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Evolution of Microstructure and Intergranular Glass Chemistry in Plastically Deformed Nanocrystalline Si 3 N 4 Ceramics
Author(s) -
Wananuruksawong Raayaa,
Shinoda Yutaka,
Akatsu Takashi,
Wakai Fumihiro
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.13259
Subject(s) - intergranular corrosion , materials science , superplasticity , nanocrystalline material , microstructure , grain growth , phase (matter) , deformation (meteorology) , flow stress , stress (linguistics) , elongation , metallurgy , mineralogy , composite material , chemistry , nanotechnology , ultimate tensile strength , linguistics , philosophy , organic chemistry
Nanograined Si 3 N 4 ceramics with Y 2 O 3 – Al 2 O 3 – MgO as sintering additive exhibited superplastic elongation of >300% at 1923 K with an initial strain rate of 5 × 10 −4 s −1 . Flow stress was less than 4 MPa up to elongation of 130%. In the later stage of deformation, the flow stress increased with strain due to the grain growth and the alignment of elongated grains. The volume fraction of glassy phase significantly reduced due to vaporization of glassy phase. The chemical analysis by TEM / EDS revealed that the chemical composition of the near Si 3 N 4 grain surface was different from that of the interior of the glass pocket at multigrain junctions due to absorption of additive cations on the Si 3 N 4 grain. The chemistry of intergranular glassy phase changed significantly in the later stage of deformation accompanying the microstructural evolution. It is suggested that the flow stress, which depends on the viscosity of intergranular glassy phase, varies with the change in glass chemistry during deformation.