Tailoring the intergranular phases in silicon nitride for improved toughness Page: 4 of 8
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Table 1. Compositions and processing conditions of the (3-Si3N4-whisker/oxynitride-glass
System Composition (eq.%) Temp. Time at Temp.
Si Al Y or RE O N ( C) (min.)
AIY20-I 55 25 20 80 20 1700 6
YA20-I 55 10 35 80 20 1700 8
A1Y20-II 55 25 20 80 20 1600* 60*
YAl20-II 55 10 35 80 20 1600* 60*
LaAL 50 25 25 67 33 1680 30
La 57 0 43 79 21 1700 4
*A1Y20-II and YAl20-II were obtained by annealing AIY20-I and YAL20-I under these
(a) (b) 8 l s*
a) 3~-Si3N4 b 7
Cracks in Glass o 20 40 6 0 s o
Figure 1. (a) Schematic diagram of the debonding experiment; and (b) data analyses of the
debonding experiment. 0crit can be determined by plotting Idb versus 8.
Seeded silicon nitrides with 2 wt.% f3-Si3N4 single crystal seeds were processed using tape-
casting and gas pressure sintering, following the procedures in Refs. 5-6. Three different Al:Y
ratios were studied: 3:2, 1:1 and 1:3 in eq.% (i.e. A1203:Y203 ratios: 2.8:4, 2:5 and 1:6.25 in
wt.%). A fine-grain silicon nitride without seeds was also prepared as a reference. The
microstructure of the materials was characterized using scanning electron microscopy (SEM)
and transmission electron microscopy (TEM). Composition analyses of the microstructures
were conducted using energy dispersive x-ray spectrometry (EDS) in the SEM and TEM. The
R-curve response of the seeded/un-seeded silicon nitrides was investigated using an applied
moment double cantilever beam (DCB) geometry with the crack plane oriented both
perpendicular and parallel to the tape-casting direction. The DCB sample was precracked with
an initial crack length between 50-200 m. Details on the testing module and sample prepara-
tion can be found in Ref. 7. During the experiments, the testing stage was placed either in the
chamber of an SEM or on the stage of an optical microscope for direct observation of crack
interacting with microstructures.
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Sun, E. Y.; Becher, P. F.; Plucknett, K. P.; Waters, S. B.; Hirao, K. & Brito, M. E. Tailoring the intergranular phases in silicon nitride for improved toughness, article, December 31, 1996; Tennessee. (digital.library.unt.edu/ark:/67531/metadc677714/m1/4/: accessed November 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.