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-Mo 5SiB2 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.
- Mo-Si-B alloys
- Ultra-high temperature materials