Microstructure and oxidation behavior of directionally solidified Mo–Mo5SiB2 (T2)–Mo3Si alloys

The microstructure and oxidation behavior of directionally solidified Mo–10Si–14B (at.%) alloys consisting of very coarse Mo–Mo5SiB2 (T2)–Mo3Si phase have been investigated. Oxide scale cross-sectional microstructures of Mo–10Si–14B alloys oxidized at 1200 °C for 10 min, 2 and 100 h have been studied. Cyclic oxidation kinetics data indicates that significant mass loss occurs with increasing temperature until 1200 °C. Compared with the alloy of growth rate of 30 mm/h, the alloy of growth rate of 10 mm/h oxidizes faster at all temperatures. When exposed for 10 min, a discontinuous, irregular oxide scale with large pores is formed, and the scale consists mainly of crystalline and amorphous SiO2. During the initial oxidation, Mo is preferentially oxidized in Mo–T2–Mo3Si. When exposed for 2 h, many cracks occur in the oxide scale. After oxidized for 100 h, the oxide scale is irregular but relatively continuous with small pores and cracks; the scale is composed primarily of crystalline and amorphous SiO2 including Mo and MoO2 dispersions. The poor oxidation resistance of the directionally solidified Mo–10Si–14B alloy has been attributed primarily to the large Mo particles.