Viscosity control of borosilica by Fe doping in Mo-Si-B environmentally resistant alloys

Multiphase Mo-Si-B alloys comprised of Mo(ss), Mo3Si (A15), and Mo5SiB2 (T2) phases offer attractive high-temperature mechanical properties with some capability to resist oxidation via production of a borosilica surface layer. In previous work, Fe additions into Mo-rich Mo-Si-B alloys appreciably limited transient oxidation, where the major mass change occurs, by enhancing the fluidity of borosilica. In the current study, the mechanism for borosilica modification is attributed to non-bridging oxygen (NBO) production and retention by Fe addition. An oxidation kinetics model is developed for Mo-Si-B alloys with Fe additions that can be extended to other oxidation-resistant refractory metal systems.