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

Silicon nitride (Si 3 N 4 ) ceramics were fabricated by gas pressure sintering (GPS) using four sintering additives: Y 2 O 3 –MgO, Y 2 O 3 –MgF 2 , YF 3 –MgO, and YF 3 –MgF 2 . The phase composition, grain growth kinetics, mechanical properties, and thermal conductivities of the Si 3 N 4 ceramics were compared. The results indicated that the reduction of YF 3 on SiO 2 , induced a high Y 2 O 3 /SiO 2 secondary phase ratio, which improved the thermal conductivity of the Si 3 N 4 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).