The Science, Technology, and Implementation of TiAl Alloys in Commercial Aircraft Engines
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The Science, Technology, and Implementation of TiAl Alloys in Commercial Aircraft Engines B. P. Bewlay1, M. Weimer2, T. Kelly2, A. Suzuki1, and P.R. Subramanian1 1
GE Global Research, Niskayuna, NY, United States.
2
GE Aviation, Cincinnati, OH, United States.
ABSTRACT The present article will describe the science and technology of titanium aluminide (TiAl) alloys and the engineering development of TiAl for commercial aircraft engine applications. The GEnxTM engine is the first commercial aircraft engine that is flying titanium aluminide (alloy 4822) blades and it represents a major advance in propulsion efficiency, realizing a 20% reduction in fuel consumption, a 50% reduction in noise, and an 80% reduction in NOx emissions compared with prior engines in its class. The GEnxTM uses the latest materials and design processes to reduce weight, improve performance, and reduce maintenance costs. GE’s TiAl low-pressure turbine blade production status will be discussed along with the history of implementation. In 2006, GE began to explore near net shape casting as an alternative to the initial overstock conventional gravity casting plus machining approach. To date, more than 40,000 TiAl low-pressure turbine blades have been manufactured for the GEnxTM 1B (Boeing 787) and the GEnxTM 2B (Boeing 747-8) applications. The implementation of TiAl in other GE and non-GE engines will also be discussed. INTRODUCTION Titanium aluminide (TiAl)-based alloys have received considerable attention for highperformance applications in the aerospace and automotive industries. There have been recent articles by Clemens [1], Wu [2], and Lasalmonie [3] that describe the state of the art of TiAl alloys and the challenges to implementation. In the last two years, TiAl has been introduced into service by GE in commercial aircraft engines as a new lightweight low-pressure turbine (LPT) blade material. Figure 1(a) shows a photograph of a TiAl LPT blade as used in the GEnxTM engine, and Figure 1(b) shows a photograph of the assembly of TiAl LPT blades as used in an early GE CF6 test engine; the data provided by this CF6 test established the foundations for the use of TiAl in the GEnxTM engine. From the early TiAl research [1-5] it became evident that the principal advantages of TiAlbased alloys are low density (3.9–4.2 g/cm3, depending on composition), high specific strength, high specific stiffness and improved creep, oxidation resistance, and burn resistance (in comparison with conventional titanium alloys) properties up to 800°C. At temperatures between 600 and 800°C, TiAl alloys have higher specific strength than conventional titanium alloys.
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Figure 2 shows the specific tensile strength of second- and third-generation TiAl alloys from room temperature to 800°C [1, 4]. Figure 2 shows that TiAl has a higher specific strength than alloy steels or Ni-based super-alloys. While the specific strength of TiAl is higher than that of competing materials, the room-temperature ductility is poor, typically ~1%. The low ductility has been considered to
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