Oxidation Behavior of TiAl-8Nb Turbine Blade Alloy
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ODUCTION
GOOD heat-resistant and oxidation-resistant properties are essential for alloys that are used for the gas turbine blade parts of jet engine,[1] because these parts are exposed to severe oxidizing conditions. Ni-based alloys have been used as turbine blade materials because of their good oxidation-resistant properties. However, the Ni-based alloys have relatively high densities and, thus, are less agreeable as turbine blade material in the aerospace field and car industry. Ti-based alloys, on the other hand, have high melting point and low density; however, the oxidation resistance of these alloys needs better understanding. c-TiAl is an intermetallic alloy and has a high melting point, good oxidation, and creep-resistant properties around 1023 K due to the stable structure of crystallization. This alloy has been used in the automobile industry[2] and in the nuclear field. However, the mechanical properties of this alloy are greatly affected by the quantity and species of additive elements.[3,4] Besides, these alloys are sensitive with respect to oxidation. In recent days, serious research efforts have been made to improve the mechanical and oxidation-resistant properties of c-TiAl alloys by additive elements.[3–6] TiAl-Nb alloy, which belongs to the next generation of alloys with improved properties, is well known to have good oxidation resistance due to the addition of Nb up to 10 at. pct.[5] Thus, this alloy can be used in applications from room temperature to 1123 K. The effect of the additive elements on the oxidation properties of TiAl has earlier been studied.[6] However, a consideration of the relevant literature shows that the oxidation mechanism of the TiAl-Nb alloys is still not fully understood. In the present work, the oxidation LIDONG TENG, Doctor, DAISUKE NAKATOMI, Master Student, and SESHADRI SEETHARAMAN, Professor, are with the Department of Materials Science and Engineering, Royal Institute of Technology, SE-10044 Stockholm, Sweden. Contact e-mail: lidong@ kth.se Manuscript submitted March 8, 2007. Article published online June 20, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
behavior of the TiAl-8Nb alloy supplied by ACCESS, Germany in connection with the EU-funded project ‘‘IMPRESS’’ has been studied. The investigations have been carried out under isothermal conditions in the temperature range of 1173 to 1473 K by thermogravimetric method. The product layer was analyzed by scanning electron microscopy (SEM) and electron dispersion spectroscopy (EDS) techniques.
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EXPERIMENTAL
A. Samples and Materials In this investigation, TiAl-Nb alloy disks (13 mm in diameter and 1 mm in thickness) were used as the samples. The detailed composition of the alloy is presented in Table I. The disk samples were finely polished, and a hole with a diameter of 2.5 mm was drilled in order to hang the sample in the thermobalance, as shown in Figure 1. The argon gas and air used in the experiments were provided by AGA GAS (Stockholm). The argon was purified by passing through a gas-cleaning system to remove mo
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