Densification of Reaction Bonded Silicon Nitride with the Addition of Fine Si Powder - Effects on the Sinterability and Mechanical Properties

Abstract

The densification behavior and strength of sintered reaction bonded silicon nitrides (SRBSN) that contain Lu 2 O3-SiO 2 additives were improved by the addition of fine Si powder. Dense specimens (relative density: 99.5%) were obtained by gas-pressure sintering (GPS) at 1850oC through the addition of fine Si. In contrast, the densification of conventional specimens did not complete at 1950℃. The fine Si decreased the onset temperature of shrinkage and increased the shrinkage rate because the additive helped the compaction of green bodies and induced the formation of fine Si 3 N 4 particles after nitridation and sintering at and above 1600℃. The amount of residual SiO 2 within the specimens was not strongly affected by adding fine Si powder because most of the SiO 2 layer that had formed on the fine Si particles decomposed during nitridation. The maximum strength and fracture toughness of the specimens were 991 MPa and 8.0 MPa?m 1/2 , respectively.