Fabrication of bimodal nanomodified TaN–Si3N4–SiAlON ceramics with enhanced fracture toughness and wear resistance by self-propagating high-temperature synthesis and hot pressing
The effect of dispersed hexagonal boron nitride, reduced graphene oxide, and single-walled carbon nanotubes additives on the microstructure, physical, mechanical, and tribological properties of nanomodified TaN–Si 3 N 4 –SiAlON ceramics was investigated. Disk-shaped ceramic samples were fabricated by self-propagating high-temperature synthesis (SHS) followed by hot pressing (HP) at 1600 °C under a pressure of 35 MPa. Their microstructure and phase composition were examined using X -ray diffraction, scanning and transmission electron microscopy, and Raman spectroscopy. The results showed that, under hot-pressing conditions, no chemical interaction was occurred between the dispersed additives and the components of the TaN–Si 3 N 4 –Ta 5 Si 3 –YAG SHS reaction mixtures. The ceramics had a microstructure consisting of polyhedral h -TaN/ c -TaN grains approximately 3 µm in size, surrounded by submicron Si 3 N 4 grains. The introduction of dispersed additives increased the hardness till 8.8 GPa and fracture toughness till 9.5 MPa·m 1/2 , while the flexural strength remained within 430–484 MPa and the thermal conductivity within 13.2–13.5 W/(m·K). Tribological tests under dry sliding conditions showed that the addition of carbon nanotubes reduced the specific wear rate to 7.08·10 –6 mm 3 /(N·m). This effect was attributed to the suppression of grain growth during hot pressing and the formation of oxidized wear products based on Ta 2 O 5 .