Dense Si3N4 BN composite ceramics were fabricated by spark plasma sintering at 1 500,1 600 and 1 650 ℃ under 50 MPa for 5 min using Si3N4 and BN powders as starting materials and 2 mass% Al2O3 and 6 mass% Y2O3 as sintering additives. The volume fraction of BN in Si3N4 BN composite powders was chosen as 10% ,20% ,and 30% ,respectively. The results of XRD and SEM show that α-Si3N4 completely turns into β-Si3N4 when the composite ceramics are sintered at 1 650 ℃ ; the addition of BN hinders the growth of Si3N4 grains,refining the structure; Vickers hardness and fracture toughness of the composite ceramics decrease with the increase of BN content.
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