Microstructure and Selected Properties of Si3N4

The effects of strengthening phase in particulate ceramic composites on their properties were studied in presented paper. The experimental materials were a monolithic Si3N4 and particulate ceramic composites consisting of Si3N4 matrix with different additions of the SiC strengthening phase (10 and 20 vol.%). The microstructure, density, hardness and fracture toughness of Si3N4 + SiC ceramic composite materials were compared with monolithic Si3N4 based ceramic material. The addition of SiC particles into the Si3N4 based matrix does not positively influence the phase transformation from alpha-Si3N4 to beta-Si3N4 in Si3N4 + SiC ceramic composite materials, but it affects the growth of prismatic beta-Si3N4 grains and contributes to the creation of fine-grained microstructure. The increase of SiC strengthening phase portion slightly increases relative density of Si3N4 + SiC ceramic composite materials. The hardness of ceramic materials increased from 14.48 GPa at monolithic Si3N4 ceramics to 16.99 GPa at ceramic composite with 20 vol.% SiC. The highest fracture toughness value of 8.30 MPa.m(1/2) was achieved for monolithic Si3N4 ceramics, the lowest value of 7.09 MPa.m(1/2) was achieved for ceramic composite with 20 vol.% SiC.