fatigue behaviour of TiAl-based alloys was early investigated by Sastry and Lipsitt [1]. The SN curves determined for a binary Ti–36.5Al (wt%) alloy with a lamellar microstructure at various temperatures are shown in Fig. 1. First, it can be noticed that, regardless of temperature, the SN curves are extremely flat. This means that a slight variation in the applied stress amplitude can lead to significant differences in the number of cycles to failure. The second point is that the fatigue

Low-cycle fatigue resistance

Recina et al. [22], [23], [24], [25] have examined the low cycle fatigue (LCF) behaviour of different alloys at 600 °C. Some of their results are presented in Fig. 9. The alloys considered are the XD45 alloy (Ti–45Al–2Mn–2Nb+0.8% vol TiB2), solidified via a β path and characterised by a randomised lamellar microstructure, a XD47 alloy (Ti–47Al–2Mn–2Nb+0.8% vol. TiB2), with a duplex microstructure where the lamellar colonies are elongated along the loading axis, a ABB alloy (Ti–48Al–2W–0.5Si)

Fatigue crack propagation

Depending on the selected processing route, different types of surface and internal defects can be present in a component at the very beginning of the service life. In addition, more severe surface defects can be introduced during service by impacts for instance. Therefore, the residual fatigue strength in presence of such defects has to be evaluated, which implies a sound description of the fatigue crack growth process in these low-fracture toughness materials. As a matter of fact, the Fatigue

Microstructural design for reliability in long-term service

The data presented above allow the definition of a fatigue and damage tolerance design methodology for this class of alloys.

Fig. 30 presents critical defect sizes for FCG and fracture determined for two characteristic microstructures as a function of the maximum stress in the case of a surface defect in a round bar fatigued at R=0.1with the stress intensity factor estimated from [73]. The critical size for propagation is derived for the effective threshold value ΔKeff,th, which is supposed to

Summary and conclusions

The different fatigue properties of TiAl alloys have been reviewed in the present paper. It has been shown that TiAl alloys, in the absence of sharp defects, exhibit an excellent fatigue resistance as characterised by an endurance ratio higher than 80% of the ultimate tensile strength. This fatigue resistance can be altered by different factors such as surface preparation, as commonly observed in conventional alloys. The low-cycle fatigue and cyclic stress–strain behaviour have received less

Acknowledgements

A part of this work was conducted within the framework of a national project (CPR ‘TiAl intermetallic’) in collaboration with LTPCM (Grenoble), CECM (Vitry), LSG2M (Nancy), GMP (Rouen), CEMES (Toulouse), LMS (Palaiseau), LMPM (Poitiers), the companies SNECMA MOTEURS and TURBOMECA, with the financial support of CNRS and DGA.

References (78)

  • V. Recina et al.

    High temperature low cycle fatigue properties of Ti–48Al–2Cr–2Nb gamma titanium: aluminides cast in different dimensions

    Scripta Mater

    (2000)
  • V. Recina et al.

    High temperature low cycle fatigue properties of Ti–48Al–2W–0.5Si gamma titanium aluminide

    Mater Sci Eng A

    (1999)
  • Y. Umakoshi et al.

    Plastic anisotropy and fatigue of TiAl PST crystals: a review

    Intermetallics

    (1996)
  • Y.S. Park et al.

    The effect of the applied strain range on fatigue cracking in lamellar TiAl alloy

    J Alloys Compd

    (2002)
  • T.S. Srivatsan et al.

    Cyclic fatigue and fracture behavior of a gamma-titanium aluminide intermetallic

    Eng Fract Mech

    (1995)
  • F. Appel et al.

    Microstructure and deformation of two-phase [gamma]-titanium aluminides

    Mater Sci Eng: R: Rep

    (1998)
  • F. Appel et al.

    Thermally activated deformation mechanisms in micro-alloyed two-phase titanium aluminide alloys

    Mater Sci Eng A

    (1997)
  • D. Haussler et al.

    In situ high-voltage electron microscope deformation study of a two-phase ([alpha]2+[gamma]) Ti–Al alloy

    Mater Sci Eng A

    (1997)
  • H.Y. Yasuda et al.

    Thermal stability of deformation substructure of cyclically deformed TiAl PST crystals

    Intermetallics

    (1996)
  • Y.S. Park et al.

    Intergranular cracking under creep-fatigue deformation in lamellar TiAl alloy

    Mater Lett

    (2002)
  • A.-L. Gloanec et al.

    Fatigue crack growth behaviour of a gamma-titanium-aluminide alloy prepared by casting and powder metallurgy

    Scripta Mater

    (2003)
  • G. Hénaff et al.

    Fatigue crack propagation resistance of a Ti–48Al–2Mn–2Nb alloy in the as-cast condition

    Mater Sci Eng

    (1996)
  • A.H. Rosenberger

    Effect of environment on the fatigue crack growth of gamma titanium aluminide alloys at ambient temperatures

    Scripta Mater

    (2001)
  • J. Petit et al.

    Stage II intrinsic fatigue crack propagation

    Scripta Metall

    (1991)
  • W.O. Soboyejo et al.

    Investigation of room-temperature and elevated-temperature fatigue crack growth in Ti–48Al

    Mater Sci Eng A—Struct Mater

    (1991)
  • W.O. Soboyejo et al.

    Mechanisms of fatigue crack growth in Ti-48Al at ambient and elevated temperature

    Scripta Metall Mater

    (1995)
  • A.L. McKelvey et al.

    On the anomalous temperature dependence of fatigue-crack growth in gamma-based titanium aluminides

    Scripta Mater

    (1997)
  • S. Lesterlin et al.

    Effects of temperature and environment interactions on fatigue crack propagation in a Ti alloy

    Scripta Mater

    (1996)
  • C. Mabru et al.

    Influence of temperature and environment on fatigue crack propagation in a TiAl-based alloy

    Eng Fract Mech

    (1999)
  • G. Hénaff et al.

    The role of crack-closure in fatigue crack propagation behaviour of a TiAl-based alloy

    Scripta Mater

    (1996)
  • A. Carpinteri

    Stress-intensity factors for semi-elliptical surface cracks under tension or bending

    Eng Fract Mech

    (1991)
  • M. Nazmy et al.

    Surface defect tolerance of a cast TiAl alloy in fatigue

    Scripta Mater

    (2001)
  • J.P. Campbell et al.

    On the growth of small fatigue cracks in [gamma]-based titanium aluminides

    Scripta Mater

    (1997)
  • S.M.L. Sastry et al.

    Fatigue deformation of TiAl base alloys

    Metall Trans A

    (1977)
  • J.M. Larsen

    Assuring reliability of gamma titanium aluminides in long-term service

  • M. Grange et al.

    TiAl G4: investment cast processing and mechanical properties

  • W.V. Vaidya et al.

    Understanding the fatigue resistance of gamma titanium aluminide

  • Berteaux O, Thomas M, François M. Effect of machining on high cycle fatigue of a gamma-TiAl Alloy. In: Euromat,...
  • J. Lindemann et al.

    Mechanical surface treatments for enhancing fatigue performance of gamma titanium aluminides at ambient and elevated temperatures

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      The last two deformation modes are supposed to need a higher critical shear stress to get activated if compared to slip of the ordinary dislocations [67]. Therefore, the dislocation structure in the Ti-48Al based alloys [1,2,4-12,64] is largely dominated by unit ½ <110] dislocations even in the grains with lower Schmid factors, whereas <101] superdislocation slip occurs also in favorably orientated grains. However, even the slip of ordinary ½ <110] dislocations does not occur smoothly.

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