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Intergranular Nanostructure Effects on Strength and Toughness of Si 3 N 4
Author(s) -
Mikijelj Biljana,
Nawaz Zubair,
Kruzic Jamie J.,
Idrobo Juan,
Swab Jeffrey J.,
Özcoban Husseyin,
Jelitto Hans,
Schneider Gerold A.,
Fett Theo,
Liu Yi
Publication year - 2015
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.13484
Subject(s) - materials science , intergranular corrosion , microstructure , ionic radius , dopant , toughness , doping , composite material , mineralogy , ion , chemistry , optoelectronics , organic chemistry
Strength, toughness, microstructure, and atomic adsorption arrangement in silicon nitrides with MgO and RE 2 O 3 additions ( RE = La, Gd, Y, Lu) were examined. Mechanical properties were high for La, Gd, and equal La–Lu additions, but surprisingly were progressively lower for Y‐ and Lu‐doped samples. The lower strength and toughness were associated with fewer visible crack deflections and grain bridges. Detailed microstructural analysis of the Lu‐doped material revealed a complex intergranular nanostructure with variable Lu content and Si 3 N 4 nanocrystals. Furthermore, the Lu‐rich areas showed an extra Lu‐adsorption site on the Si 3 N 4 prismatic planes not previously observed in other studies. This inhomogeneous structure was attributed to grain growth impingement and higher viscosity of the Lu‐doped oxynitride glass that slows homogenization. The Y‐doped material with nearly identical glass viscosity demonstrates intermediate behavior. Finally, substituting half of the Lu 2 O 3 with La 2 O 3 resulted in a homogenous intergranular structure, attributed to a lower viscosity of the oxynitride glass phase, and high mechanical properties. Overall, care must be taken when adapting Si 3 N 4 processing parameters for the smaller ionic radius rare earth dopants such as Lu and Y.