MECHANISM OF HARDENING OF A PRESSURE-SINTERED MATERIAL
BASED ON A SiC–C SOLID SOLUTION
N. F. Gadzyra,
G. G. Gnesin,
and A. A. Mikhailik
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 1, pp. 13 – 17, January, 2001.
The kinetics of sintering of a powdered solid solution of carbon in silicon carbide sintered under a high pres
sure is considered. The role of diamond-like carbon clusters in the structure of silicon carbide in the process of
structure formation is determined. It is shown that the parameters of the microstructure of sintered ceramics
based on a SiC–C solid solution are correlated with its hardness.
Powdered solid solution of carbon in silicon carbide dif-
fers from standard commercial silicon carbide powders of
cubic modification available in the world market by a lower
lattice parameter. For the first time such a powder was syn-
thesized by the method of self-propagating high-temperature
synthesis (SHS) with thermally expanded graphite as the car-
bon component . The reduction of the lattice parameter is
caused by partial substitution of silicon positions by carbon
atoms (formation of an anti-size structure), which leads to
the formation of diamond-like carbon clusters hardening the
SiC structure [2 – 5].
In accordance with the model of the solid solution of car
bon in SiC , carbon clusters in a structure of cubic modifi
cation have the form of planar defects that create micro
stresses. This feature of the structure of silicon carbide pow
der increases the nonequilibrium and provides a high sinter
ability, chiefly due to change in the atomic surroundings both
inside the clusters and on their coherent boundaries with the
Si matrix .
The present work is devoted to an analysis of micro
structural characteristics and mechanical properties of SiC–C
ceramics sintered at high pressure and temperature and the
choice of optimum sintering conditions for providing en
hanced mechanical properties in the novel ceramics.
METHODS OF EXPERIMENT
Powders of the solid solution of carbon in SiC were syn
thesized by the known method . The sintering was per
formed in a DO-044 device for uniaxial compression in a
high-pressure chamber of the “toroid” type at 2 – 8 GPa and
1000 – 1800°C.
The diffractographic study was performed in a
DRON-UM1 diffractometer (monochromatic Cu K
tion, 0.05° scanning step, 120-sec exposition at every point).
The approximation of the diffraction profiles, the lattice peri-
ods, and the structural computation were performed using the
CSD software . The Raman spectra were detected with the
help of a Jobin-Yvon U-1000 spectrometer. The electron mi-
croscopic study was performed using a PEMU-125 micro-
scope. The changes in the density of the sintered specimens
were measured by the method of hydrostatic weighing. The
hardness was determined by the Vickers method in a stan
dard TP-73-1 machine under a load of 2 kg on the diamond
DISCUSSION OF RESULTS
The particles of the powder SiC–C solid solution have
nonuniform sizes. The mean grain size fluctuates within a
rather wide range of 0.05 – 0.35 mm. The chief feature of the
image of some of the grains is a specific striped contrast due
to packing defects and the presence of numerous microtwins.
The planar defects represented by extended carbon clusters
in the SiC structure generate a like striped contrast on the
electron microscopic images and therefore can hardly be ob
A special feature of the Raman spectra of the studied
powder is the presence of a carbon peak in addition to that of
SiC and caused by the disorder of the structure. However, the
smeared nature of the peak can be a result of the integration
of several peaks due to various structural states of carbon.
Refractories and Industrial Ceramics Vol. 42, Nos.1–2, 2001
1083-4877/01/0102-0011$25.00 © 2001 Plenum Publishing Corporation
Institute for Problems of Materials Sciences of the National
Academy of Sciences of Ukraine, Kharkov, Ukraine.