Abstract
The effectiveness of coatings (MoSi 2 on TZM-Mo (where TZM is Mo-0.5Ti-0.08Zr-0.03C maximum) and 24Ti-24Co-52Si on unalloyed molybdenum) in preventing oxidation of the base metal was evaluated at temperatures between 870 and 1425 °C in still air. At temperatures of 1205 °C and above, the effective life of the MoSi 2 coating was equal to or longer than the time required for the protective MoSi 2 layer to be converted to Mo 5Si 3 which is a non-protective phase. At lower temperatures the effective life of the MoSi 2 coating was limited by the presence of defects and was shorter than the life predicted from interdiffusion considerations. The protective life of the 24Ti-24Co-52Si coating was less than that of the MoSi 2 coating at all test temperatures. Failures in the 24Ti-24Co-52Si coating are believed to originate at cracks that permit subsurface oxidation; interdiffusion is not a limiting factor in the protective life of this coating.
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