Processing of a Mullite Matrix, Molybdenum Disilicide Reinforced Composite

摘要

A mullite matrix reinforced with molybdenum disilicide particles was investigatedas a potential high temperature composite material. Mullite is well known for its high temperature strength, creep resistance, corrosion resistance and ability to withstand oxidizing environments. MoSi2 has the potential to be a good reinforcement because: it forms a protective silica layer during oxidation, undergoes a brittle to ductile transformation at 900-1000C which would increase high temperature composite toughness, and is thermodynamically stable with mullite. Samples containing 2.5 to 20 vol% MoSi2 were processed using both hot pressing and pressureless sintering techniques. Low temperature mechanical testing was performed both in the as sintered state and after oxidation at 1400 C for 96 hours. Densities of greater than 93% of theoretical were attained for composites containing up to 20 vol% MoSi2 via pressureless sintering. K(sub Ic) and strength values of the as-sintered composite were up to two times that of monolithic mullite. After oxidation at 1400 C for 96 hours, strength improved by 1.5 times over the as-sintered strength, and fracture toughness improved by 2.5 times over the as-sintered toughness indicating that the composite is self-healing during oxidation.