Surface strengthening and toughening of Si3N4/TiC layered composite by slip casting

Layered composite using monolithic Si3N4 as outer layers and Si3N4-15v/o Ti C as inner core was fabricated by slip casting and pressureless sintering. As the composite is cooled from high sintering temperature, the difference in coefficients of thermal expansion between the constrained inner core and outer layer is expected to establish a compressive surface stress. The exi stence of this residual stress was verified by theoretical analysis and Vic ker's indentation for the samples with various outer layer thickness. The l ayered composites exhibited greater strength, apparent fracture toughness a nd damage resistance due to the presence of compressive surface stresses in the layer. (C) 2000 Kluwer Academic Publishers.