Laminated B4C-SiC ceramics with improved mechanical properties

Novel laminated ceramics based on B 4 C-SiC composite units were fabricated by hot pressing at 1950 °C under 30 MPa. The laminated ceramic has a three-layer “sandwich structure” that generates compressive residual stress in the outer layer. The trend of surface compressive stress with SiC content in B 4 C-SiC laminated composite units was investigated using finite element analysis and Raman spectroscopy. The results show that residual stress in the surface layer of laminated ceramic increases with increasing interlayer compositional differences. The enhancement in bending strength and hardness is attributed to the surface residual compressive stress, which counteracts external loads and retards surface crack propagation, whereas the improved fracture toughness arises from crack growth inhibition by surface compressive stress and crack deflection caused by tensile stress in the intermediate layer. The apparent fracture toughness of laminated ceramic is found to depend on the initial crack length, with maximum toughness achieved when the crack is located at the interface between the outer and intermediate layers. In addition, high compressive stress may induce a greater density of dislocations, which represents a potential toughening mechanism in laminated ceramics. The optimum bending strength, hardness and fracture toughness of the laminated material are 601 ± 28 MPa, 33.6 ± 0.4 GPa and 7.2 ± 0.3 MPa m 1/2 , respectively. The fracture toughness is improved by 51 % compared with the monolithic material. This study demonstrates the simultaneous enhancement of both strength and fracture toughness while maintaining the high hardness of B 4 C ceramics.