Specifics of structure formation and properties of composite ceramics in the Si3N4 — Al2O3 system

Abstract

An investigation of the performance characteristics of silicon nitride ceramics due to the introduction of hollow and solid microspheres of aluminum oxide is continued. The highest fracture toughnessKIc, equal to 4.5 MPa · m1/2, for the same ultimate bending strength of 300 – 500 MPa is attained in a ceramics based on an SHS matrix with hollow microspheres. This is associated with inhomogeneities of the microstructure, namely, the presence of coarse spherical pores and elongated prismatic grains that can hamper the propagation of cracks and thus affect considerably the fracture toughness. This material possesses a maximum fraction of closed pores and is lighter than its analogs. The use of microspheres of Al2O3 as pore-forming structural cells decreases the density of the material by 5 – 10%. The efficiency of the developed composite materials is shown by tests of armor plates.