Prediction of Thermodynamic Properties of Mo-Si-B Alloys from First-Principles Calculations
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OVER the last decades, the development of high-temperature materials for the power generating industry (i.e., for stationary gas turbines) or aircraft engines has become a very important driving force of our modern society. High-melting nickel-based superalloys are the backbone of this industry and have led to the engine and turbine designs applied in present military and civil airplanes as well as stationary gas turbines. Until recently, Ni-based superalloys are the first choice for state-of-the-art turbine blade materials for high-pressure turbine applications. However, nickel-based superalloys have reached their technical application limit at turbine operating temperatures of around 1100 C.[1] Hence, heat shielding via thermal barrier coatings (TBCs) and a complex cooling system are necessary under these conditions,[2] which, however, lead to efficiency losses of the turbine.[3] There is common sense in science and economy that these S. HU¨TTER and T. HALLE are with the Institut fu¨r Werkstoff- und Fu¨getechnik, Otto-von-Guericke Universita¨t, Universita¨tsplatz 2, 39106 Magdeburg, Germany. Contact e-mail: [email protected] G. HASEMANN and M. KRU¨GER are with the Forschungszentrum Ju¨lich GmbH, Institut fu¨r Energie- und Klimaforschung, Werkstoffstruktur und Eigenschaften (IEK-2), Leo-Brandt-Straße 1, 52425 Ju¨lich, Germany. J. AL-KARAWI is with the Institut fu¨r Stro¨mungstechnik und Thermodynamik, Otto-von-Guericke Universita¨t, Universita¨tsplatz 2, 39106 Magdeburg, Germany. Manuscript submitted May 20, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
efficiency losses can only be effectively reduced by developing new high-temperature materials. Besides possible candidates such as Co-Re-Cr[4–6] and Nb-Si-Cr alloys,[7–9] multi-phase Mo-Si-B alloys are very promising candidates. Especially, alloys which are taken from the so-called Berczik triangle[10] are of central scientific interest. Those alloys feature the relatively ductile Mo solid solution (Moss) phase in combination with the two silicide phases Mo3Si and Mo5SiB2. Depending on the volume fraction of phases, those alloys combine excellent high- and ultra-high-temperature creep behavior with acceptable oxidation resistance and fracture toughness.[11–13] While the mechanical properties of Mo-Si-B alloys, such as high-temperature strength,[14–17] creep,[11,18–22] and fracture behavior,[14,23–28] are relatively well investigated, only little is known about the physical and thermodynamic properties of such alloys or their individual phases. In the past, special attention had been payed to the coefficient of thermal expansion (CTE) of, e.g., the intermetallic phases Mo5Si3 and Mo5SiB2[29–32] or of various MoSS/Mo5SiB2 alloys.[33] Most of these publications also investigated the anisotropy of the CTE, which is of special importance in high-temperature applications of multi-phase compounds with different CTE. The elastic constants of the individual phases and compounds are also relatively well known and reported.[31,32,34] Previously, ab initio methods have
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