Effect of minor alloying with Al on oxidation behaviour of MoSi2 at 1200°C

Abstract

Abstract Effect of Al alloying in small concentrations on oxidation behaviour of molybdenum di-silicide (MoSi 2 ) at 1200°C has been investigated. MoSi 2 –2.8 and 5.5 at.% Al alloys possessed 0.5, and 2.5 at.% Al in solid solution, respectively, and dispersoids of α -Al 2 O 3 . On the other hand, MoSi 2 –9 at.% Al alloy possessed 3.1 at.% in solid solution in MoSi 2 and Mo(Si,Al) 2 phase, besides α -Al 2 O 3 dispersoids. The kinetics of oxidation of all the alloys followed a parabolic rate law. The oxidation rate was higher in the MoSi 2 –Al alloys in comparison to MoSi 2 , with weight gain values varying by an order of magnitude. The MoSi 2 –5.5 and 9 at.% alloys demonstrated closely related oxidation characteristics and proved to be more resistant to oxidation than MoSi 2 –2.8 at.% Al alloy. The oxide scale comprised of SiO 2 in MoSi 2 , mixture of SiO 2 and α -Al 2 O 3 in MoSi 2 –2.8 at.% Al alloy, and α -Al 2 O 3 in case of MoSi 2 –5.5 and 9 at.% Al alloys. The mechanism of oxidation has been analysed using thermodynamic and kinetic considerations.