Synergistic effect of binary fluoride sintering additives on the properties of silicon nitride ceramics

A variety of combinations of YF 3 and MgF 2 were used as sintering aids in the fabrication of Si 3 N 4 ceramics via gas pressure sintering (GPS). The synergistic effects of YF 3 and MgF 2 on the liquid viscosity, mechanical properties, thermal conductivities, and grain growth kinetics of the Si 3 N 4 ceramics were investigated. The results showed that appropriately adjusting the YF 3 /MgF 2 ratio could decrease liquid viscosity, reducing the diffusion energy barrier of the solute atom and promoting mass transfer. Meanwhile, the chemical bonding strength in the grain boundary complexions formed by the metal cations also influenced grain boundary migration. Samples doped with 4 mol% YF 3 and 2 mol% MgF 2 achieved the lowest grain growth exponent ( n = 2.9) and growth activation energy ( Q = 616.7 ± 16.5 kJ mol −1 ) as well as the highest thermal conductivity (83 W m −1 K −1 ) and fracture toughness (8.82 ± 0.13 MPa m 1/2 ).