a new approach to fabricating tib2-tic composite using
TRANSCRIPT
International Journal of Engineering & Technology Sciences (IJETS) 2 (2): 193-203, 2014 ISSN 2289-4152 © Academic Research Online Publisher
Research paper
A new approach to fabricating TiB2-TiC composite using self-propagation
high temperature synthesis via pressureless sintering
Mitra Akhtari Zavareh
a,*, Ahmed Aly Diaa Mohammed Sarhan
b, Malihah Amiri Roudan
c,
Parisa Akhtari Zavareh d
a,b,c,d
Department of Mechanical Engineering, Faculty of Engineering, University Malaya, Kuala Lumpur,
Malaysia
* Corresponding author. Tel.: 0060176443409;
E-mail address:[email protected]
A b s t r a c t
Keywords:
Self- propagation,
Synthesis,
Titanium diboride,
Titanium carbide,
Ceramics composite,
Microstructure.
Titanium diboride/titanium carbide (TiB2- TiC) composites are favorable materials
with appeal in different industrial components, such as wear parts and high-
temperature parts. Conventional sintering techniques have many limitations with
respect to material density. Thus, a simultaneous synthesis technique was used in
this study with different amounts of carbon content and constant processing time
and temperature. The chemical reaction between titanium metal, boron and carbon
particles completed at 1200oC after 1 hour. Pure TiB2- TiC ceramic composite was
ultimately produced. The hardness values of the TiB2- TiC compacts obtained
decreased with increasing carbon per titanium molar ratio.
Accepted:12 April2014 © Academic Research Online Publisher. All rights reserved.
1. Introduction
Titanium diboride/titanium carbide (TiB2- TiC) composites are a favorable material with appeal in
different industries such as aircraft wear and high temperature components. Significant activity exists
in the development and fabrication of TiB2- TiC composites. This composite has many characteristics,
among which high melting point and hardness, good thermal shock resistance and high temperature
stability, electrical conductivity, and elastic modulus. It is also an exceptional option in applications
with high performance cutting tools and abrasives [1-5].
Furthermore, this material has low density, which makes it applicable for aircraft propulsion systems
and space vehicle thermal protection [6, 7]. However, the high, strong covalent bonding and low self-
diffusion coefficients of the component cause difficult densification of this composition by traditional
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methods like hot pressing or hot-isostatic pressing (HIPing) since high temperatures around 3300⁰C
are required. These properties make TiB2 and TiC the subject of numerous, extensive studies [8-10].
Reaction sintering and hot pressing, with or without sintering aids, are common fabrication methods
for producing dense, solid bodies of these ceramics [11]. However, both methods require liquid-
forming additives or high sintering temperatures. During liquid phase sintering, a low melting phase is
created at the grain boundaries. For instance, a small percentage of nickel in the chemical composition
of titanium, boron and carbide causes a direct reaction with raw materials, and a dense TiB2- TiC
composite is fabricated [12]. Meanwhile, at higher temperatures grain growth becomes predominant
[13]. Another process that can be synthesized is self-propagation high-temperature synthesis (SHS)
[14]. These processing methods have many advantages; however, a high degree of covalent bonding
and low self-diffusion create some limitations in achieving fully-dense composites [15].
Nonetheless, such limitations can be overcome by applying an external force during synthesis. The
external load causes TiB2-TiC powder to consolidate into dense solid bodies [16, 17]. The process is
high-pressure self-combustion synthesis (HPCS) and a maximum density of ∼96.5% is obtained. Self-
propagation synthesis and dynamic compaction of elemental powders can also be used to fabricate
dense TiB2 [18, 19].
Producing and fabricating TiB2-TiC in one step via SHS is an economically effective method that can
be applied in industry. The SHS process consumes extreme internal thermal energy generated from
the chemical reaction, making SHS an energy efficient means of producing advanced, high
temperature materials such as TiB2-TiC. Besides, the high temperature reaction of initial element
powders including Ti, B, and C provides far-from-equilibrium conditions that may facilitate self-
organized processes, self-purification and homogenization processes. Very unique structures can be
achieved at far from equilibrium SHS conditions another advantage of the process [20-23].
Additionally, the SHS process is an exothermic reaction. During the formation of some refractory
material, extreme heat is generated between either two or more solid reactants and gas. This reaction
is propagated spontaneously and helps the reaction to convert raw materials into pure refractory
product. The self-sustaining merit from the exothermic reaction and low time and energy
requirements is an advantage of this process material [20-23]. Conventional methods have some
limitations regarding method complexities and high cost. The SHS process has overcome such
limitations with its simplicity of facilities and reaction heat [24, 25]. Therefore, SHS is a good choice
for fabricating different refractory materials. This research work applies a novel experimental design
to produce and fabricate a pure composite in one step, with the characterization and development of
TiB2-TiC composite through self-propagating high-temperature synthesis via pressureless sintering at
a low temperature of about 1200°C.
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2. Experimental procedures
The fundamental aspect behind Ti-B-C design is to investigate the porosity reduction at different
amounts of carbon content. The initial powders were Ti (150 μm; Sigma-Aldrich, St Louis, MO,
USA), B (amorphous; Sigma-Aldrich) and C (50 μm; Merck) and these were dried and blended before
mixing. The Ti+2B+xC mixture, according to the predetermined compositions for each specimen (x=
1, 1.1, 1.2 and 1.3), was prepared in a planetary ball mill, separately, at 300 rpm for 5 h. Then, each
mixture in a cylindrical die of 12.7 mm diameter was subsequently pressed in a uniaxial hydraulic
press under 3 tons, producing a cylindrical specimen approximately 5-8 mm high.
The specimens were sintered in a tube furnace filled with Argon gas. The sintering cycle profile from
30 to 1200ºC is shown in Figure 1. A holding time of 1 hour for a sintering temperature of 1200°C
was applied in order to ensure that expansion throughout the specimen occurred coherently during
heating.
Fig. 1: Thermal cycle used to produce TiB2-TiC
3. Results and discussion
3.1. Combustion characteristics
Figure 2 shows an optical image of combusted [(1Ti+2B) + (1Ti+xC)] mixture when x=1.1 and 1.2,
while Figure 3 illustrates an optical image of combusted [(1Ti+2B) + (1Ti+xC)] mixture when x= 1
and 1.3. The results of this study indicate that the amount of carbon content has direct influence on the
combustion behavior of the compacted matrix. Pores and crevices may be generated by unbalanced
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diffusion between the reagent particles or by vaporization and expulsion of volatile impurities due to
high temperatures.
Fig. 2: Optical image of combusted [(1Ti+2B) + (1Ti+xC)] mixture when x=1.1 and 1.2
Fig. 3: Optical image of combusted [(1Ti+2B) + (1Ti+xC)] mixture when x=1 and 1.3
As shown in Figure 2, when the carbon content x=1.1 and 1.2 the results indicate the effect of powder
composition on synthesis and consolidation. The two end sides are swollen, while the interface
between the two pieces is concaved, meaning that a violent combustion reaction occurred. The major
cracks observed in the samples mean that considerable out-gassing occurred. In addition, the color of
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the samples completely changed from black to light gray. But when the amount of carbon was x=1
and 1.3, as seen in Figure 3, the color did not change significantly. Furthermore, the specimens’
dimensions did not change considerably, so no shrinkage or expansion took place.
3.2 The morphology and phase analysis of the surface
To investigate the surface phase analysis, XRD analyses corresponding to the as-synthesized
composites with different amounts of carbon in the initial mixture are shown in Figures 4(a), (b), (c)
and (d).
(a) x=1
(b) x=1.1
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(c) x=1.2
(d) x=1.3
Fig. 4: XRD analysis of synthesized [TiB2-TiC] mixture with different carbon content (a) x=1, (b) x=1.1, (c)
x=1.2 and (d) x=1.3
Figure 4(a) signifies that where carbon content x=1, TiB2, TiC and TiO0.325 are observed in the
product. It means some amount of C was oxidized and left the system, therefore the insufficient C
caused the reaction of Ti with the oxygen available in the chamber. The source of oxygen is either
from air trapped inside the sample during compaction or the oxygen content mixed with argon gas. In
Figures 4(b) and (c), where x=1.1 and x=1.2, the products are composed of TiC or TiB2 with no
intermediate phases, suggesting complete phase conversion of the reactants with no remaining pure
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materials and oxidation. Apparently, an increase in carbon provides Ti with sufficient carbon for
reaction, and it prevents oxidation from occurring in the sample (Figure 4(d), where x=1.3 indicates
TiB2, TiC and C in the product). This means the percentage of carbon in the mixture was high;
therefore, the amount of carbon in this sample was more than sufficient. Although some C was
oxidized and left the system, this amount of carbon is not acceptable.
To investigate the surface morphology, SEM micrographs of samples with various amounts of carbon
are shown in Figure 5.
(a) x=1
(b) x=1.1
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(c) x=1.2
(d) x=1.3
Fig. 5: SEM patterns of synthesized [(1Ti+2B) + (1Ti+xC)] mixture with (a) x=1, (b) x=1.1, (c) x=1.2 and (d)
x=1.3
In Figure 5 (a) where x=1 the SEM micrograph indicates less pores in the microstructure compared
with other samples where x is bigger than 1 (x>1). In addition some smaller and bright, white faces
are also observed, which indicate titanium oxide. Clearly, the oxide phase appeared on selected
regions, where a Carbon deficit occurred near Ti. When the carbon content increased up to x=1.1
(Figure 5(b)) a solidified liquid formation in cloudy shapes with the role of matrix for the small grains
is observed. The small grains developed in the matrix and are distributed uniformly throughout. The
microstructure demonstrates a porous product with shapeless grains joining to each other in some
parts, while small grains are discrete crystals distributed to them. Further increasing the carbon
content to x=1.2, as shown in Figure 5(c), sponge-shaped sample features are observed. The cavities
are likely to be the result of entrapped gases related to the rapid growth of TiB2 grains as well as
volume changes during phase transformation. Grain size in this specimen is approximately big. It
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means that the specimen temperature during combustion synthesis increased, causing all the grains to
melt and compete to grow and integrate. Sample cracking and failure may have occurred during the
reaction of titanium and boron, because this chemical reaction liberates a great amount of heat [25].
Eventually, at carbon content of x=1.3 (Figure 5(d)) the sample features include a black matrix with
bright grains growing on it. Light cracks are observed between large grains in the matrix and
microcracks are evident in the grains. Pores of various sizes are distributed in the grains.
3.3 Hardness analysis
Vickers hardness is presented in Figure 6. Grain and porosity size has obvious influence on the
results.
Fig. 6: Microhardness of the combusted mixtures
When the amount of carbon is x=1.1 and 1.2, hardness sharply increases. According to the XRD of
these groups, the amount of TiB2-TiC is greater than the other groups and besides, they have less
amorphous content. On the other hand, when the carbon content is x=1.3 the difference in
microhardness is not as much as when x=1. The XRD of these groups signifies that the amount of
TiB2-TiC decreases compared with x=1.1 and 1.2. This is related to the role of pore size, shape, and
distribution throughout the sample. Although the samples changed microscopically, their
microhardness remained in the same range without significant change. It is suggested that even if any
changes occurred in the microstructure, their influence was not significant on microhardness.
However, microscopically significant changes were observed. This can strongly be related to the pore
distribution dominating the microhardness measurement results.
It is clear that increasing the amount of carbon has a direct effect on product hardness owing to the
fact that carbon has higher porosity. Carbon also has low hardness and is softer compared with other
composite materials. This explains why increasing the amount of carbon to x=1.3 in the composite
reduces composite material hardness.
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4. Conclusion
The system’s chemical reaction depends on solid state diffusion between B, C and Ti. Moreover, the
diffusion of carbon in the titanium matrix during sintering is faster than boron, which is why the
emergence of TiC occurs earlier than TiB2. A pure TiB2-TiC composite was produced and fabricated
from Ti, B and C powders using SHS in one step by optimizing the carbon content. Furthermore,
oxidation was prevented by varying the C:Ti ratio. The best yield was achieved when C:Ti=1:1 and
1:2. Maximum hardness was achieved when the amount of carbon was 1.2 and hardness was HV=
563.
References
[1] LB Nikzada, R Licheria, MR Vaezib, R Orrùa, G Caoa. Chemically and mechanically activated
combustion synthesis of B4C–TiB2 composites. International Journal of Refractory Metals and Hard
Materials 2012; 35 (4): 41–48.
[2] HSP Fard, HR Baharvandi, H Abdizadeh, B Shahbahrami. Chemical synthesis of nano-titanium
diboride powders by borothermic reduction. International Journal of Modern Physics 2008; 22 (18-
19): 3179–84.
[3] A Biedunkiewicz, P Figiel, U Gabriel, M Sabara, S Lenart. Synthesis and characteristics of
nanocrystalline materials in Ti, B, C and N containing system. Central European Journal of Physics
2012; 2 (1): 417–22.
[4] D Vallauri, IC At´ıas Adrian´a, A Chrysanthou. TiC–TiB2 composites: A review of phase
relationships, processing and properties. Journal of the European Ceramic Society 2008; 8 (2): 1697–
1713.
[5] G Wen, SB Li, BS Zhang, ZX Guo. Reaction synthesis of TiB2 –TiC composites with enhanced
toughness. Acta Metallurgica et Materialia 2001; 21 (8): 1463-1470.
[6] R Licheri, R Orrù, G Cao. Chemically activated combustion synthesis of TiC–Ti composites.
Materials Science and Engineering A 2004; 21 (1-2): 185–97.
[7] RR Taylor, SA Pirzada. Ceramic carbide powder synthesis in a non-transferred arc plasma flow
reactor. Materials and Manufacturing Processes 2007; 8 (2): 501-507.
[8] M Razavi, R Ghaderi, MR Rahimipour, M Ostad Shabni. Synthesis of TiC Master Alloy in
Nanometer Scale by Mechanical Milling. Materials and Manufacturing Processes 2012; 12 (3): 1310-
1314.
[9] H Zhao, YB Cheng. Formation of TiB2-TiC composites by reactive sintering. Ceramics
International 1999; 12 (4): 353-358.
[10] BH Lohse, A Calka, D Wexler. Synthesis of TiC by controlled ball milling of titanium and
carbon. Journal of Materials Science 2007; 10 (6): 669–75.
Mitra Akhtari Zavareh et al. / International Journal of Engineering & Technology Sciences (IJETS) 2 (2): 193-203, 2014
203 | P a g e
[11] MW Barsoum, B Houng. Transient plastic phase processing of titanium-boron-carbon
composites. Journal of the American Ceramic Society 1993; 27 (6): 1445-1451.
[12] B Ghosh, SK Pradhan. Microstructure characterization of nanocrystalline TiC synthesized by
mechanical alloying. Materials Chemistry and Physics 2010; 10 (2-3): 537–45.
[13] J Intrater. Advanced Synthesis and Processing of Composites and Advanced Ceramics Ceramic
Transactions. Materials and Manufacturing Processes 1997; 16 (1): 1185-1186.
[14] D Horvitz, I Gotman. Pressure-assisted SHS synthesis of MgAl2O4–TiAl in situ composites with
interpenetrating networks. Acta Materialia 2012; 50 (2): 1961–1971.
[15] LU Jianbang, S Shili, Q Feng, W Yawei, J Qichuan. Compression properties and abrasive wear
behavior of high volume fraction TiCx–TiB2/Cu composites fabricated by combustion synthesis and
hot press consolidation. Materials & Design 2012; 40 (6): 157-162.
[16] BS Du, P Sameer, R Narendra, B Dahotrea. Phase constituents and microstructure of laser
synthesized TiB2–TiC reinforced composite coating on steel. Scripta Materialia 2008; 59 (10): 1147–
50.
[17] L Wang, MR Wixom. Structural and mechanical properties of TiB2 and TiC prepared by self-
propagating high-temperature synthesis/dynamic compaction. Journal of Materials Science 1994; 29
(3): 534-543.
[18] AR Keller, M Zhou. Effect of microstructure on dynamic failure resistance of titanium
diboride/alumina ceramics. Journal of the American Ceramic Society 2003; 12 (3): 449-457.
[19] F Akhtar. Microstructure evolution and wear properties of in situ synthesized TiB2 and TiC
reinforced steel matrix composites. Journal of Alloys and Compounds 2008; 10 (1-2): 491–7.
[20] G Wen, SB Li, BS Zhang, ZX Guo. Reaction synthesis of TiB2–TiC composites with enhanced
toughness. Acta Metallurgica et Materialia 2011; 15 (8): 1463–1470.
[21] Z Lei, S Ping, J Qichuan. The mechanism of combustion synthesis of (TiCx Ny-TiB2)/Ni from a
Ni-Ti-C-BN system. Powder Technology 2011; 20 (5): 52–60.
[22] SP Chen, QS Meng, W Liu, ZA Munir. Titanium diboride–nickel graded materials prepared by
field-activated, pressure-assisted synthesis process. Journal of Materials Science 2009; 12 (4): 1121–
1126.
[23] L Contreras, X Turrillas, GB Vaughan, A Kvick, MA Rodriguez. Time-resolved XRD study of
TiC-TiB2 composites obtained by SHS. Acta Materialia 2004; 16 (4): 4783–4790.
[24] P Shen, BL Zou, SB Jin, QC Jiang. Reaction mechanism in self-propagating high temperature
synthesis of TiC-TiB2/Al composites from an Al-Ti-B-C system. Materials Science and Engineering
A 2007; 45 (4–5): 300–309.
[25] I Song, L Wang, M Wixom. Self-propagating high temperature synthesis and dynamic
compaction of titanium diboride/titanium carbide composites. Journal of Materials Science 2008; 12
(8): 2611-17.