Microstructure/mechanical-property relationships and R-curve behavior in Si(sub 3)N(sub 4)/Si(sub 3)N(sub 4)(w) composites

摘要

Fracture toughness of Si(sub 3)N(sub 4)-whisker-reinforced Si(sub 3)N(sub 4)-matrix composites were evaluated with various whisker contents. Toughness was observed to increase with increasing whisker content, reaching a maximum value of 8.8 MPa(radical)4 at 5 vol.% whisker content. Additional whisker content caused reduced toughness. A model based on microstructural features indicates that the observed dependence of toughness on whisker content is due to both whisker-toughening and matrix-grain-size effects. Composites with 5 vol.% whisker content showed a rising crack growth resistance (R-curve) behavior. This is believed to be a combined effect of crack bridging and crack deflection due to both elongated grains and reinforcing whiskers.