Densification and microstructure of Si3N4-TiN ceramic composites

Abstract

Silicon nitride is a ceramic material widely used in various structural applications at high temperatures owing to its excellent combination of mechanical and thermal properties. To increase the application of Si 3 N 4 , many researches have been developed to improve its fracture toughness and processing conditions. In this study, the sintering and microstructure of Si 3 N 4-TiN composites, containing Al 2 O 3 and Y 2 O 3 as sintering aids, were studied. Samples were obtained by the conventional method of mixing powders and sintered at 1750 ºC/1 h and 1815 ºC/1 h under nitrogen atmosphere. Density values of the samples were determined by the Archimedes method, reaching values between 96.9% and 98.0% of theoretical density, with a porosity of less than 0.5%. The sintered samples were analyzed by X-ray powder diffraction and scanning electron microscopy. The results showed the materials reached high fracture toughness, low hardness and a microstructure with TiN grains dispersed in a β-Si 3 N 4 matrix containing an amorphous intergranular phase.

Oxidation behavior of Si3N4-TiN composites at 1400 oC

“…Aluminum cations in the amorphous phase come from the intergranular phase of the sintered composites. Before the oxidation tests, aluminum cations are present in the intergranular phase of Si 3 N 4 -TiN composites as a result of cooling of the liquid phase during the sintering process due to the reaction between the additives (Al 2 O 3 and Y 2 O 3 ) with silica (SiO 2 ) on the surface of the Si 3 N 4 particles, as described in our previous work 26 .…”

A study on fabrication of silicon nitride-based advanced ceramic composite materials via spark plasma sintering

“…Also, relative densities of the sintered samples ranged from 96.9% to 98% as calculated from the Archimedes method. 98 Yang et al reported that the microstructure of b-Si 3 N 4 ceramics can be controlled by adding b-Si 3 N 4 nuclei through SPS at 1650 C for 5 min and post-sintering heat treatment at 1900 C for 4 h. They also showed how the thermal conductivity of b-Si 3 N 4 can be tailored by controlling the microstructure. In this way, they were able to achieve a maximum thermal conductivity value of the order of 84.6 W m À1 K À1 .…”