The measurement and characterization of the interfacial toughness of Si3N4/BN composites by a three-point bending test

Abstract In this paper, a simpler method has been proposed for measuring and characterizing the interfacial toughness of Si 3 N 4 /BN composites. A sandwiching material, with one preset crack source connecting directly to a BN interphase in the middle of a single half-Si 3 N 4 matrix, were designed and fabricated by sandwiching a thinner BN layer with two Si 3 N 4 green bodies obtained by die compaction at room temperature. The BN layer had been made by tape casting. The sandwiched sample bars measured with 3×4×50 mm 3 were cut and machined. The interfacial toughness of Si 3 N 4 /BN composites was measured by three-point bending test for pure BN interphase, and interphases modified by different amounts of Si 3 N 4 or Al 2 O 3 . The interfacial toughness values were calculated based on three-point bending fracture mechanics model. The interfacial toughness values we obtained were 38.20, 104.03 and 116.14 J/m 2 for pure BN, BN+15vol.%Si 3 N 4 and BN+25vol.%Si 3 N 4 interphases; 46.86, 53.90, 73.64 J/m2 for BN+16vol.%Al 2 O 3 , BN+36vol.%Al 2 O 3 and BN+63vol.%Al 2 O 3 interphases, respectively. When the amounts of modified Si 3 N 4 or Al 2 O 3 increased, the interphase was strengthened and crack deflection and propagation within interphase could not occur, the interfacial toughness was not obtainable for the corresponding samples, but it could be obtained by extrapolation based on the values obtained in each kind of interphase systems. The results show that the method is simple and effective for measuring and characterizing interfacial toughness, compared with some other related works in literatures.