Abrasive wear of Si 3N 4MoSi 2 composites

Abstract

Molybdenum disilicide (MoSi 2) particles have been added to silicon nitride (Si 3N 4) to form ceramic matrix-intermetallic composites. Benefits associated with the addition of the MoSi 2 to Si 3N 4 include higher strength, higher fracture toughness, no loss in oxidation resistance, and lower electrical resistivity. However, since the hardness of MoSi 2 is approximately half that of Si 3N 4, a significant decrease in the specific wear rate of the Si 3N 4MoSi 2 composites is expected to result from the incorporation of the MoSi 2 in the Si 3N 4. In this study, it was found, however, that the wear resistance of Si 3N 4 improves slightly or is unaffected by additions of small volume fractions (≤20%) of MoSi 2 particles, during two-body abrasion by SiC particles. At higher volume fractions, the Si 3N 4MoSi 2 composites wear at rates no greater than 1.5 times that of monolithic Si 3N 4. The volume wear of the composites was dependent on composite hardness, fracture toughness and microstructural features (i.e. MoSi 2 particle size). Given equivalent hardness and fracture toughness for a composite pair at the same volume fraction, however, the composite with the smaller MoSi 2 particle exhibited the lower wear rate. The abrasive wear behavior of the Si 3N 4MoSi 2 composites can be described in terms of the inverse rule of mixtures for composites.