Abrasive wear of Si3N4-MoSi2 composites

Molybdenum disilicide (MoSi2) particles have been added to silicon nitride (Si3N4) to form ceramic matrix-intermetallic composites. Benefits associated with the addition of the MoSi2 to Si3N4 include higher strength, higher fracture toughness, no loss in oxidation resistance, and lower electrical resistivity. However, since the hardness of MoSi2 is approximately half that of Si3N4, a significant decrease in the specific wear rate of the Si3N4-MoSi2 composites is expected to result from the incorporation of the MoSi2 in the Si3N4. In this study, it was found, however, that the wear resistance of Si3N4 improves slightly or is unaffected by additions of small volume fractions (less than or equal to 20%) of MoSi2 particles, during two-body abrasion by SiC particles. At higher volume fractions, the Si3N4-MoSi2 composites wear at rates no greater than 1.5 times that of monolithic Si3N4. The volume wear of the composites was dependent on composite hardness, fracture toughness and microstructural features (i.e. MoSi2 particle size). Given equivalent hardness and fracture toughness for a composite pair at the same volume fraction, however, the composite with the smaller MoSi2 particles exhibited the lower wear rate. The abrasive wear behavior of the Si3N4-MoSi2 composites can be described in terms of the inverse rule of mixtures for composites.