Oxidation behavior and mechanical properties of Ti-enriched MoSiBTiC alloy
July 17-21, 2016
Mo-Si-B alloys are one of leading candidates for ultra-high-temperature applications. Macroalloying of Ti to the Mo-Si-B systems improves both strength/density ratio and high-temperature oxidation resistance. However, the study for Ti-added Mo-Si-B alloys have been still limited very much. In this study, Ti-enriched MoSiBTiC alloy with the composition of 38Mo-17Si-5B-20Ti-10TiC (at.%) was addressed from the viewpoint of oxidation and high temperature deformation.
Alloy ingots of the 38Mo-17Si-5B-20Ti-10TiC alloy were prepared by conventional Ar arc-melting. Heat treatment was carried out in vacuum at 1600 or 1700 °C for 24 h. It was found that both the as-cast and heat-treated samples are composed of five phases, i.e., Mo solid solution, Mo3Si, Mo5SiB2, Ti5Si3 and TiC. Micro-cracks were often observed across Ti5Si3 phase, which were generated by thermal stress caused by the strong thermal expansion anisotropy of Ti5Si3. Oxidation behavior was investigated through the specific weight change against time at 1100 and 1300 °C in the atmosphere of pO2/pAr=0.25. The alloy displayed relatively good oxidation resistance. The oxidation rate coefficient obtained from the oxidation curves was below 10-2 g2m-4s-1 even at 1300 °C. This value is comparable to that of the TMS173 nickel-based SX superalloy. Mechanical property was examined by high-temperature compression tests. At 1400 °C, the peak stress reached over 700 MPa, which is at the same level as that of 1st-generation MoSiBTiC alloys . Mechanical properties would be improved by microstructure controlling because the micro-cracking in Ti5Si3 degrades the strength and toughness of the alloy. Hot-working should be effective to destroy the inhomogeneous cast microstructure and facilitate microstructure refinement for the Ti-enriched MoSiBTiC alloy.
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Mi Zhao, Kyosuke Yoshimi, and Kentaro Yokoyama, "Oxidation behavior and mechanical properties of Ti-enriched MoSiBTiC alloy" in "Beyond Nickel-Based Superalloys II", Chair: Dr Howard J. Stone, University of Cambridge, United Kingdom Co-Chairs: Prof Bernard P. Bewlay, General Electric Global Research, USA Prof Lesley A. Cornish, University of the Witwatersrand, South Africa Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/superalloys_ii/21