Oxide scale formation and isothermal oxidation behavior of Mo-Si-B intermetallics at 600-1000°C

Initial scale formation in the range 600-1000 degrees C and isothermal oxidation behavior at 1000 degrees C was investigated for Mo-Si-B intermetallics containing 81-88 wt% molybdenum. All compositions exhibited an initial transient oxidation period consisting of a mass gain due to MoO3 and SiO2 formation, followed by a rapid mass loss starting at 750 degrees C due to MoO3 volatilization. After the initial transient oxidation period, oxidation proceeded at a much slower rate. During isothermal oxidation at 1000 degrees C the oxidation rate was found to vary inversely with the ratio of B/Si in the intermetallic, indicating that viscous flow of the scale was an important factor in determining the isothermal oxidation rate at 1000 degrees C. (C) 1999 Elsevier Science Ltd. All rights reserved.