RETARDATION OF RECRYSTALLIZATION IN THE TiC – SiC SYSTEM
M. I. Podkovyrkin
and V. V. Kartashov
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 8, pp.2–4,August, 2003.
Silicon carbide, introduced into titanium carbide matrix via gas-phase mass transfer and subsequent deposi
tion in the intergranular contact zone, acts as a shield for TiC grains. This results in a sharp retardation of the
collective recrystallization and thus provides a means of controlling formation of the composite ceramic
microstructure under sintering and hot-pressing conditions. By varying the composition and processing pa
rameters in the TiC – SiC system, one can control the microstructure of ceramic materials to optimize their
electrophysical and physicomechanical properties
Understanding of the processes by which the micro
structure of ceramic composites is formed is important for
selecting routes towards optimizing the electrophysical and
physicomechanical properties of these materials. Another
important point to be considered is the grain growth control,
which implies in fact setting a limit to recrystallization pro-
cesses in thermally treated materials (sintering, annealing,
hot pressing, etc.). In technology, an effective means of re-
tarding the accumulative recrystallization of ceramic mix-
tures is the use of modifying additives inert to the material of
the matrix phase.
The modifying efficiency is determined by the interac
tion between the main (matrix) phase and the additive (modi
fier) and by the mechanism of formation of the ceramic ma
terial during thermal treatment. These two factors are primar
ily to be considered in selecting a modifier. The higher ten
dency towards secondary recrystallization is found in high-
melting phases with a metal-like character of the chemical
bond in crystals such as carbides of titanium, zirconium, and
hafnium. In our study, we have selected titanium carbide for
the matrix phase of the composite; the modifying additive
was silicon carbide virtually inert towards titanium car
Silicon carbide used as a retarder of recrystallization has
proved to be more efficient than excessive carbon (graphite).
So, graphite introduced at a concentration of 20 vol.% makes
it possible to reduce the average grain size of matrix in the
composite ceramic “titanium carbide-graphite” by a factor of
2 – 2.5 , whereas silicon carbide added at 20 vol.% allows
the reduction of TiC grain size by a factor of5–7.
These features reflect the specific behavior of silicon car
bide in heat-treated powdered and porous materials at tem
peratures above 2300 K. Under these conditions, silicon car
bide undergoes dissociative evaporation, that is, mass trans-
fer via the gas phase plays a role in the ceramic formation.
Thus, the main transport mechanism involved in the process
of sintering is dissociative evaporation of silicon carbide fol-
lowed by the condensation on the concave surface of the
contact bridge and by the heterodiffusion [4, 5].
To prepare titanium carbide in a compact form, the
high-temperature hot-pressing method was used. The con-
centration of silicon carbide in TiC – SiC composites varies
from 0 to 40 vol.%. Mixtures of commercially pure pow-
dered carbides with a grain size less than 5 mm were prelimi
nary molded by pressing and then sintered at 2300 – 2700 K
and a holding time of 1 to 4 h. The hot pressing was carried
out at 2300 – 2600 K and a holding time of 0.5 h. Specimens
thus prepared were tested by optical and electron spectro
scopies and by a special electric resistance analysis.
Data on the average grain size of TiC matrices with dif
ferent concentration of the modifier are given in Table 1.
Photomicrographs of the ceramic materials are presented
in Fig. 1.
Refractories and Industrial Ceramics Vol. 45, No. 1, 2004
1083-4877/04/4501-0016 © 2004 Plenum Publishing Corporation
Ural State Technical University (UPI), Ekaterinburg, Russia.
TABLE 1. Average Size of Titanium Car
bide Grains in the Materials
SiC content, vol.% TiC linear grain size, mm
75 ± 8
32 ± 5
15 ± 3
9 ± 2
7 ± 2