Thermal conductivity and mechanical properties of Si3N4 ceramics with binary fluoride sintering additives

Silicon nitride (Si3N4) ceramics were fabricated by gas pressure sintering (GPS) using four sintering additives: Y2O3-MgO, Y2O3-MgE2, YF3-MgO, and YF3-MgF2. The phase composition, grain growth kinetics, mechanical properties, and thermal conductivities of the Si3N4 ceramics were compared. The results indicated that the reduction of YF3 on SiO2, induced a high Y2O3/SiO2 secondary phase ratio, which improved the thermal conductivity of the Si3N4 ceramics. The depolymerization of F atom reduces the diffusion energy barrier of solute atom and weakens the viscous resistance of anion group, which was beneficial to grain boundary migration. Besides exhibiting a lower grain growth exponent(n = 2.5)and growth activation energy (Q = 587.94 +/- 15.35 kJ/mol), samples doped with binary fluorides showed excellent properties, including appreciable thermal conductivity (69 W m(-1) K-1), hardness (14.63 +/- 0.12 GPa), and fracture toughness (8.75 +/- 0.18 MPa m 1/2), as well as desirable bending strength (751 +/- 14 MPa).

Automated summary

In this study, silicon nitride ceramics were fabricated using different sintering additives, with samples doped with binary fluorides showing superior thermal conductivity and mechanical properties. The addition of YF3 reduced the grain growth exponent and activation energy, leading to improved properties in the Si3N4 ceramics.