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.