Early stage of oxidation of Mo₃Si by in situ environmental transmission electron microscopy

Ni-based superalloys, which have been used in aerospace and power-generation gas-turbine engines operating at high temperatures, are serving near their melting point. There is a drive to increase turbine inlet temperatures to increase overall efficiency, but the currently commercially used materials have reached their limits. With a higher melting temperature, and favorable mechanical, creep, and oxidation properties, Mo-Si-based superalloys are of interest as a new family of high-temperature materials to replace Ni-based alloys. By means of in situ environmental transmission electron microscope, the transient period of the early oxidation of Mo₃Si was investigated at the nanometer scale. As a result of a competition between loss of volatile MoO₃ and association of SiO₂ molecular units into pillars, a nanometer-sized porous SiO₂ grows at a very initial stage of the oxidation of Mo₃Si.