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Effect of Aluminum Content on Mechanical Properties and Thermal Conductivities of Sintered Reaction‐Bonded Silicon Nitride
Author(s) -
Kusano Dai,
Hyuga Hideki,
Zhou You,
Hirao Kiyoshi
Publication year - 2013
Publication title -
international journal of applied ceramic technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.4
H-Index - 57
eISSN - 1744-7402
pISSN - 1546-542X
DOI - 10.1111/ijac.12035
Subject(s) - materials science , silicon nitride , nitride , sintering , aluminium , nitriding , impurity , fracture toughness , thermal conductivity , flexural strength , nitrogen , silicon , spark plasma sintering , metallurgy , analytical chemistry (journal) , composite material , layer (electronics) , chemistry , physics , organic chemistry , quantum mechanics , chromatography
A systematic study was conducted of the effect of Al impurities on the mechanical and thermal properties of sintered reaction‐bonded silicon nitrides ( SRBSN s). 2 mol.% Y 2 O 3 and 5 mol.% M g S i N 2 were added as sintering aids to high‐purity raw Si powder, followed by respective additions of 0, 0.01, 0.1, 0.2, and 0.4 mass% of Al relative to Si . The prepared powder mixes were press formed and nitrided in a 0.1 MP a nitrogen atmosphere at 1400°C for 8 h. Postsintering of the nitrides was conducted under a pressurized nitrogen atmosphere of 0.9 MP a at 1900°C for 6 h. The SRBSN specimens exhibited hardly any difference in their four‐point bending strength, which ranged from 800 to 850 MP a. However, their fracture toughness clearly decreased with increasing additive Al content. This is thought to be due to a reduction in the proportion of coarse prismatic grains improving the toughness with increasing additive Al content. A significant reduction in the thermal conductivity was also observed with increasing additive Al content. This is conjectured to be due to the formation of SiAlON through a substituted solid solution of aluminum ( Al ) and oxygen ( O ) in β‐ S i 3 N 4 crystals. An inductively coupled plasma and hot gas extraction method were employed to directly analyze Al and O in β‐ S i 3 N 4 particles. Approximately half of the additive Al was confirmed to be in solid solution in β‐ S i 3 N 4 particles along with the solid solution of O in a chemical formula that nearly corresponds to β‐ S i 6–z A l z O z N 8–z . The chemical analysis results give a Z value range of 0.0006–0.024.