High-Temperature Creep and Oxidation Behavior of Mo-Si-B Alloys with High Ti Contents
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Multiphase alloys in the Mo-Si-B system are potential high-temperature structural materials due to their good oxidation and creep resistance. Since they suffer from relatively high densities, the current study focuses on the influence of density-reducing Ti additions on creep and oxidation behavior at temperatures above 1273 K (1000 °C). Two alloys with compositions of Mo-12.5Si-8.5B-27.5Ti and Mo-9Si-8B-29Ti (in at. pct) were synthesized by arc melting and then homogenized by annealing in vacuum for 150 hours at 1873 K (1600 °C). Both alloys show similar creep behavior at stresses of 100 to 300 MPa and temperatures of 1473 K and 1573 K (1200 °C and 1300 °C), although they possess different intermetallic volume fractions. They exhibit superior creep resistance and lower density than a state-of-the-art Ni-base superalloy (single-crystalline CMSX-4) as well as other Mo-Si-B alloys. Solid solution strengthening due to Ti was confirmed by Vickers hardness measurements and is believed to be the reason for the significant increase in creep resistance compared to Mo-Si-B alloys without Ti, but with comparable microstructural length scales. The addition of Ti degrades oxidation resistance relative to a Mo-9Si-8B reference alloy due to the formation of a relatively porous duplex layer with titania matrix enabling easy inward diffusion of oxygen.
KeywordsOxidation Resistance Creep Behavior Oxidation Behavior Creep Resistance Solid Solution Strengthen
The financial support by the Deutsche Forschungsgemeinschaft (DFG) within the framework of the research unit 727 “Beyond Ni-base Superalloys” is gratefully acknowledged. HB and EPG were supported by the U.S. Department of Energy, Office of Fossil Energy, Advanced Turbine Systems Program. The authors would also like to thank Dr. T. Gietzelt and U. Gerhards from the Institute for Micro Process Engineering at the Karlsruhe Institute of Technology for help with electron microprobe wavelength-dispersive spectroscopy measurements.
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