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Observations on the Influence of Secondary Me Oxide Additives (Me=Si, Al, Mg) on the Microstructural Evolution and Mechanical Behavior of Silicon Nitride Ceramics Containing RE 2 O 3 (RE=La, Gd, Lu)
Author(s) -
Becher Paul F.,
Shibata Naoya,
Painter Gayle S.,
Averill Frank,
Van Benthem Klaus,
Lin HuaTay,
Waters Shirley B.
Publication year - 2010
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/j.1551-2916.2009.03435.x
Subject(s) - microstructure , materials science , intergranular corrosion , silicon nitride , phase (matter) , ceramic , chemical engineering , transmission electron microscopy , adsorption , nitride , metallurgy , silicon , mineralogy , composite material , nanotechnology , layer (electronics) , chemistry , organic chemistry , engineering
The evolution of β‐Si 3 N 4 microstructures is influenced by the adsorption of rare earth (RE) elements at grain surfaces and by the viscosity of the intergranular phases. Theoretical and scanning transmission electron microscopy studies show that the RE atoms exhibit different tendencies to segregate from the liquid phase to grain surfaces and different binding strengths at these surfaces. When combined with MgO (or Al 2 O 3 ) secondary additions, the rare earth additives are combined in low‐viscosity intergranular phases during densification and the α‐ to β‐phase transformation and microstructural evolution are dominated by the RE adsorption behavior. On the other hand, a much higher viscosity intergranular phase forms when the RE 2 O 3 are combined with SiO 2 . While the RE adsorption behavior remains the same, phase transformation and microstructure are now dominated by Si 3 N 4 solubility and transport in the high liquid phase. By understanding these additive effects, one can develop reinforced microstructures leading silicon nitride ceramics with greatly improved mechanical behavior.