Effects of Solid Solution Strengthening Elements Mo, Re, Ru, and W on Transition Temperatures in Nickel-Based Superalloy
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SINCE the introduction of nickel-based superalloys in industrial and aeronautical gas turbine applications, alloy development has mainly been performed on a ‘‘trial-and-error’’ basis. This experimental approach is expensive and time consuming with a relatively low NILS C. RITTER, JAN C. SCHAUER, DANIEL GRUBER, CAROLIN KOERNER, and ROBERT F. SINGER are with the Institute of Metals Science and Engineering, FAU Universita¨t Erlangen, Erlangen, Germany. Contact e-mail: [email protected] ROMAN SOWA is with the MTU Aero Engines Polska, Rezeszow, Poland and also with the Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland. THOMAS GOEHLER is with the MTU Aero Engines AG, Munich, Germany. RALF RETTIG is with the Institute of Metals Science and Engineering, FAU Universita¨t Erlangen and also with the ThermoCalc Software AB, Solna, Sweden. ERWIN POVODEN-KARADENIZ is with the Institute of Materials Science and Technology, TU Vienna, Vienna, Austria. Manuscript submitted May 3, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
chance of success. In recent years, chemical optimization of nickel-based superalloys has often been supported by computational methods.[1–4] These new numerical approaches are based on different mathematical search and optimization algorithms, which use semi-empirical and physical-based models to predict certain relevant properties. The development of alloys, such as STAL15,[1] TMS-238,[2] SGLS3,[3] and ERBO/15[4] for blade applications with the use of these new techniques has demonstrated their effectiveness for future alloy development. One main physical property model used in such programs is the calculation of phase diagrams (CALPHAD) method. This method is based on minimizing the free energy of the investigated material at a certain temperature, composition, and pressure. Many detailed reports on the CALPHAD approach have been published.[5–8] In principle the thermodynamic information regarding the structure and phase stability is stored in databases, which can be used in commercial software, such as Thermo-Calc, MatCalc, Pandat, FactSAGE,
and JMatPro. For example, with the aid of the CALPHAD application it is possible to calculate the phase composition and phase fraction dependence on alloy composition and temperature. This feature allows the user to design an alloy for specific demands if one is able to link the chemical composition and phase fraction to the mechanical properties. The creep resistance of nickel-based superalloys is a basic feature in alloy development. Creep deformation at high temperatures and low stresses are controlled by thermally activated dislocation-motion in the c-matrix phase (e.g., Reference 9). Furthermore, precipitation strengthening, provided by a high volume fraction of fine precipitates, and solid solution strengthening of the matrix phase are important. In particular, Mo, W, and especially Re[10,11] are well known to increase the mechanical strength of the matrix phase and consequently the overall creep performance. The advantage of Ru is that
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