Příprava a charakteristika kompozitů Si3N4 + MgSiN2

Abstract

Silicon nitride-based ceramic materials have excellent mechanical and thermo-physical properties, however with limited industrial applications. This work describes the preparation of new ceramic composite based on Si3N4 and ternary MgSiN2 in a content from 10% up to 80% by gas pressure sintering (GPS) and hot-pressing (HP). The nitridation and sintering conditions were optimized in both types of densification. Some of the mechanical properties like hardness, indentation fracture toughness and strength were evaluated. The hardness of gas pressure sintered composites was in the range of 8.2 – 15.5 GPa, while the hot pressed samples reached a hardness of 15.5 – 16.5 GPa. The indentation fracture toughness was around 5 – 8 MPa•m1/2, depending on the content of elongated -Si3N4 grains and porosity. The bending strength was in the range of 420 – 830 MPa. The mechanical properties were discussed by means of phase composition and microstructure. Except of mechanical properties also the thermal conductivity of composites was determined. The highest thermal conductivity was obtained for the composites containing 5% of MgSiN2; 41 Wm-1K-1 for the as hot-pressed composite and 129 Wm-1K-1 for the annealed composite. These excellent mechanical properties and very high thermal conductivity allows the application of Si3N4-MgSiN2 composites in severe industrial applications and in electrotechnics.