TY - JOUR
T1 - SiAlON bulk glasses and their role in silicon nitride grain boundaries
T2 - Composition-structure-property relationships
AU - Hampshire, Stuart
AU - Pomeroy, Michael J.
PY - 2012/7
Y1 - 2012/7
N2 - SiAlON glasses are silicates or alumino-silicates, containing Mg, Ca, Y or rare earth (RE) ions as modifiers, in which nitrogen atoms substitute for oxygen atoms in the glass network. These glasses are found as intergranular films and at triple point junctions in silicon nitride ceramics and these grain boundary phases affect their fracture behaviour. This paper provides an overview of the preparation of M-SiAlON glasses and outlines the effects of composition on properties. As nitrogen substitutes for oxygen in SiAlON glasses, increases are observed in glass transition temperatures, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of grain boundary glass chemistry in silicon nitride ceramics. Oxide sintering additives provide conditions for liquid phase sintering, reacting with surface silica on the Si 3N 4 particles and some of the nitride to form SiAlON liquid phases which on cooling remain as intergranular glasses. Thermal expansion mismatch between the grain boundary glass and the silicon nitride causes residual stresses in the material which can be determined from bulk SiAlON glass properties. The tensile residual stresses in the glass phase increase with increasing Y:Al ratio and this correlates with increasing fracture toughness as a result of easier debonding at the glass/β-Si 3N 4 interface.
AB - SiAlON glasses are silicates or alumino-silicates, containing Mg, Ca, Y or rare earth (RE) ions as modifiers, in which nitrogen atoms substitute for oxygen atoms in the glass network. These glasses are found as intergranular films and at triple point junctions in silicon nitride ceramics and these grain boundary phases affect their fracture behaviour. This paper provides an overview of the preparation of M-SiAlON glasses and outlines the effects of composition on properties. As nitrogen substitutes for oxygen in SiAlON glasses, increases are observed in glass transition temperatures, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of grain boundary glass chemistry in silicon nitride ceramics. Oxide sintering additives provide conditions for liquid phase sintering, reacting with surface silica on the Si 3N 4 particles and some of the nitride to form SiAlON liquid phases which on cooling remain as intergranular glasses. Thermal expansion mismatch between the grain boundary glass and the silicon nitride causes residual stresses in the material which can be determined from bulk SiAlON glass properties. The tensile residual stresses in the glass phase increase with increasing Y:Al ratio and this correlates with increasing fracture toughness as a result of easier debonding at the glass/β-Si 3N 4 interface.
KW - Fracture resistance
KW - Grain boundary
KW - Oxynitride glasses
KW - Residual stress
KW - Silicon nitride
KW - Sintering additives
KW - Thermal expansion mismatch
UR - http://www.scopus.com/inward/record.url?scp=84865422484&partnerID=8YFLogxK
U2 - 10.4191/kcers.2012.49.4.301
DO - 10.4191/kcers.2012.49.4.301
M3 - Article
AN - SCOPUS:84865422484
SN - 1229-7801
VL - 49
SP - 301
EP - 307
JO - Journal of the Korean Ceramic Society
JF - Journal of the Korean Ceramic Society
IS - 4
ER -