Microstructure and oxidation response of Mo-Si-B-ZrB2 alloy at 900?C: Effect of pre-oxidation treatment

High temperature oxidation behavior of the Mo-12Si-8.5B-2.5wt%ZrB2 alloy was studied at 900 degrees C and 1300 degrees C in static air, in addition, the oxidation behavior at 900 degrees C after pre-oxidation treatment at 1300 degrees C was inves-tigated. The mass change of the alloy during oxidation at high temperature was in-situ determined by ther-mogravimetry. The oxide layers on the surface of the alloy after oxidation were characterized by XRD, SEM, EDS, XPS and TEM. The results indicated that the alloy oxidized at 900 degrees C exhibited a catastrophic mass loss asso-ciated with the formation of a porous borosilicate scale and continuous escape of MoO3. While the alloy oxidized at 1300 degrees C formed a viscous and protective borosilicate scale, promoting a negligible mass loss during the whole oxidation stage. Application of pre-oxidation treatment at 1300 degrees C appreciably enhanced the oxidation resistance of the alloy at 900 degrees C by decreasing the recession of the alloy. The oxidation kinetic exhibited marginal mass loss during the earlier oxidation stage due to the viscous borosilicate scale provided in advance at 1300 degrees C followed by gradual mass loss resulting from the MoO3-containing borosilicate scale transformation.