Oxidation behavior of Mo–12.5Si–25B alloy at high temperature

Abstract

The cyclic oxidation kinetics of arc-melted Mo–12.5Si–25B alloy exposed at high temperature has been studied. Oxide scale cross-sectional microstructures of Mo–12.5Si–25B alloy oxidized at 1200 °C for 10 min, 2 h and 100 h have been investigated. The cyclic oxidation kinetics data exhibits initial rapid mass loss followed by slow mass loss. When exposed for 10 min, a discontinuous, irregular thin scale is formed and the scale consists mainly of crystalline and amorphous SiO 2. When exposed for 2 h, a continuous about 20 μm thick scale containing many pores is formed. The matrix of the scale is amorphous SiO 2 and the dispersion is MoO 2. It is also found that there is a Mo solid solution (Mo(ss)) interlayer between the scale and the substrate. After oxidation for 100 h, the approximately 110 μm thick scale is formed and the scale is continuous and dense. The scale is composed primarily of amorphous SiO 2 including MoO 2 dispersions. At the scale/substrate interface, the regions containing the three-phase Mo–Mo 5SiB 2 (T2)–Mo 3Si eutectic are the preferential oxidation sites for 10 min and 2 h exposure, the preferentially oxidized products are SiO 2 and Mo–Si–O oxide. For 100 h exposure the Mo 3Si is preferentially oxidized in the Mo–T2–Mo 3Si eutectic, leaving unoxidized T2 and Mo.