Effect of Ti (Macro-) Alloying on the High-Temperature Oxidation Behavior of Ternary Mo–Si–B Alloys at 820–1,300 °C
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The aim of the present investigation was to gain an initial understanding of the effect of (macro-) alloying with Ti on the oxidation behavior of Mo–Si–B alloys in the ternary phase region of Mo_ss–Mo3Si–Mo5SiB2 at 820–1,300 °C. Motivated by recent studies and thermodynamic calculations, the alloy compositions Mo–9Si–8B–29Ti (at.%) and Mo–12.5Si–8.5B–27.5Ti (at.%) were selected and synthesized by arc-melting. Compared to the reference alloy Mo–9Si–8B, superior initial oxidation rates at 1,100–1,300 °C as well as a significant density reduction by nearly 18 % were observed. Due to enhanced initial evaporation of MoO3 and mainly inward diffusion of oxygen, a borosilicate-rutile duplex scale with a continuous TiO2 phase had formed. Detailed investigations of the oxidation mechanism by SEM, EDX, XRD and confocal micro-Raman spectroscopy indicated that Ti alloying is promising with regard to further improvement of the oxidation resistance as well as the strength-to-weight ratio of Mo–Si–B alloys.
KeywordsUltra-high temperature materials Mo–Si–B alloys Titania Silica
Financial support by Deutsche Forschungsgemeinschaft (DFG) within the framework of the research unit 727 “Beyond Ni-Base Superalloys” is gratefully acknowledged. The authors would like to thank E. P. George and H. Bei for the preparation of the alloys in ORNL.
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