Fabrication of multilaminated Si₃N₄-Si₃N₄/TiN composites and its anisotropic fracture behavior

Laminated composites containing alternate layers of Si₃N₄ and TiN/Si₃N₄ materials were used as model material for investigating the crack behaviors and mechanical properties. Results indicated that both strength and toughness in laminated composites were higher than that of monolithic silicon nitride. The failure profiles were affected by the stored strain energy prior to failure and the stress gradient in each layer. Cracks deviated successively from one layer to the other due to periodic stress distribution. Samples with better strength and toughness also had a longer crack propagation path and higher amplitude of crack deviation. The periodic stress distribution in laminated composites was confirmed by the measurements of indentation crack length. Results also suggested a tensile stress in the Si₃N₄ layer and compressive stress in the TiN/Si₃N₄ layer, in directions normal to the free sample interface.