Effect of Alloying with Niobium on Pest-Oxidation Behavior of Molybdinum Disilicide at 500 ????C

Molybdinum disilicide (MoSi2) is a promising material for applications as next generation of high temperature structural materials. Pest oxidation at 400-800 ????C is one of the obstacles in developing MoSi2 but this problem may be overcome by alloying. In this research we carried out the effect of alloying MoSi2 with niobium (Nb) at 500 ????C where the highest pest-oxidation rate happens. Polycrystalline MoSi2 was prepared by using an arc-melter in an argon atmosphere. Oxidation kinetics was studied at 500 ????C for MoSi2, MoSi2-1 at% Nb and MoSi2-2 at% Nb. Microstructural morphology of samples was studied using a scanning electron microscope. Moreover, oxide composition of the samples was determined with an energy-dispersive X-ray spectroscopy. It was determined that presence of Nb produces Nb2O5, which is not a protective scale. It also enhances formation MoO3 needles and platelets and amorphous SiO2 on the sample surface as oxidation byproduct none of which forms a protective layer. Consequently, Nb is not an effective agent for prevention of pesting in MoSi2