Si

3

N

4

ceramics with high thermal conductivity and high strength were fabricated through gas pressure sintering at 1 MPa N

2

and 1850 ℃

holding for 4 h in this study. Effects of doping methods (coating and traditional ballmilling) and sintering additive content on the phase composition

relative density

microstructure

mechanical property and thermal conductivity of the as-prepared Si

3

N

4

ceramics were systematically studied. The results show that increasing the sintering additive content enhances the second-phase crystallinity

relative density

mechanical property

and thermal conductivity of the Si

3

N

4

ceramics. Compared with the traditional ball-milling method introducing sintering additives

the coating method is more favorable to improving the dispersion uniformity of sintering additive

enabling Si

3

N

4

ceramics to form a continuous network liquid phase with sintering additive mass fraction of merely 3%

thereby promoting the densification

improving microstructure uniformity

and ultimately enhancing the mechanical property and thermal conductivity of Si

3

N

4

ceramics. The sample prepared using the coating method with sintering additive mass fraction of 5% achieved a thermal conductivity of 76.07 W·m

–1

·K

–1

fracture toughness of 8.39 MPa·m

1/2

and bending strength of 922.41 MPa

and showing a 13% increase in bending strength compared with the ball-milled sample.