A novel Mo–28Ti–14Si–6C–6B (atom %) alloy was designed for ultrahigh-temperature applications. Arc-melting and appropriate heat-treatment at 1600°C results in the targeted four-phase microstructure comprising Moss, Mo5SiB2 (T2), Ti5Si3 and TiC. Previously developed three-phase alloys, comprising Moss–T2–Ti5Si3 and Moss–T2–TiC, are outperformed by this novel alloy as an adequate balance of oxidation resistance, creep strength and fracture toughness is attained. The oxidation behavior is characterized by substantial oxide scale formation at 1200°C being accompanied by a mass loss of around -50 mg/cm2 after 100 h of cyclic oxidation. The oxide scale is found to be composed of a top TiO2 scale and an underlying duplex SiO2/TiO2 scale. Minimum creep rate of the alloy was in the order of 10–7 s–1 at 1200°C and 300 MPa and its room-temperature fracture toughness was (12.8 ± 1.2) MPa(m)1/2.
- Fracture toughness