Thermomechanical Fatigue of the TiAl Intermetallic Alloy TNB-V2
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TiAl is supposed to substitute Ni or Ti alloys in energy conversion systems, such as aero engines. These components are subjected to thermomechanical fatigue (TMF), whereas this mechanical behaviour may substantially differ from isothermal low cycle fatigue (LCF). Therefore, it is necessary to assess TMF properties, in order to establish a reliable and precise lifetime prediction model. In this study the γ-base TiAl intermetallic alloy TNB-V2 was subjected to fully-reversed TMF tests under total strain control at strain amplitude of 0.7%, accompanied by LCF tests in air and vacuum. Temperature ranged from 550°C to 850°C. In TMF tests a continuous built-up of compressive (in-phase) or tensile (out-of-phase) mean stresses is observed. The lifetime ratio between IP and OP is 30–200, depending on temperature range. Substantially longer lifetimes of OP-TMF tests in vacuum are observed. Fracture always occurs in a transcrystalline mode. A lifetime description at 550°C based on the Basquin-Coffin-Manson equation reveals that the fatigue behaviour is governed by the amount of elastic strain even at low cycles, and the transition lifetime was found to be at 5 cycles. A damage parameter based on the equation of Smith, Watson and Topper is able to describe LCF and in-phase TMF lifetimes reasonably.
KeywordsTitanium aluminides Thermomechanical fatigue Environmental effects Lifetime description Smith-Watson-Topper equation
Financial support for this work by Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged. The authors would also like to thank their project partner for providing the material and performing complementary investigations (Dr. F. Appel and his research group, GKSS Research Centre, Geesthacht, Germany).
- 1.Appel F, Lorenz U, Paul JDH, Oehring M (1999) The mechanical properties of niobium alloyed gamma titanium aluminides. In: Kim Y-W, Dimiduk DM, Loretto MH (eds) Gamma titanium aluminides 1999. TMS, Warrendale, pp 381–388Google Scholar
- 4.Brookes SP, Kühn HJ, Skrotzki B, Sievert R, Pfetzing J, Eggeler G (2007) Axial-torsional thermo-mechanical fatigue of Ti-45Al-5Nb-0.2B-0.2C. In: Niinomi M, Akiyama S, Hagiwara M, Ikeda M, Maruyama K (eds) Ti-2007 science and technology, vol. 1. The Japan Institute of Metals, Sendai, pp 679–682Google Scholar
- 11.Appel F, Heckel TK, Christ H-J (2009) Electron microscope characterization of low cycle fatigue in a high-strength multiphase titanium aluminide alloy, Int J of Fatigue, doi:10.1016/j.ijfatigue.2009.04.001
- 15.Nickel H, Zheng N, Elschner A, Quadakkers WJ (1995) The oxidation behaviour of niobium containing γ-TiAl intermetallics in air and argon/oxygen. Mikrochim Acta 119:23–39Google Scholar
- 17.Chan KS, Kim Y-W (1991) Fracture processes in a two-phase gamma titanium aluminide alloy. In: Kim Y-W, Boyer RR (eds) Microstructure / property relationships in titanium aluminides and alloys. TMS, Warrendale, pp 179–196Google Scholar
- 20.Hertzberg RW (1976) Deformation and fracture mechanics of engineering materials. John Wiley & Sons, New YorkGoogle Scholar
- 21.Hoppe R (2008) Personal communication. GKSS Research Centre, GeesthachtGoogle Scholar
- 22.Smith KN, Watson P, Topper TH (1970) A stress-strain function for the fatigue of metals. J Mater 5:767–778Google Scholar
- 23.Dowling NE (2007) Mechanical behavior of materials. Pearson Prentice Hall, Upper Saddle RiverGoogle Scholar