Long-term oxidation behavior of in situ synthesized SiC particulate-reinforced MoSi2 matrix composites at 900℃

MoSi2 intermetallic is well known as one of the most promising compounds used as structural components due to its high melting point, relatively low density, excellent oxidation resistance, and good strength at high temperatures. Unfortunately, MoSi2 has poor toughness at low temperatures and low creep strength at elevated temperatures. Especially, MoSi2 alloy usually exhibits severe "pest oxidation" at low temperatures of between 400 and 900℃. These problems limit the applications of MoSi2 alloys. The main methods to solve these problems are alloying and compounding. Unfortunately, so far, the problem of low-temperature oxidation resistance of MoSi2 has not been completely solved, and its composite materials are reinforced using external means. In a previous work, SiC particle-reinforced MoSi2 matrix composites were prepared by an in situ synthesis technique, and the microstructures and the mechanical behaviors at room temperature and high temperature were systematically studied. In this work, the long-term oxidation behavior of in situ synthesized SiC particulate-reinforced MoSi2 matrix composites with different volume fractions and occurring at 900℃ for 1000 h was investigated. The composites are not observed to disintegrate (pest) after oxidation for 1000 h. The oxidation resistances of six kinds of materials appear excellent. The composite synthesized by in situ possesses higher oxidation resistance than the traditional composite, which is fabricated by hot-pressing the mixture of commercial powders of MoSi2 and SiC. The surface of scales consists of α-SiO2 (α-quartz), and the subsurface is composed of Mo5Si3. The oxidation of the composites is conducted not only between MoSi2 and O2, but also SiC is oxidized. Selective oxidation of Si completely takes place at 900℃. This selective oxidation results in the spontaneously formation of a layer of dense SiO2 protective scale on the MoSi2 surface, making the material exhibit excellent long-term oxidation resistance.