Effect of porous Si3N4 preform on the mechanical properties of Si3N4/Al composites with interpenetrating network structure

Abstract Si 3 N 4 /Al composites with three-dimensional interpenetrating network structures were fabricated by direct squeeze casting AlSi12 melt into the open porous Si 3 N 4 preforms, which were synthesized by pressureless sintering method using different sintering additives. The effect of the sintering additive (Y 2 O 3 and Re 2 O 3 [Re=La, Gd, Er]) on the microstructure and mechanical properties of the porous Si 3 N 4 preforms and the final MMCs were investigated. The SN–La samples with porosity ~38% showed the highest flexural strength of 263 MPa and the highest fracture toughness of 4.3 MPa·m 1/2 , due to the bimodal microstructure in which some large elongated β-Si 3 N 4 grains with high aspect ratio were embedded in the fine matrix grains. The results showed that the Si 3 N 4 preform had a significant impact on the mechanical properties of the composites. The strongest Si 3 N 4 preform led to the highest strength of the infiltrated sample SNA–La composite (562 MPa) because the load was transferred from the aluminum matrix to the β-Si 3 N 4 grains. Although the fracture toughness of K IC of Si 3 N 4 preforms was quite different, the K IC of Si 3 N 4 /Al composites was increased slightly from 5.2 to 6.0 MPa·m 1/2 . It was because the interfacial characteristics between elongated Si 3 N 4 grains and infiltrated Al phase of the composites were similar.