Densification and Mechanical Properties of Silicon Nitride Containing Lu 2 O 3 -SiO 2 Additives

Gas pressure sintering (GPS) of reaction bonded silicon nitride (RBSN) was performed using Lu 2 O 3 -SiO 2 additive and the properties were compared with those of specimens prepared using high purity Si 3 N 4 powder. The relative density of RBSN and compacted Si 3 N 4 powder were 68.9 and 47.1%, and total linear shrinkage after sintering at 1900℃ were 14.8 and 42.9%, respectively. High nitrogen partial pressure (5MPa) was required during sintering at 1900℃ in order to prevent the decomposition of the nitride and to promote the formation of SiC. The relative density and 4-point bending strength of RBSN and Si3N4 powder compact were 97.7%, 954MPa and 98.2%, 792MPa, respectively, after sintering at 1900℃. The sintered RBSN also showed high fracture toughness of 9.2MPam 1/2 .

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