Synthesis and reaction mechanism of Ti3SiC2 by mechanical alloying of elemental Ti, Si, and C powders

Article abstract of DOI:10.1111/j.1551-2916.2005.00417.x

Formation of titanium silicon carbide (Ti₃SiC₂) by mechanical alloying (MA) of Ti, Si, and C powders at room temperature was experimentally investigated. A large amount of granules less than 5 mm in size, consisting of Ti₃SiC₂, smaller TiC particles, and other silicides, have been obtained after ball milling for only 1.5 h. The effect of excess Si in the starting powders on the formation of Ti₃SiC ₂ was studied. The formation mechanism of Ti₃SiC ₂ was analyzed. It is believed that a mechanically induced self-propagating reaction is ignited during the MA process. A possible reaction mechanism was proposed to explain the formation of the final products.

Full text of DOI:10.1111/j.1551-2916.2005.00417.x

J. Am. Ceram. Soc., 88 [8] 2092–2098 (2005)
DOI: 10.1111/j.1551-2916.2005.00417.x
ournal
J
Synthesis and Reaction Mechanism of Ti SiC by Mechanical Alloying
3
2
of Elemental Ti, Si, and C Powders
w
Shi-Bo Li and Hong-Xiang Zhai
School of Mechanical and Electronic Control Engineering, Beijing Jiaotong University, Beijing 100044, China
Formation of titanium silicon carbide (Ti SiC ) by mechanical
2
In general, a self-propagating reaction or a combustion reac-
tion can be triggered by MA of the alloy systems with a large
negative heat of formation. The above reaction is also called
a mechanically induced self-propagating reaction (MSR). The
3
alloying (MA) of Ti, Si, and C powders at room temperature
was experimentally investigated. A large amount of granules
less than 5 mm in size, consisting of Ti SiC , smaller TiC par-
3
2
1
7
ticles, and other silicides, have been obtained after ball milling
for only 1.5 h. The effect of excess Si in the starting powders
on the formation of Ti SiC was studied. The formation mech-
MSR reaction was first discovered by Tschakarov et al. during
the mechanochemical synthesis of metal chalcogenides. Since
then, a large number of investigations on the MSR have been
performed. Different materials have been synthesized by MSR
from the following systems: oxide–metal, metal–chalcogen, ox-
3
2
anism of Ti SiC was analyzed. It is believed that a mechani-
3
2
cally induced self-propagating reaction is ignited during the MA
process. A possible reaction mechanism was proposed to explain
the formation of the final products.
18
ide–oxide, solid–liquid, and solid–gas reaction systems. The
above reactions in the MSR are highly exothermic, which results
in an abrupt increase in the milling vial temperature. So the
ignition temperature measured from the surface of the vial is
usually used to understand the mechanism of the MSR. As to
Ti SiC with a large formation of enthalpy, H (Ti SiC ) is ꢀ547
3
2,
3
2
I. Introduction
1
6
kJ/mol. Theoretically, it should be synthesized by MSR in the
Ti–Si–C system.
3 2
NEW material titanium silicon carbide (Ti SiC ) exhibits
A
promising thermal and mechanical properties. It combines
To date, no authors have reported that the ternary compound
of Ti SiC was fabricated by MA. In this paper, the main pur-
pose is to investigate the feasibility of the formation of Ti SiC
by MA of the elemental powders of Ti, Si, and graphite at room
temperature, and to discuss the effect of Si content on the for-
mation of the desired product.
many of the best properties of both metals and ceramics, for
example, it is an excellent electrical and thermal conductor, very
readily machinable, relatively soft, and it has very good thermal
3
2
3
2
1
,2
shock and high-temperature oxidation resistance.
Ti SiC - or Ti SiC -based composites have been fabricated
by different synthesis methods, such as chemical vapor deposi-
3
2
3
2
3
4
tion (CVD), arc melting, hot isostatic pressing and self-prop-
agation high-temperature synthesis (HIP-SHS), solid-state
reaction, and hot pressing (HP).
been fabricated using the above methods, the sintering temper-
ature always exceeds above 14001C. Can Ti SiC be obtained by
using these methods only at a high temperature? This question
has encouraged many researchers to find new technologies to
3 2
synthesize Ti SiC . One of the most interesting technologies for
obtaining ceramic compounds at room temperature is the me-
chanical alloying (MA) technique. This technique has attracted
considerable interest in recent years. It has been used to synthe-
size various materials such as solid solutions, intermetallics,
amorphous alloys, and ceramic composites.
ic compounds or composites were fabricated by using the MA
technique. For example, MoSi and ZrC were synthesized by
MA of elemental powders of Mo/Si and Zr/C powders, respec-
tively.
by MA of a mixture of Ti and BN. Lee et al. fabricated dense
nanocrystalline TiB –TiC composites by field activation from
high-energy ball-milled reactants. It should be noted that the
MA parameters are very important in the synthesis of the above
compounds or composites. Recently, a few researchers fabricat-
5
6
1,7
II. Experimental Procedure
Although Ti SiC has
3 2
Ti (average particle size: 48 mm, 499.2% purity, General Re-
search Institute for Nonferrous Metals (GRINM), Beijing, Chi-
na), Si (average particle size: 25 mm, 499.9% purity, GRINM,
China), and C (graphite, average particle size: 45 mm, 499.0%
purity, GRINM, China) powders were used in this experiment.
The powders were mixed in dry form in mole ratios
(x 5 1, 1.3, 1.5) according to the following Eq. (1):
3
2
8
–10
3Ti þ xSi þ 2C ! Ti Si C
(1)
Different ceram-
3
x
2
MA was carried out in a planetary ball mill (QM-1SP4) with
stainless-steel milling containers and balls. The rotation speeds
of the milling containers and the platform were set as 500 and
250 rpm, respectively. The milling containers with a volume of
500 mL were emptied by a pump. Three types of balls as milling
medium, 400 balls of 6 mm diameter, 100 balls of 10 mm di-
ameter, and eight balls of 20 mm diameter, were charged into
each container. The weight ratio of ball to powder was 20:1. A
small amount of milled powders was taken out after a selected
milling time for X-ray diffraction (XRD) analysis and scanning
electron microscopy (SEM) observation. The vials were emptied
again, and the MA was performed. XRD analysis was carried
out using a D/Max-rB diffractometer (Rigaku, Tokyo, Japan) at
2
1
1,12
13
2
Shim et al. obtained a TiN/TiB composite powder
1
4
2
ed Ti
3 2
SiC by pressureless sintering of mechanical-alloyed
ultrafine powders consisting of element powders of Ti, Si, and
C.
1
5,16
T. A. Parthasarathy—contributing editor
4
0 kV and 20 mA with CuKa radiation. The morphology of
the powders was observed by a STEREOSCAN 360 SEM
Cambridge, U.K.) equipped with energy-dispersive spectros-
(
Manuscript No. 10976. Received April 15, 2004; approved February 14, 2005.
Supported by ‘863’ program under Grant No: 2003AA332080 and BJTU Talent Foun-
copy (EDS). During the MA, the planetary ball mill was
stopped at different durations in order to measure the surface
temperature of containers using a thermocouple.
dation of China under Grant No: 2004RC005.
Author to whom correspondence should be addressed. e-mail: shibo-li@sohu.com
w
2
092

August 2005
Mechanical Alloying of Elemental Ti, Si, and C Powders
2093
Fig. 2. X-ray diffraction pattern of the mixed powders of 3Ti–Si–2C
after milling for 1.5 h. The card numbers for TiC, Ti SiC , Ti Si , and
TiSi are #32–1383, #40–1132, #29–1362, and #35–0785, respectively.
3
2
5
3
2
Fig. 1. X-ray diffraction patterns of the mixed powders after different
milling times. The card numbers for C, Si, Ti, TiC, and Ti SiC are #75–
3
2
2
TiSi are also present, but TiC is still the main phase with larger
2078, #27–1402, #44–1294, #32–1383, and #40–1132, respectively.
amounts in the milled powders.
Furthermore, a large number of granules with metal bright-
ness in the surface and less than 5 mm in size were found in inner
containers after 1.5 h of milling. The appearance of these gran-
ules is shown in Fig. 3(a). Figure 3(b) shows the fracture surface
of the granules. Many cavities with irregular shape were
wrapped in inner granules. The granules were composed of
III. Results and Discussion
(
1) XRD Analysis and SEM Observation
Figure 1 shows the XRD patterns of Ti, Si, and C mixed pow-
ders subjected to MA at various times. Graphite’s peaks disap-
peared from XRD patterns after only 1 h of milling, because of
the formation of amorphous carbon or distribution in the grain
boundaries of Ti. Both Ti and Si diffraction peaks broadened
and decreased in intensity after 1 h of milling, indicating the
reduction of the average crystallite size, and the buildup of de-
fects and the formation of internal strains. After milling for 4 h,
3 2
Ti SiC , TiC, and small amounts of silicides that were identi-
fied by XRD (see Fig. 7(a)).
The high-magnification micrograph is shown in Fig. 4(a). The
product is highly porous and consists of two types of morph-
ologies including agglomerated TiC particles (marked as arrows
in Fig. 4(a)), and layered Ti SiC particles accompanied by
3
2
smaller TiC. Figure 4(b) shows an enlarged micrograph of the
‘‘I’’ area marked in Fig. 4(a), showing the particles of TiC (iden-
tified by EDS shown in Fig. 5(a)) having a round shape, smooth
surface, and a size less than 2 mm. This feature indicates that TiC
is formed from the reaction between Ti and C through the dis-
solving and precipitating mechanism in the liquid. The origin of
liquid in this system will be discussed in section III(2). Figure
4(c) shows the enlarged micrograph of the ‘‘II’’ area, showing
3 2
the TiC phase and the desired phase Ti SiC with a weak re-
flection peak were present. The reflection peak belonging to
Ti SiC disappeared completely after milling for 8 h. This sug-
3
2
3 2
gests that the Ti SiC phase had been transformed to a nano-
crystallite or amorphous phase. With increasing milling time, all
of the TiC peaks broadened and decreased in intensity. No new
phase was found, even though the milling time had been up to
60 h. The disappearance of the diffraction peak of Ti
increasing milling time suggests that the Ti SiC phase may be
3
SiC
2
with
3 2
larger Ti SiC particles surrounded by smaller TiC particles.
3
2
Some of the smaller TiC particles were embedded in the coarse
Ti SiC grains. Many dents left on the surfaces of Ti SiC grains
formed in the range of 1–4 h. So the milled powders after milling
from 1 to 3 h can be identified by XRD. The results show that
Ti SiC is formed after only 1.5 h of milling. The XRD pattern
3
2
3
2
were a result of debinding of the TiC. Plate-like grains with lay-
ered characteristics are typical microstructures for Ti SiC . Rod-
like Ti SiC grains (identified by EDS shown in Fig. 5(b)) were
also found in the fracture surfaces (Fig. 4(d)). These features
3
2
3
2
of the different powders subjected to 1.5 h milling is shown in
Fig. 2, from which it can be found that the peaks of Ti Si and
3
2
5
3
Fig. 3. Granules formed by mechanical alloying after milling for 1.5 h shown in (a) and (b) the fracture surface of the granule.

2
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Journal of the American Ceramic Society—Li and Zhai
Vol. 88, No. 8
Fig. 4. Scanning electron micrographs of the formed granules by mechanical alloying of the 3Ti–Si–2C powders after milling for 1.5 h. (a) Micro-
structure of the fracture surface, (b) and (c) higher magnification micrographs taken from ‘‘I’’ and ‘‘II’’ areas, respectively, marked in (a), (d) morphology
of the rod-like Ti SiC grains.
3 2
indicate that Ti SiC
3
2
had developed into two types of micro-
structures, with the plate-like and the rod-like forms. The above
results confirm that the ternary-phase Ti SiC can be fabricated
Ti
3 2
SiC to form. So addition of excess Si in the composition
1
9,20
can compensate for Si loss during heat treatment. In the
previous work, we found that excess of Si introduced in the
3
2
by MA of Ti, Si, and C powders at room temperature.
It has been proved that the elemental Si tends to evaporate at
elevated temperatures during sintering of Ti, Si, and C powders
to fabricate Ti SiC . This leads to a deviation from the target
3
2
composition, which makes it difficult for the single-phase
Fig. 5. Energy-dispersive spectroscopy spectra from (a) smaller, round-
shaped particles in Fig. 4(b), and (b) rod-like grains in Fig. 4(d) (the
unmentioned peaks belong to Au).
Fig. 6. Scanning electron micrograph of the milled powders containing
smaller granules after milling of 3Ti–1.3Si–2C for 1.5 h.

August 2005
Mechanical Alloying of Elemental Ti, Si, and C Powders
2095
Ti–Si–C mixed powders can facilitate the formation of Ti SiC
3
using an HP technique. So Si with excess of 30 and 50 mol%
are, respectively, added to the starting material (marked as
Ti SiC by MA. Many granules, similar to those formed in the
3
2
2
2
0
3Ti–Si–2C as shown in Fig. 3(a), are also found in the containers
because of MA of either 3Ti–1.3Si–2C or 3Ti–1.5Si–2C after
milling for 1.5 h. Figure 6 shows the micrograph of the milled
powders after sifting out the larger granules; it can be observed
that there are still large amounts of smaller granules with size
less than 50 mm.
3Ti–1.3Si–2C and 3Ti–1.5Si–2C, respectively) for synthesis of
The larger granules with size o5 mm formed with different
contents of Si were pulverized, and then identified by XRD. The
results of XRD patterns are shown in Fig. 7. It can be observed
3 2
that the contents of both Ti SiC and silicides increase with in-
creasing Si content.
Figure 8(a) shows the fracture surface of the larger granules
formed from 3Ti–1.3Si–2C. In the rich-Ti SiC areas, smaller,
round-shaped TiC particles distribute randomly. Some Ti SiC
grains with a smooth surface develop a layered morphology
Fig. 8(b)).
2
It should be noted that some Ti SiC grains are also found in
3
2
3
2
(
3
the TiC agglomerations as shown in Fig. 9(a), which is different
from the observation in Fig. 4(b). No Ti SiC grains can be
3
2
found in the TiC agglomerations, as shown in Fig. 4(b). This
indicates that the presence of more Si does favor the formation
of Ti SiC . Figure 9(b) shows a higher magnification micro-
Fig. 7. X-ray diffraction patterns of the powders from the pulverized
granules (a) 3Ti–Si–2C, (b) 3Ti–1.3Si–2C, and (c) 3Ti–1.5Si–2C.
3
2
graph of the marked square taken from Fig. 9(a). It can be
Fig. 8. Scanning electron micrographs of the fracture surface of the granules formed after milling of 3Ti–1.3Si–2C for 1.5 h. (a) Microstructure of the
Ti SiC -rich area and (b) high magnification taken from (a).
3
2
Fig. 9. Scanning electron micrographs of the fracture surface of the granules formed after milling of 3Ti–1.3Si–2C for 1.5 h. (a) Ti
tributed in TiC-agglomerated areas, (b) higher magnification of the marked square in (a).
3 2
SiC grains dis-

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Vol. 88, No. 8
Fig. 10. Energy-dispersive spectroscopy spectrum from the gray phase
marked in Fig. 9(a) (the unmentioned peak belongs to Au).
clearly observed that some TiC particles are enwrapped or
linked by gray phases. The gray phases were identified by
EDS (see Fig. 10) to be composed of about 84 at.% Ti and 16
at.% Si, indicating that the Ti–Si eutectic liquid had formed in
the high-temperature system because of the occurrence of an
exothermic reaction. The formation of this feature is explained
in the following section.
Figure 11 shows the fracture surface of the granules formed
from 3Ti–1.5Si–2C. The observation from Fig. 11(a) is different
from the two former observations (as compared with Figs. 4 and
8
). The fracture surface of the granules shown in Fig. 11(a) ap-
pears denser than that formed both in 3Ti–Si–2C and 3Ti–1.3Si–
C, which could be attributed to the formation of more Ti–Si
2
phases that filled pores. From the above observations, it can be
seen that the microstructure or morphology of grains in the
formed granules changes as Si increases in the mixed powders.
It should be noted from Fig. 11(b) that all of the Ti SiC
3
2
grains exhibit smooth surfaces, distributing in the TiC-agglom-
erated areas. Figure 11(c) shows the morphology of the frac-
ture surfaces after being treated with HF acid solution
(HF:H O 5 1:1). It can be found that Ti SiC grains become
2 3 2
sharp at the edges. This feature is mainly attributable to the fact
that the surfaces of Ti SiC grains are covered with a thin layer
of the Ti–Si phase as Ti SiC precipitated from the Ti–Si liquid,
3
2
3
2
forming a smooth morphology. The HF solution easily dissolves
silicides; therefore, Ti–Si compounds such as TiSi and Ti Si
are leached, leaving Ti SiC and TiC only.
2
5
3
3
2
(
2) Reaction Mechanism for Formation of Ti SiC2
3
As mentioned above, the MSR is easily triggered, while MA of
the alloy system takes place with large exothermic heat. During
the MA, the MSR may be ignited after a certain activation time,
as milling reduces the particle size, thoroughly mixes the com-
ponents, and increases the number of chemically active defect
Fig. 11. Scanning electron micrographs of the fracture surface of the
granules formed after milling of 3Ti–1.5Si–2C for 1.5 h. (a) microstruc-
ture of the fracture surface, (b) higher magnification micrograph of the
TiC agglomeration area, taken from the center part of Fig. 11(a), with
1
8
sites.
In the present work, it is certain that the formation of Ti
3 2 3 2
smooth Ti SiC grains distributing, (c) morphology of Ti SiC grains
3
SiC
2
after treatment with HF solution.
is caused by the MSR. During milling of Ti, Si, and C powders,
the MSR is not ignited at the beginning of the milling process. It
first undergoes a period of initial milling (incubation). During
the incubation, the mixed powders are subjected to a repeated
fracture and welding process. Proper pulverization results in the
refinement of particles. As the milled powders are of a critical
size, the diffusion distance decreases and a large surface forms,
which contributes the occurrence of the ignition reaction. In the
Ti–Si–C system, it is believed that a reaction between Ti and C
occurs first because of the high chemical affinity of Ti to C. It is
not possible for SiC to form first, because the formation heat of
TiC, DH 5 185 kJ/mol, is much larger than that of SiC, DH 5 73
16
kJ/mol, indicating that the MSR is easier to initiate in the Ti–
C system than in the Si–C system with the same energy input.
Furthermore, self-sustenance of a combustion reaction requires
that the adiabatic temperature (Tad) be at least 1800 K. For TiC,
the adiabatic temperature Tad is 3290 K, but that of SiC is 1860
K, which also indicates that the reaction between Ti and C for

August 2005
Mechanical Alloying of Elemental Ti, Si, and C Powders
2097
formation of TiC occurs easily during the MSR. The reaction
between Ti and C releases a large amount of heat, which leads to
the formation of a Ti–Si eutectic liquid, because the Ti–Si system
exhibits two eutectic reactions for the Si–TiSi
compositions, both at a temperature of 13331C.
2
21and Ti–Ti
5 3
Si
The occurrence of MSR can be confirmed by the temperature
rise on the surface of the containers. The temperature increase at
the surface of two containers, one containing only milling balls,
and the other containing the same balls and the Ti–Si–C pow-
ders, with a weight ratio of ball to powder of 20:1, is investi-
gated. Figure 12 shows the temperature rise as a function of
different milling durations. As only the milling balls are intro-
duced into the container, the temperature rises continuously and
then becomes slow after milling for 90 min. The temperature
was measured to be 581C after milling for 100 min, which is
mainly because of the colliding balls and friction between the
balls and the container wall. However, the temperature increase
with the powders charge is higher than that of the former, as
shown in Fig. 12. This indicates that the friction between the
balls and powders, besides the colliding balls, produces more
energy in the container before milling for 80 min. It should be
noted from Fig. 12 that the surface temperature increases
abruptly to 881C after milling for 90 min, which mainly occurs
because of an exothermal reaction. It is very difficult to measure
the temperature of the powders directly during MA, but it can
Fig. 12. Temperature increase versus different milling times. (-m-) only
balls charged in the container, (-& -) both balls and powders charged in
the container.
2
2
be calculated according to Tad in the SHS reaction. Ye et al.
Fig. 13. Proposed mechanism of mechanically induced self-propagating reaction during mechanical alloying of the Ti–Si–C system. (a) Initial milling
duration. The milled powders decrease in size and distribute to become more homogeneous, (b) C atoms diffuse along the Ti grain boundaries and
remain there, forming Ti–C layers, (c) Ti–C layers are ignited with considerable heat release that leads to Ti–Si melt formation. TiC nuclei precipitate
3 2
from the liquid Ti–Si, (d) Ti SiC is formed by the reaction between TiC and Ti–Si then develops a layered morphology.

2
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Journal of the American Ceramic Society—Li and Zhai
Vol. 88, No. 8
reported that the Ti–C reaction led to an increase in temperature
up to 1700 K in certain regions during MA; the Al–Ti–C system
in the stainless-steel container led to an increase in the surface
temperature up to 701C after being milled for 210 min. The re-
action temperature in this research is estimated to be above 1700
K because of the increase in surface temperature up to 881C. So
it is possible for the Ti–Si melt to form in a higher temperature
system.
(NH ) SO 1H SO solution. Using the above-mentioned syn-
4
thesis technique, pure Ti SiC powders can be obtained, with the
3 2
advantage that not only is the fabrication time shortened but
also high sintering temperature is avoided and a large amount of
energy is saved as compared with the reported technologies
mentioned in the Introduction.
4
2
4
2
IV. Conclusions
Finally, in a high-temperature system, formation of the Ti–Si
liquid spreads over the TiC particles, resulting in the rearrange-
ment of particles. Ti SiC is formed at the interfaces between the
Ti SiC has been synthesized by MA of Ti, Si, and C powders at
3 2
room temperature after milling for only 1.5 h. With increasing
Si content in the starting composition, not only did the amount
3
2
Ti–Si liquid and TiC particles as follows
of Ti SiC
3
2
rise but also its morphology changed, to become
SiC grains are
2
TiC þ Ti2Si ðliquidÞ ! Ti3SiC2
(2)
smooth. In the latter case, it is believed that Ti
3
2
covered with a thin layer of the Ti–Si phase as it precipitates
from the Ti–Si liquid.
The main reason for the formation of Ti SiC is that the
MSR is ignited during MA of elemental powders. During the
MSR process, a reaction between Ti and C is first ignited with a
large amount of heat release, which induces Ti and Si to form a
eutectic liquid, and then TiC dissolves into the melt and reacts
with it to form Ti SiC . Finally, Ti SiC precipitates and devel-
3 2 3 2
op a layered morphology. A simple reaction mechanism is pro-
posed to explain the formation of the final product.
A possible reaction mechanism is proposed as shown in
Fig. 13. At the initial MA stage, the mixed powders, consisting
of two brittle components of Si and C, become fragmented and
their particle sizes reduce continuously. Some fine Si and C par-
ticles are embedded into Ti particles, resulting in the refinement
of the Ti particles. With increasing milling time, particle distri-
bution tends to become more homogeneous (Fig. 13(a)). Once
the particle size decreases to a critical size, large areas of grain
boundaries are formed, and severe internal strain and defects are
induced by MA. It is well known that grain boundaries can act
as sources for dislocations. The defects and dislocations provide
a rapid diffusion pathway. It is assumed that a large amount of
C atoms diffuse rapidly through the pathway and accumulate in
the grain boundaries of Ti, forming Ti–C layers (Fig. 13(b)). In
such layers, Ti–C is only a transitional bonded state that is not
the chemical TiC, but the activation energy of Ti–C for the re-
3
2
References
1
M. W. Barsoum and T. El-Raghy, ‘‘Synthesis and Characterization of a
Remarkable Ceramic: Ti
3
SiC
L. Farber, M. W. Barsoum, A. Zavaliangos, and T. El-Raghy, ‘‘Dislocations
and Stacking Faults in Ti SiC ,’’ J. Am. Ceram. Soc., 81 [6] 1667–81 (1998).
C. Racault, F. Langlais, and C. Bernard, ‘‘On the Chemical Vapour Deposition
of Ti SiC from TiCl –SiCl –CH –H Gas Mixtures Part I: A Thermodynamic
2
,’’ J. Am. Ceram. Soc., 79 [7] 1953–6 (1996).
2
3
2
3
2
3
action of TiC is lower than that of unmilled Ti and C powders.
3
2
4
4
4
2
Approach,’’ J. Mater. Sci., 29, 5023–40 (1994).
S. Arunajatesan and A. H. Carim, ‘‘Synthesis of Titanium Silicon Carbide,’’
J. Am. Ceram. Soc., 78 [3] 667–72 (1995).
In other words, the formation of TiC through Ti–C layers is
easily induced by the impact energy of ball milling. Once the Ti–
C layers are ignited, the high heat released propagates rapidly
and leads to an increase in temperature in certain regions. The
local temperature is high enough to induce melt Ti–Si forma-
tion; the previously formed TiC dissolves into the Ti–Si melt and
nucleates from it. At the same time, several pores are also
wrapped into the melt (Fig. 13(c)). In the high-temperature re-
gion, some TiC particles react with the Ti–Si liquid to form
4
5
3 2
J. Lis, Y. Miyamoto, R. Pampuch, and K. Tanihata, ‘‘Ti SiC -Based Materials
Prepared by HIP-SHS Techniques,’’ Mater. Lett., 22, 163–8 (1995).
C. Racault, F. Langlais, and R. Naslain, ‘‘Solid-State Synthesis and Charac-
6
terization of the Ternary Phase Ti
3
SiC
S. B. Li, L. T. Zhang, and L. F. Cheng, ‘‘Microstructure and Thermal Expan-
sion of Ti SiC ,’’ Mater. Sci. Tech., 18, 1494–6 (2002).
2
,’’ J. Mater. Sci., 29, 3384–92 (1994).
7
3
2
8
P. G. McCormick, ‘‘Application of Mechanical Alloying to Chemical Refin-
ing,’’ Mater. Trans. JIM, 36, 161–9 (1995).
9
C. Suryanarayana, ‘‘Mechanical Alloying and Milling,’’ Prog. Mater. Sci., 46,
–184 (2001).
10
3 2 3 2
Ti SiC . Finally, Ti SiC grains start precipitating from the melt
1
and develop into a layered morphology. A final microstructure
with high porosity is formed, as shown in Fig. 13(d). The reason
why the TiC agglomerations are always found at the surface of
the pores is that the capillary spreading and particle rearrange-
ment under the liquid existing are confined near the closed
pores, where the content of the Ti–Si liquid is less and some
TiC fine particles grow, forming agglomerations. If the Ti–Si
melt existed in the agglomerations, a reaction between TiC and
E. Gaffet, M. Abdellaoui, and N. M. Gaffet, ‘‘Formation of Nanostructual
Materials Induced by Mechanical Processings,’’ Mater. Trans. JIM, 36, 198–209
1995).
(
11
S. N. Patankar, S. Q. Xiao, J. J. Lewandowski, and A. H. Heuer, ‘‘The
Mechanism of Mechanical Alloying of MoSi ,’’ J. Mater. Res., 8, 1311–6 (1993).
B. K. Yen, ‘‘X-Ray Diffraction Study of Mechanochemical Synthesis and
2
12
Formation Mechanisms of Zirconium Carbide and Zirconium Silicides,’’ J. Alloy
Compounds, 268, 266–9 (1998).
13
J. H. Shim, J. S. Byun, and Y. W. Cho, ‘‘Mechanochemical Synthesis of
Nanocrystalline TiN/TiB Composite Powder,’’ Scripta Mater., 47, 493–7 (2002).
J. W. Lee, Z. A. Munir, and M. Ohyanagi, ‘‘Dense Nanocrystalline TiB –TiC
2
14
3 2
Ti–Si would occur, leading to the formation of Ti SiC . This is
2
why Ti SiC can be found in the agglomerations with an in-
3
2
Composites Formed by Field Activation from High-Energy Ball Milled Reac-
tants,’’ Mater. Sci. Eng., 325 A, 221–7 (2002).
crease in Si content in the starting powders, as shown in Figs. 9
and 11. Furthermore, some of the unreacted Ti–Si phases may
be left behind (as shown in Fig. 9) while the local temperature
decreases rapidly, because the MSR is very short and the heat is
absorbed rapidly by the balls and containers.
15
J. F. Li, T. Matsuki, and R. Watanabe, ‘‘Mechanical-Alloying-Assisted Syn-
thesis of Ti SiC Powder,’’ J. Am. Ceram. Soc., 83 [4] 1004–6 (2000).
H. R. Orthner, R. Tomasi, and W. J. Botta F, ‘‘Reaction Sintering of Tita-
3
2
16
nium Carbide and Titanium Silicides Prepared by High-Energy Milling,’’ Mater.
Sci. Eng., 336A, 202–8 (2002).
17
.
G. Chr. Tschakarov, G. G. Gospodinov, and Z. Bontshev, ‘‘Uber den Mech-
Once a highly exothermic reaction takes place in a small local
volume, the reaction heat will be quickly absorbed by the milling
vial and balls; heat loss inhibits the formation of a self-sustain-
ing reaction front, which cannot propagate through the entire
powder mixture, and instead occurs locally at the ignition spot.
So each ignited point ultimately forms a granule. This is why a
large amount of granules are found in the container after the
MA process is over.
anismus der mechanochemischen Synthese Anorganischer Verbindungen,’’ J. Sol-
id. State. Chem., 41, 244–52 (1982).
18
L. Takacs, ‘‘Self-Sustaining Reactions Induced by Ball Milling,’’ Prog. Mater.
Sci., 47, 355–414 (2002).
19
C. S. Park, F. Zheng, S. Salamone, and R. K. Bordia, ‘‘Processing of Com-
posites in the Ti–Si–C System,’’ J. Mater. Sci., 36, 3313–22 (2001).
20
S. B. Li, J. X. Xie, L. T. Zhang, and L. F. Cheng, ‘‘Synthesis and Some
Properties of Ti SiC by Hot Pressing of Ti, Si and C Powders: Part I: Effect of
Starting Composition on Formation of Ti SiC ,’’ Mater. Sci. Tech., 19, 1442–6
2003).
3
2
3
2
(
21
In conclusion, Ti
emental powders of Ti, Si, and C at room temperature. If re-
quired, pure Ti SiC can be obtained by using the procedures
3
SiC
2
can be synthesized by MA of the el-
Z. F. Zhang, Z. M. Sun, H. Hashimoto, and T. Abe, ‘‘Effects of Sintering
Temperature and Si Content on the Purity of Ti SiC Synthesized from Ti/Si/TiC
3
2
Powders,’’ J. Alloys Compounds, 352, 283–9 (2003).
L. L. Ye, Z. G. Liu, S. D. Li, M. X. Quan, and Z. Q. Hu, ‘‘Thermochemistry
3
2
22
6
reported for leaching of the pulverized granules, for example,
by first using the HF solution for removing the Ti–Si com-
pounds, and then removing TiC by heating the powders in
air to 5001C and washing the oxidized powders with hot
of Combustion Reaction in Al–Ti–C System During Mechanical Alloying,’’
J. Mater. Res., 112, 616–8 (1997).
23
N. Q. Wu, S. Lin, J. M. Wu, and Z. Z. Li, ‘‘Mechanosynthesis Mechanism of
TiC Powders,’’ Mater. Sci. Tech., 14, 287–91 (1998).
&