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In the present contribution, we describe the successful development of two ternary Mo-Si-Ti alloys with two-phase eutectic and eutectoid microstructure, respectively. In the case of Mo-20.0Si-52.8Ti (at.%), a fully eutectic microstructure consisting of body-centered cubic (bcc) solid solution (Mo,Ti,Si) and hexagonal (Ti,Mo) 5 Si 3 can be obtained in very good agreement with thermodynamic calculations. A fully eutectoid decomposed microstructure is observed subsequent to heat-treatment at 1300 °C for 200 h in the case of Mo-21Si-34Ti (at.%). For this alloy, bcc (Mo,Ti,Si) and tetragonal (Mo,Ti) 5 Si 3 appears after decomposition from the A15-type (Mo,Ti) 3 Si. Besides that, a small amount of hexagonal (Ti,Mo) 5 Si 3 forms in the silicide lamellae, too, which is attributed to Ti segregations in the as-cast microstructure. In addition to the focus on microstructure, both oxidation and creep behavior were preliminarily investigated and compared to other state-of-the-art Mo-based alloys. In the case of the eutectic alloy, a promising and unexpected oxidation resistance at 800 °C is observed whereas the eutectoid alloy exhibits catastrophic oxidation; a behavior that is typically observed under these conditions in alloys containing Mo-rich solid solution. The eutectic alloy shows an approximately one order of magnitude higher creep rate within the investigated temperature and stress range as compared to the eutectoid decomposed counterpart. This is attributed to the rather low intrinsic creep resistance of the hexagonal (Ti,Mo) 5 Si 3 and generally lower melting point of the former alloy, whereas in the latter case, creep seems to be controlled by the deformation of the bcc solid solution (Mo,Ti,Si) and the tetragonal (Mo,Ti) 5 Si 3 .

The high temperature oxidation behavior of a new family of refractory high entropy alloys (HEAs) with compositions of W-Mo-Cr-Ti-Al, Nb-Mo-Cr-Ti-Al and Ta-Mo-Cr-Ti-Al was studied at 1000°C and 1100°C. Based on these equimolar starting compositions, the main incentive of this study was to select the most promising alloy system whose properties may then be successively improved. Despite the high amount of refractory elements, all HEAs studied here showed good oxidation resistance at least during 48h of air exposure at 1000°C and 1100°C. Moderate values of mass gain and complex oxidation kinetics were observed for the W-and Nb-containing HEAs. These alloys formed inhomogeneous oxide scales possessing regions with thick and porous layers as well as areas revealing quite thin oxide scales due to the formation of discontinuous Cr-and Al-rich scales. The most promising behavior, though, was shown by the alloy Ta-Mo-Cr-Ti-Al which followed the parabolic rate law for oxide growth due to the formation of a thin and compact Al-rich layer.