Cm. Huang et al., COMBUSTION-SYNTHESIZED BETA'-SIALON REINFORCED WITH SIC MONOFILAMENTS, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 188(1-2), 1994, pp. 341-351
Dense composites of combustion-synthesized beta'-Si3Al3O3N5 (beta'-SiA
lON) reinforced with 20 vol.% SIC monofilaments (AVCO SCS-6) were hot
pressed at a temperature of 1600 degrees C for 2 h under a pressure of
34 MPa. The mechanical properties of as-fabricated composites were in
vestigated in the three-point flexure mode. The composites exhibited s
ignificant improvement in the work of fracture as well as in the ultim
ate strength, in comparison with monolithic beta'-SiAlON. Ultimate fle
xure strength values between 682 and 793 MPa for the composite and bet
ween 398 and 528 MPa for the monolithic beta'-SiAlON were obtained. A
work of fracture of 13-20 kJ m(-2) was obtained for the composite, com
pared with 1.7-3.1 kT m(-2) for the monolithic material. Optical micro
scopy and scanning electron microscopy (SEM) examinations of the fract
ured specimens showed the usual composite toughening mechanisms of mic
rocracking, interfacial debonding, filament bridging and pull-out. The
interfacial shear strength as well as frictional stress were also inv
estigated with a fiber push-out technique. The push-out load-deflectio
n curves revealed a moderate interfacial bonding strength of 26 MPa an
d a frictional sliding stress of 24 MPa. Transmission electron microsc
opy interfacial characterization was correlated with SEM observation o
f the interfacial debonding site. It revealed the presence of definite
but weak physical bonding between the outermost carbon-rich layer of
the SiC filament and the matrix. It appeared that the filament and the
matrix were compatible with each other both physically and chemically
, despite the fact that the matrix contained 20 wt.% Al2O3 as a second
ary phase.