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Combustion Synthesis of TiC-TiB2-Based Cermets from Elemental Powders

Combustion Synthesis of TiC-TiB2-Based Cermets from Elemental Powders Hindawi Publishing Corporation Advances in Tribology Volume 2011, Article ID 105258, 8 pages doi:10.1155/2011/105258 Research Article Combustion Synthesis of TiC-TiB -Based Cermets from Elemental Powders 1 2 2 Jun Yu, Kiyotaka Matsuura, and Munekazu Ohno Graduate School of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan Division of Materials Science and Engineering, Faculty of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan Correspondence should be addressed to Jun Yu, jeremy528@hotmail.com Received 6 June 2011; Accepted 21 July 2011 Academic Editor: Huseyin C¸imenoglu ˘ Copyright © 2011 Jun Yu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. TiC-TiB -based cermets with Ni binder were fabricated using combustion synthesis assisted by pseudohot isostatic pressing by heating the compacted powder mixture to approximately 700 C. The effects of composition on microstructure and hardness of the synthesized samples were investigated. The samples exhibited finer microstructure and higher hardness as TiC/TiB volume ratio increased and as Ni increased up to 30 vol%. A relatively high hardness value of 1950 HV was obtained for TiC-TiB - Ni(52.5/17.5/30 vol%). However, the transverse rupture strength and the modulus of elasticity values were not very high. This may be due to weak bonding strength of the interface between hard phases and Ni binder and/or insufficient densification of the samples. 1. Introduction densification, these methods involve expensive techniques and high energy consumption. To overcome the problem of Hard materials attract wide interest for their application high temperatures, a number of new densification techniques as mechanical processing equipment. Conventional hard have been investigated. For instance, reactive hot pressing materials, especially cermets based on WC, are widely used (RHP) by using displacement reactions [8] and high- for cutting tools because of their excellent hardness, high pressure self-combustion synthesis (HPCS) [9]havebeen wear resistance, and good toughness [1]. TiC-TiB -based used in a number of studies. A dense TiC-TiB -Ni cermet cermets are considered as valid candidates for the usage has been fabricated by HPCS from molten titanium with B C under extreme conditions in the light of their higher hard- and nickel of various weight percentages [10]. ness, good chemical stability, and excellent wear resistance at It is remarkable to note that the fabrication of TiC- high temperatures compared with the conventional cermets TiB -based cermets from elemental powders has not been [2]. Furthermore, from the view point of resource reserve, attempted yet. According to previous studies of our group attentions have also been directed to these tungsten-free hard [11, 12], cermets like TiC-Fe, TiB -FeAl can successfully be materials as one of alternate materials of WC-Co [3, 4]. fabricated from elemental powders. Importantly, in these In early studies, reaction sintering and hot pressing tech- processes, relatively low temperatures below 1000 Cwere niques were employed for the fabrication of TiC-TiB -based required for the highly exothermic reactions to be ignited cermets [5]. Ogwu and Davies [6] attempted to produce between elemental powders. In the present study, we investi- dense TiC-TiB -based cermets by pressureless sintering at gate the feasibility of fabrication of TiC-TiB -based cermets 1550 C for 1.5 h, by using a Ni-based binder. Singh et al. [7] with Ni binder from elemental powders, by using com- reported the fabrication of porous TiC-TiB based cermets bustion synthesis assisted by pseudohot isostatic pressure by liquid phase sintering in a hydrogen atmosphere at 1300– (pseudo-HIP). Furthermore, we examine the correlation 1350 C for 1 h with a binder system based on Ni-Mn alloys. between the composition, the synthesis process, and the Since high sintering temperatures and long sintering times or even liquid-forming additives are required to achieve full properties. 2 Advances in Tribology 2. Experimental Procedure Press Casting sand Elemental powders of titanium (45 µm in diameter and 99.4 wt% in purity), carbon (1 µm and 99.0 wt%), boron (2 µm and 99.9 wt%), and nickel (45 µm and 99.8 wt%) were thoroughly mixed with a small amount of ethanol added in To vacuum pump order to prevent segregation due to difference in the specific gravities of different kinds of powders. When preparing Compact powder mixtures,molar ratios of Ti,C,and Bwerechosen to obtain the final product with predetermined volume fractions of TiC and/or TiB . The volume fractions of TiC, TiB , and Ni binder were varied in order to investigate the effect of composition on the microstructure and mechanical properties of products. The volume fraction of Ni binder Thermocouple Heating wire was varied from 20 to 40 vol%, and the volume ratio of Figure 1: Schematic illustration of the pseudo-HIP equipment. TiC/TiB was varied as 3/1, 1/1, and 1/3. For comparison, the samples comprising only TiC or TiB and Ni binder were also prepared. The powder mixtures were pressed in a metal mold under uniaxial pressure of 640 MPa. The compacts had a cylindrical shape of a 30 mm diameter and an approximately 20 mm height. 1200 The compacts were heated by resistance wire of an Fe- Cr-Al alloy in a pseudo-HIP equipment inside a vacuum chamber shown in Figure 1. Casting sand (∼300 µmin diameter) was used as a pressing medium and as a thermal Ignition and electrical insulation material as well. The heating rate was controlled at approximately 15 C/min under an initial pseudo-HIP pressure of about 30 MPa. The pseudo-HIP pressure was immediately raised to approximately 160 MPa when a sudden temperature rise was monitored indicating the ignition of the combustion reactions, and the electricity for the heating wire was turned off. After keeping the high 0 1020304050 Heating time (min) pressure for 3 minutes, the pressure was removed, and the sample was cooled naturally inside the vacuum chamber. Figure 2: Temperature-time curve during heating of TiC-TiB - It has been reported that preheating of the compacts Ni(60/20/20) compact. before reactions has effects on reduction of porosity and hard particle size and on increase in Vickers hardness [11]. In this study, therefore, some of the compacts were preheated inside of 0.2 mm/min. Three bending experiments were performed another small vacuum chamber at a temperature of 400 C for each combustion-synthesized sample, and the results for 24 h before the combustion synthesis. were averaged. An X-ray diffraction (XRD) analysis was performed for the combustion-synthesized samples to identify the reaction products. Metallographic observations of cross sections of 3. Results and Discussion the samples were performed using an optical microscope (OM) and a scanning electron microscope (SEM) TiC and In ordertoinvestigate the effect of TiB volume fraction on TiB particle sizes were measured on the SEM images. The 2 the microstructure and mechanical properties of products, densities of the samples were measured by the Archimedes the samples with 20 vol% Ni binder were synthesized with method using pure water. The porosities were then calculated different TiB volume fractions of 0, 20, 40, 60, and 80 vol%. from the measured densities and the theoretical densities Figure 2 shows a heating curve of the sample with 60 vol% which were evaluated assuming that the samples consist of TiC and 20 vol% TiB . This sample composition is hereafter predetermined volume fraction of each phase (TiC, TiB , referred to as TiC-TiB -Ni(60/20/20) and so are the other and Ni). samples. When the compact was heated to approximately Hardness was measured by a Vickers hardness tester with 700 C, a sudden temperature rise indicating the ignition of an applied load of 50 kg and a loading time of 30 s. The combustion reactions was monitored. Figure 3 shows the transverse rupture strength (TRS) at room temperature was result of XRD analysis of TiC-TiB -Ni(60/20/20) after the measured in a three-point bending test. The test specimens reaction. On the basis of XRD analysis, no peak of pure (20 mm × 3mm × 3 mm) cut out of the sample were ground element Ti, C, and B was detected, and the sample consists of with a diamond-grinding plate and polished using diamond only TiC, TiB , and the Ni binder phase. This is also the case spay. The span width was 15 mm with a crosshead speed for the TiC-Ni(80/20) and TiC-TiB -Ni(40/40/20) samples Temperature ( C) Advances in Tribology 3 TiC-TiB -Ni(40/40/20) TiC-TiB -Ni(60/20/20) TiC-Ni(80/20) 30 35 40 45 50 55 60 65 70 75 80 85 90 0 20406080 2θ Volume fraction of TiB (vol%) TiC T = 973 K ig TiB Ni Figure 4: Relationship between T and TiB volume fraction of ad 2 samples with 20 vol% Ni. Figure 3: XRD patterns of samples with 20 vol% Ni and different volume fraction of TiC and/or TiB . as shown in Figure 3. Thus, the TiC-TiB -Ni cermets were 2 because the formation enthalpy of TiB is about 50% higher successfully synthesized from the elemental powders via the than that of TiC as specified in (2). Furthermore, when TiB reaction of is more than 50 vol%, T reaches the vaporizing point of ad Ni (3157K), and gaseous phase could exist. Then, T takes ad x + y Ti + xC+2yB+ zNi −→ xTiC + yTiB + zNi. (1) the constant value of the vaporizing point because of the absorption of heat during the evaporation of Ni, as shown It should be pointed out that the samples with higher in Figure 4.The pressure difference between the internal volume fraction of TiB , that is, TiC-TiB -Ni(20/60/20) and 2 2 part of sample and the vacuum chamber should be quite TiB -Ni(80/20) were not successfully synthesized. Instead, large, which leads to a leakage of part of the molten sample explosions occurred after the ignition of combustion reac- through the casting sand around it. Although change of T ad tions and the samples could not maintain the cylindrical is not significant in Figure 4, this could be the reason for the shape, and they were broken into some pieces, or even part of explosions. the exploded samples went through the casting sand around The SEM photographs of samples with 20 vol% Ni binder them. As a result, the investigation of microstructure and and different TiB volume fractions are shown in Figure 5. mechanical properties could not be carried out for these Hard particles can be seen clearly. These were identified samples. One may speculate that moisture was absorbed as TiC and TiB by EPMA analysis. TiC particles appear to the surfaces of the elemental powders, and it could to be nearspherical shape, while TiB particles have faceted be vaporized at the extremely high temperature due to shapes, which is in good agreement with the previous results the exothermic combustion reactions. However, considering of other researchers [15]. The average size of these hard that all the compacts were prepared by the same pro- particles in each sample was measure and the results are cedure and some of them were successfully synthesized, shown in Figure 6. Both the TiB size and TiC size increase this factor of moisture could not be the main reason for as TiB volume fraction increases. According to Figure 4, the the explosions. To find the reason for the explosions, sample with higher TiB volume fraction has higher T after 2 ad thermodynamic calculation was carried out to estimate the the combustion reactions. Hence, as TiB volume fraction adiabatic combustion temperature (T ) of each selected ad increases from 0 to 40 vol%, the sample has a higher and composition. Based on (2) shown below and the related wider temperature range for growth during cooling process, thermodynamic data [14], T was calculated assuming that ad which leads to the larger hard particle sizes. The same trend the ignition temperature for each selected composition is was also reported for the TiB -FeAl system by one of the 700 C according to the heating curve shown in Figure 2: present authors, in which the TiB size decreased as FeAl volume fraction increased [11]. Ti + C = TiC, ΔH =−184.1kJ/mol, The relative densities were measured, and the results are (2) shown in Figure 7. The density decreases as TiB increases Ti + 2B = TiB , ΔH =−279.5kJ/mol. 2 f from 20 to 40 vol%. As mentioned above, the increase of Figure 4 shows the relationship between the calculated TiB volume fraction results in high T which causes a 2 ad T and TiB volume fraction of samples with 20 vol% high pressure inside the sample, and hence, the densification ad 2 Ni binder. T increases as TiB volume fraction increases, of the sample becomes difficult under a fixed pseudo-HIP ad 2 Intensity Adiabatic combustion temperature (T ) (K) ad 4 Advances in Tribology Ni TiB TiB TiC TiC TiC Ni Ni COMP COMP COMP 5 μm 10 μm 10 μm 10 μm 10 μm 10 μm XM3180 XM3186 15.0 kV 15.0 kV XM3610 15.0 kV ×3, 000 ×1, 500 ×1, 500 (a) (b) (c) Figure 5: SEM photographs of samples with 20 vol% Ni and different volume fraction of TiC and/or TiB . (a) TiC-Ni(80/20), (b) TiC-TiB - 2 2 Ni(60/20/20), and (c) TiC-TiB -Ni(40/40/20). 9 2000 100 600 50 020 40 Volume fraction of TiB (vol%) 020 40 Volume fraction of TiB (vol%) Vickers hardness Relative density TiC TiB Figure 7: Effect of TiB volume fraction on relative density and Figure 6: Effect of TiB volume fraction on average particle size of Vickers hardness of samples with 20 vol% Ni. samples with 20 vol% Ni. former sample. Therefore, the densification is quite essential load. However, as shown in Figure 7, the sample with no to obtain good hardness. TiB has a lower relative density than the TiC-TiB -Ni(60/ In order to investigate the effect of Ni volume fraction on 2 2 20/20), though it has a lower T . The reason for the lower the microstructure and mechanical properties of products, ad relative density or higher porosity should be a larger amount the samples with different Ni volume fractions of 20, 30, and of moisture absorbed on surfaces of carbon powders. The 40 vol% were synthesized with the fixed TiC/TiB volume carbon powder used in the present study has smaller size and ratio of 3/1. Figure 8 shows the SEM photographs of this larger specific surface area than boron powder, and hence, series of samples. Figure 9 shows the relationship between the usage of large amount of the carbon powders incurs T and Ni volume fraction. Furthermore, the dependence of ad the problem with the moistures in the present experiments. the particle size on the Ni volume fraction is demonstrated The Vickers hardness of samples is also shown in Figure 7. in Figure 10. The same variation tendency of hard particle The hardness has the same variation tendency as the size versus T is observed as is consistent with the above- ad relative density. Generally, it is considered that the TiC-TiB - mentioned explanation. The increase in Ni binder reduces Ni(40/40/20) should exhibit higher hardness than the TiC- T (Figure 9) and narrows the solidification temperature ad TiB -Ni(60/20/20) based on the rule of mixtures, because range, which leads to smaller particle sizes (Figure 10). the former sample has higher fraction of the harder phase The relative densities of samples are shown in Figure 11 TiB . However, the former sample exhibits lower hardness with the result of the Vickers hardness. The relative density than the latter one which is due to the high porosity in the was improved as the volume fraction of Ni binder was TiC and TiB particle size (μm) Vickers hardness (HV) Relative density (%) Advances in Tribology 5 TiB Ni Ni TiB TiB TiC Ni TiC TiC COMP COMP 10 μm COMP 10 μm 10 μm 10 μm 10 μm 10 μm XM3186 15.0 kV ×1, 500 ×1, 500 XM6068 ×2, 000 XM3622 15.0 kV 15.0 kV (a) (b) (c) Figure 8: SEM photographs of samples with TiC/TiB ratio of 3/1 and 20, 30, 40 vol% Ni, respectively. (a) TiC-TiB -Ni(60/20/20), (b) 2 2 TiC-TiB -Ni(52.5/17.5/30), and (c) TiC-TiB -Ni(45/15/40). 2 2 30 40 20 30 40 Volume fraction of Ni (vol%) Volume fraction of Ni (vol%) TiC T = 973 K ig TiB Figure 9: Relationship between T and Ni volume fraction of ad Figure 10: Effect of Ni volume fraction on average particle size of samples with a TiC/TiB volume ratio of 3/1. 2 samples with a TiC/TiB ratio of 3/1. increased, which further confirms our explanation that an extremely high thermal energy generated from combustion reactions is not preferable for complete densification because it causes a huge pressure difference between the internal and external parts of the sample. As a result of the increase in relative density, Vickers hardness values increased from 1700 HV to 1850 HV as Ni binder increased from 20 to 30 vol%. However, the hardness decreased significantly as Ni binder increased to 40 vol%, although it was relatively dense. This fact indicates that in order to obtain hard cermets, the amount of hard particles is an important factor, which is also well known as the rule of mixtures. It is 20 30 40 important to take a balance of the relative density and the Volume fraction of Ni (vol.%) hardness into account in determining the composition of Vickers hardness samples. Relative density According to our previous work on the TiB -FeAl system [11], preheating of the compact at a temperature below Figure 11: Effect of Ni volume fraction on relative density and the ignition temperature of combustion synthesis reactions Vickers hardness of samples with a TiC/TiB ratio of 3/1. Adiabatic combustion temperature (T ) (K) ad Vickers hardness (HV) TiC and TiB particle size (μm) Relative density (%) 6 Advances in Tribology 1mm 1mm (a) (b) 1mm 1mm (c) (d) Figure 12: OM photographs of samples of TiC-TiB -Ni(52.5/17.5/30), (a) without preheating and (c) with preheating at 400 Cfor 24h, respectively. The monochrome images of (a) and (c) are shown in (b) and (d), respectively, in which the black area approximately reflects the pores by image process using Canvas software. can bring about the reduction in hard particle size and Table 1: Comparison of mechanical properties between the sample in the present work (A) and that in literature (B) [13]. porosity and increase in Vickers hardness of the sample. In the present work, to obtain a sample with both high hardness and high relative density, the preheating of the Relative HV TRS Sample Composition density (%) (kg/mm ) (MPa) compact of TiC-TiB -Ni(52.5/17.5/30) was carried out at 400 C for 24 h before the combustion synthesis. The effect TiC-TiB -Ni of preheating on the densification is shown in the optical 96.95 1950 330 (52.5/17.5/30) vol.% microscopy (OM) photographs in Figure 12. The sample with preheating shows less porosity. Moreover, the density TiC-TiN-WC-Mo-Ni-C increased from 93.45 to 96.95%, and the hardness increased 99.98 1750 1521 (40/10/15/14/20/1) wt.% from 1850 HV to 1950 HV by the preheating treatment. The reason for the decrease in porosity due to the preheating can be explained as follows. Some intermetallic compounds were formed by solid-state reactions during preheating were synthesized. The transverse rupture strength (TRS) and between different elemental powders. This formation of the the modulus of elasticity (E) were calculated according to, compounds reduces total amount of heat generation by the 3 LF subsequent combustion reactions. Hence, the combustion TRS = · , temperature is relatively lowered. This is effective for a WT (3) better densification. However, unlike the previous work, the L F decrease in the hard particle size due to preheating cannot be E = · , Δl 4WT found in the present work. This may be because we chose a relatively lower preheating temperature that limited the where L is the span width in the bending test, F the load, W solid-state reactions during preheating. the length of the specimen, T the thickness of the specimen, The bending test was carried out only for the sample and Δl the crosshead distance until fracture. The calculated TiC-TiB -Ni(52.5/17.5/30) with preheating, which has the results of TRS and E were approximately 330 MPa and highest relative density of 96.95% among all the samples that 74 GPa, respectively. Table 1 shows the comparison between Advances in Tribology 7 As the composition of powder mixture influences the combustion temperature as well as the densification, it has considerable effects on microstructure and mechanical properties of synthesized samples. When the volume fraction of Ni binder is 20 vol%, the finer microstructure and higher hardness were observed for the higher TiC/TiB ratio. In Pore the samples with the TiC/TiB volume ratio of 3 : 1, the relative density increases with the volume fraction of Ni. The hardness increases as Ni increased from 20 to 30 vol%, but it decreases as Ni increases to 40 vol%. TiC-TiB - 10 μm Pore Ni(52.5/17.5/30) exhibited high relative density of 93.45% and high hardness of 1850 HV. Figure 13: SEM photograph of fractured surface after three-point The preheating treatment of the compacted powder bending test of the specimen of TiC-TiB -Ni(52.5/17.5/30) with mixture was quite effective for the densification of TiC-TiB - preheating. Ni(52.5/17.5/30). The relative density increased from 93.45 to 96.95% by preheating at 400 C for 24 h in vacuum. As a result, the hardness increased from 1850 HV to 1950 HV. the mechanical properties of the present sample and the However, the refinement of hard particle size due to the conventional cermet used for cutting tools. The value of preheating was not observed in the present work. TRS in the present sample is much lower than the one in The transverse rupture strength of the present sample the conventional cermet. There are several possible reasons was not very high, which is considered attributable to weak for the low values of TRS obtained in the present work. bonding strength of the interface between hard phase and Ni Figure 13 shows the SEM photograph of fracture surface after binder and insufficient densification. the bending test. It can be clearly seen that the fracture of specimen was almost caused by intergranular rupture. The hard particle sizes in the present sample are in the range of References 2–4 µm which are relatively coarse. The fracture of cermets with coarse grains generally tends to occur by transcrystalline [1] B. R. Sunil, D. Sivaprahasam, and R. Subasri, “Microwave rupture [16]. That is to say, the bonding strength of the sintering of nanocrystalline WC-12Co: challenges and per- phase interface should be significantly weak in the present spectives,” International Journal of Refractory Metals and Hard sample. It can also be seen that a large-sized pore exists on the Materials, vol. 28, no. 2, pp. 180–186, 2010. fractured surface in Figure 13, although the relative density [2] T. J. Davies and A. A. Ogwu, “Characterisation of composite of of 96.95% is the highest in the present study. The existence TiC + TiB bonded with nickel based binder alloy: mechanical of the large pores could be one of the reasons for low and microstructural properties,” Powder Metallurgy, vol. 38, strength. Furthermore, although the surface of specimens no. 1, pp. 39–44, 1995. was well ground and polished before the bending test, it [3] M. X. Gao, F. J. Oliveira, Y. Pan, L. Yang, J. L. Baptista, and J. M. Vieira, “Strength improvement and fracture mechanism could be inferred that there were pores on the surfaces of in Fe40Al/TiC composites with high content of TiC,” Inter- the specimens and they would weaken the TRS due to stress metallics, vol. 13, no. 5, pp. 460–466, 2005. concentration. It is also possible that the contamination on [4] M. Krasnowski, A. Witek, and T. Kulik, “The FeAl-30%TiC the surfaces of starting powders decreased the wettability nanocomposite produced by mechanical alloying and hot- between Ni binder and hard particles. In recent studies on pressing consolidation,” Intermetallics, vol. 10, no. 4, pp. 371– combustion synthesis [16, 17], some elements are added 376, 2002. to the starting powders in order to increase the wettability [5] S. K. Bhaumik, C. Divakar, A. K. Singh, and G. S. Upadhyaya, between hard phase and binder. For instance, Molybdenum “Synthesis and sintering of TiB and TiB -TiC composite 2 2 is often added to the starting powders in order to obtain a under high pressure,” Materials Science and Engineering A, vol. good wetting of TiC, TiN, with Ni. Therefore, it is expected 279, no. 1-2, pp. 275–281, 2000. that the addition of some elements for improving the [6] A. A. Ogwu and T. J. Davies, “The densification and mechan- wettability yields better mechanical properties of the present ical properties of a TiC and TiB hardmetal sintered with a reactive alloy binder,” Physica Status Solidi (A), vol. 153, no. 1, sample. This attempt remains as a future work. pp. 101–116, 1996. [7] M. Singh, K. N. Rai, and G. S. Upadhyaya, “Sintered porous 4. Conclusions cermets based on TiB and TiB -TiC-Mo C,” Materials Chem- 2 2 2 istry and Physics, vol. 67, no. 1-3, pp. 226–233, 2001. TiC-TiB -based cermets with Ni binder can be successfully [8] C. H. Henager Jr., J. L. Brimhall, and J. P. Hirth, “Synthesis of fabricated by combustion synthesis assisted by pseudo- aMoSi SiC composite in situ using a solid state displacement HIP from elemental starting powders. As a result of the reaction,” Materials Science and Engineering A, vol. 155, no. 1- exothermic reactions between elemental starting powders, 2, pp. 109–114, 1992. the process of combustion synthesis can be self-propagated [9] Z.Y.Fu, H. Wang,W.M.Wang, andR.Z.Yuan, “Composites after heating the compacted powder mixture to approx- fabricated by self-propagating high-temperature synthesis,” imately 700 C, which is much lower than the synthesis Journal of Materials Processing Technology, vol. 137, no. 1–3, temperature in conventional processes. pp. 30–34, 2003. 8 Advances in Tribology [10] D. Vallauri and F. A. Deorsola, “Synthesis of TiC-TiB2- Ni cermets by thermal explosion under pressure,” Materials Research Bulletin, vol. 44, no. 7, pp. 1528–1533, 2009. [11] K. Matsuura, Y. Obara, and K. Kojima, “Combustion synthesis of boride particle dispersed hard metal from elemental powders,” International Journal of Refractory Metals and Hard Materials, vol. 27, no. 2, pp. 376–381, 2009. [12] K. Matsuura, Y. Obara, and M. Kudoh, “Fabrication of TiB2 particle dispersed FeAl-based composites by self-propagating high-temperature synthesis,” ISIJ International, vol. 46, no. 6, pp. 871–874, 2006. [13] X. Zhang and N. Liu, “Microstructure, mechanical properties and thermal shock resistance of nano-TiN modified TiC- based cermets with different binders,” International Journal of Refractory Metals and Hard Materials, vol. 26, no. 6, pp. 575– 582, 2008. [14] M. Binnewies and E. Mike, Thermochemical Data of Elements and Compounds, Wiley-VCH, 2002. [15] D. Vallauri,I.C.At´ıas Adrian, ´ and A. Chrysanthou, “TiC-TiB2 composites: a review of phase relationships, processing and properties,” Journal of the European Ceramic Society, vol. 28, no. 8, pp. 1697–1713, 2008. [16] N. Liu, W. Yin, and L. Zhu, “Effect of TiC/TiN powder size on microstructure and properties of Ti(C, N)-based cermets,” Materials Science and Engineering A, vol. 445-446, pp. 707– 716, 2007. [17] S. Cardinal, A. Malcher ` e, V. Garnier, and G. Fantozzi, “Microstructure and mechanical properties of TiC-TiN based cermets for tools application,” International Journal of Refrac- tory Metals and Hard Materials, vol. 27, no. 3, pp. 521–527, 2009. 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Combustion Synthesis of TiC-TiB2-Based Cermets from Elemental Powders

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Hindawi Publishing Corporation
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Copyright © 2011 Jun Yu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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1687-5915
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1687-5923
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10.1155/2011/105258
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Abstract

Hindawi Publishing Corporation Advances in Tribology Volume 2011, Article ID 105258, 8 pages doi:10.1155/2011/105258 Research Article Combustion Synthesis of TiC-TiB -Based Cermets from Elemental Powders 1 2 2 Jun Yu, Kiyotaka Matsuura, and Munekazu Ohno Graduate School of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan Division of Materials Science and Engineering, Faculty of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan Correspondence should be addressed to Jun Yu, jeremy528@hotmail.com Received 6 June 2011; Accepted 21 July 2011 Academic Editor: Huseyin C¸imenoglu ˘ Copyright © 2011 Jun Yu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. TiC-TiB -based cermets with Ni binder were fabricated using combustion synthesis assisted by pseudohot isostatic pressing by heating the compacted powder mixture to approximately 700 C. The effects of composition on microstructure and hardness of the synthesized samples were investigated. The samples exhibited finer microstructure and higher hardness as TiC/TiB volume ratio increased and as Ni increased up to 30 vol%. A relatively high hardness value of 1950 HV was obtained for TiC-TiB - Ni(52.5/17.5/30 vol%). However, the transverse rupture strength and the modulus of elasticity values were not very high. This may be due to weak bonding strength of the interface between hard phases and Ni binder and/or insufficient densification of the samples. 1. Introduction densification, these methods involve expensive techniques and high energy consumption. To overcome the problem of Hard materials attract wide interest for their application high temperatures, a number of new densification techniques as mechanical processing equipment. Conventional hard have been investigated. For instance, reactive hot pressing materials, especially cermets based on WC, are widely used (RHP) by using displacement reactions [8] and high- for cutting tools because of their excellent hardness, high pressure self-combustion synthesis (HPCS) [9]havebeen wear resistance, and good toughness [1]. TiC-TiB -based used in a number of studies. A dense TiC-TiB -Ni cermet cermets are considered as valid candidates for the usage has been fabricated by HPCS from molten titanium with B C under extreme conditions in the light of their higher hard- and nickel of various weight percentages [10]. ness, good chemical stability, and excellent wear resistance at It is remarkable to note that the fabrication of TiC- high temperatures compared with the conventional cermets TiB -based cermets from elemental powders has not been [2]. Furthermore, from the view point of resource reserve, attempted yet. According to previous studies of our group attentions have also been directed to these tungsten-free hard [11, 12], cermets like TiC-Fe, TiB -FeAl can successfully be materials as one of alternate materials of WC-Co [3, 4]. fabricated from elemental powders. Importantly, in these In early studies, reaction sintering and hot pressing tech- processes, relatively low temperatures below 1000 Cwere niques were employed for the fabrication of TiC-TiB -based required for the highly exothermic reactions to be ignited cermets [5]. Ogwu and Davies [6] attempted to produce between elemental powders. In the present study, we investi- dense TiC-TiB -based cermets by pressureless sintering at gate the feasibility of fabrication of TiC-TiB -based cermets 1550 C for 1.5 h, by using a Ni-based binder. Singh et al. [7] with Ni binder from elemental powders, by using com- reported the fabrication of porous TiC-TiB based cermets bustion synthesis assisted by pseudohot isostatic pressure by liquid phase sintering in a hydrogen atmosphere at 1300– (pseudo-HIP). Furthermore, we examine the correlation 1350 C for 1 h with a binder system based on Ni-Mn alloys. between the composition, the synthesis process, and the Since high sintering temperatures and long sintering times or even liquid-forming additives are required to achieve full properties. 2 Advances in Tribology 2. Experimental Procedure Press Casting sand Elemental powders of titanium (45 µm in diameter and 99.4 wt% in purity), carbon (1 µm and 99.0 wt%), boron (2 µm and 99.9 wt%), and nickel (45 µm and 99.8 wt%) were thoroughly mixed with a small amount of ethanol added in To vacuum pump order to prevent segregation due to difference in the specific gravities of different kinds of powders. When preparing Compact powder mixtures,molar ratios of Ti,C,and Bwerechosen to obtain the final product with predetermined volume fractions of TiC and/or TiB . The volume fractions of TiC, TiB , and Ni binder were varied in order to investigate the effect of composition on the microstructure and mechanical properties of products. The volume fraction of Ni binder Thermocouple Heating wire was varied from 20 to 40 vol%, and the volume ratio of Figure 1: Schematic illustration of the pseudo-HIP equipment. TiC/TiB was varied as 3/1, 1/1, and 1/3. For comparison, the samples comprising only TiC or TiB and Ni binder were also prepared. The powder mixtures were pressed in a metal mold under uniaxial pressure of 640 MPa. The compacts had a cylindrical shape of a 30 mm diameter and an approximately 20 mm height. 1200 The compacts were heated by resistance wire of an Fe- Cr-Al alloy in a pseudo-HIP equipment inside a vacuum chamber shown in Figure 1. Casting sand (∼300 µmin diameter) was used as a pressing medium and as a thermal Ignition and electrical insulation material as well. The heating rate was controlled at approximately 15 C/min under an initial pseudo-HIP pressure of about 30 MPa. The pseudo-HIP pressure was immediately raised to approximately 160 MPa when a sudden temperature rise was monitored indicating the ignition of the combustion reactions, and the electricity for the heating wire was turned off. After keeping the high 0 1020304050 Heating time (min) pressure for 3 minutes, the pressure was removed, and the sample was cooled naturally inside the vacuum chamber. Figure 2: Temperature-time curve during heating of TiC-TiB - It has been reported that preheating of the compacts Ni(60/20/20) compact. before reactions has effects on reduction of porosity and hard particle size and on increase in Vickers hardness [11]. In this study, therefore, some of the compacts were preheated inside of 0.2 mm/min. Three bending experiments were performed another small vacuum chamber at a temperature of 400 C for each combustion-synthesized sample, and the results for 24 h before the combustion synthesis. were averaged. An X-ray diffraction (XRD) analysis was performed for the combustion-synthesized samples to identify the reaction products. Metallographic observations of cross sections of 3. Results and Discussion the samples were performed using an optical microscope (OM) and a scanning electron microscope (SEM) TiC and In ordertoinvestigate the effect of TiB volume fraction on TiB particle sizes were measured on the SEM images. The 2 the microstructure and mechanical properties of products, densities of the samples were measured by the Archimedes the samples with 20 vol% Ni binder were synthesized with method using pure water. The porosities were then calculated different TiB volume fractions of 0, 20, 40, 60, and 80 vol%. from the measured densities and the theoretical densities Figure 2 shows a heating curve of the sample with 60 vol% which were evaluated assuming that the samples consist of TiC and 20 vol% TiB . This sample composition is hereafter predetermined volume fraction of each phase (TiC, TiB , referred to as TiC-TiB -Ni(60/20/20) and so are the other and Ni). samples. When the compact was heated to approximately Hardness was measured by a Vickers hardness tester with 700 C, a sudden temperature rise indicating the ignition of an applied load of 50 kg and a loading time of 30 s. The combustion reactions was monitored. Figure 3 shows the transverse rupture strength (TRS) at room temperature was result of XRD analysis of TiC-TiB -Ni(60/20/20) after the measured in a three-point bending test. The test specimens reaction. On the basis of XRD analysis, no peak of pure (20 mm × 3mm × 3 mm) cut out of the sample were ground element Ti, C, and B was detected, and the sample consists of with a diamond-grinding plate and polished using diamond only TiC, TiB , and the Ni binder phase. This is also the case spay. The span width was 15 mm with a crosshead speed for the TiC-Ni(80/20) and TiC-TiB -Ni(40/40/20) samples Temperature ( C) Advances in Tribology 3 TiC-TiB -Ni(40/40/20) TiC-TiB -Ni(60/20/20) TiC-Ni(80/20) 30 35 40 45 50 55 60 65 70 75 80 85 90 0 20406080 2θ Volume fraction of TiB (vol%) TiC T = 973 K ig TiB Ni Figure 4: Relationship between T and TiB volume fraction of ad 2 samples with 20 vol% Ni. Figure 3: XRD patterns of samples with 20 vol% Ni and different volume fraction of TiC and/or TiB . as shown in Figure 3. Thus, the TiC-TiB -Ni cermets were 2 because the formation enthalpy of TiB is about 50% higher successfully synthesized from the elemental powders via the than that of TiC as specified in (2). Furthermore, when TiB reaction of is more than 50 vol%, T reaches the vaporizing point of ad Ni (3157K), and gaseous phase could exist. Then, T takes ad x + y Ti + xC+2yB+ zNi −→ xTiC + yTiB + zNi. (1) the constant value of the vaporizing point because of the absorption of heat during the evaporation of Ni, as shown It should be pointed out that the samples with higher in Figure 4.The pressure difference between the internal volume fraction of TiB , that is, TiC-TiB -Ni(20/60/20) and 2 2 part of sample and the vacuum chamber should be quite TiB -Ni(80/20) were not successfully synthesized. Instead, large, which leads to a leakage of part of the molten sample explosions occurred after the ignition of combustion reac- through the casting sand around it. Although change of T ad tions and the samples could not maintain the cylindrical is not significant in Figure 4, this could be the reason for the shape, and they were broken into some pieces, or even part of explosions. the exploded samples went through the casting sand around The SEM photographs of samples with 20 vol% Ni binder them. As a result, the investigation of microstructure and and different TiB volume fractions are shown in Figure 5. mechanical properties could not be carried out for these Hard particles can be seen clearly. These were identified samples. One may speculate that moisture was absorbed as TiC and TiB by EPMA analysis. TiC particles appear to the surfaces of the elemental powders, and it could to be nearspherical shape, while TiB particles have faceted be vaporized at the extremely high temperature due to shapes, which is in good agreement with the previous results the exothermic combustion reactions. However, considering of other researchers [15]. The average size of these hard that all the compacts were prepared by the same pro- particles in each sample was measure and the results are cedure and some of them were successfully synthesized, shown in Figure 6. Both the TiB size and TiC size increase this factor of moisture could not be the main reason for as TiB volume fraction increases. According to Figure 4, the the explosions. To find the reason for the explosions, sample with higher TiB volume fraction has higher T after 2 ad thermodynamic calculation was carried out to estimate the the combustion reactions. Hence, as TiB volume fraction adiabatic combustion temperature (T ) of each selected ad increases from 0 to 40 vol%, the sample has a higher and composition. Based on (2) shown below and the related wider temperature range for growth during cooling process, thermodynamic data [14], T was calculated assuming that ad which leads to the larger hard particle sizes. The same trend the ignition temperature for each selected composition is was also reported for the TiB -FeAl system by one of the 700 C according to the heating curve shown in Figure 2: present authors, in which the TiB size decreased as FeAl volume fraction increased [11]. Ti + C = TiC, ΔH =−184.1kJ/mol, The relative densities were measured, and the results are (2) shown in Figure 7. The density decreases as TiB increases Ti + 2B = TiB , ΔH =−279.5kJ/mol. 2 f from 20 to 40 vol%. As mentioned above, the increase of Figure 4 shows the relationship between the calculated TiB volume fraction results in high T which causes a 2 ad T and TiB volume fraction of samples with 20 vol% high pressure inside the sample, and hence, the densification ad 2 Ni binder. T increases as TiB volume fraction increases, of the sample becomes difficult under a fixed pseudo-HIP ad 2 Intensity Adiabatic combustion temperature (T ) (K) ad 4 Advances in Tribology Ni TiB TiB TiC TiC TiC Ni Ni COMP COMP COMP 5 μm 10 μm 10 μm 10 μm 10 μm 10 μm XM3180 XM3186 15.0 kV 15.0 kV XM3610 15.0 kV ×3, 000 ×1, 500 ×1, 500 (a) (b) (c) Figure 5: SEM photographs of samples with 20 vol% Ni and different volume fraction of TiC and/or TiB . (a) TiC-Ni(80/20), (b) TiC-TiB - 2 2 Ni(60/20/20), and (c) TiC-TiB -Ni(40/40/20). 9 2000 100 600 50 020 40 Volume fraction of TiB (vol%) 020 40 Volume fraction of TiB (vol%) Vickers hardness Relative density TiC TiB Figure 7: Effect of TiB volume fraction on relative density and Figure 6: Effect of TiB volume fraction on average particle size of Vickers hardness of samples with 20 vol% Ni. samples with 20 vol% Ni. former sample. Therefore, the densification is quite essential load. However, as shown in Figure 7, the sample with no to obtain good hardness. TiB has a lower relative density than the TiC-TiB -Ni(60/ In order to investigate the effect of Ni volume fraction on 2 2 20/20), though it has a lower T . The reason for the lower the microstructure and mechanical properties of products, ad relative density or higher porosity should be a larger amount the samples with different Ni volume fractions of 20, 30, and of moisture absorbed on surfaces of carbon powders. The 40 vol% were synthesized with the fixed TiC/TiB volume carbon powder used in the present study has smaller size and ratio of 3/1. Figure 8 shows the SEM photographs of this larger specific surface area than boron powder, and hence, series of samples. Figure 9 shows the relationship between the usage of large amount of the carbon powders incurs T and Ni volume fraction. Furthermore, the dependence of ad the problem with the moistures in the present experiments. the particle size on the Ni volume fraction is demonstrated The Vickers hardness of samples is also shown in Figure 7. in Figure 10. The same variation tendency of hard particle The hardness has the same variation tendency as the size versus T is observed as is consistent with the above- ad relative density. Generally, it is considered that the TiC-TiB - mentioned explanation. The increase in Ni binder reduces Ni(40/40/20) should exhibit higher hardness than the TiC- T (Figure 9) and narrows the solidification temperature ad TiB -Ni(60/20/20) based on the rule of mixtures, because range, which leads to smaller particle sizes (Figure 10). the former sample has higher fraction of the harder phase The relative densities of samples are shown in Figure 11 TiB . However, the former sample exhibits lower hardness with the result of the Vickers hardness. The relative density than the latter one which is due to the high porosity in the was improved as the volume fraction of Ni binder was TiC and TiB particle size (μm) Vickers hardness (HV) Relative density (%) Advances in Tribology 5 TiB Ni Ni TiB TiB TiC Ni TiC TiC COMP COMP 10 μm COMP 10 μm 10 μm 10 μm 10 μm 10 μm XM3186 15.0 kV ×1, 500 ×1, 500 XM6068 ×2, 000 XM3622 15.0 kV 15.0 kV (a) (b) (c) Figure 8: SEM photographs of samples with TiC/TiB ratio of 3/1 and 20, 30, 40 vol% Ni, respectively. (a) TiC-TiB -Ni(60/20/20), (b) 2 2 TiC-TiB -Ni(52.5/17.5/30), and (c) TiC-TiB -Ni(45/15/40). 2 2 30 40 20 30 40 Volume fraction of Ni (vol%) Volume fraction of Ni (vol%) TiC T = 973 K ig TiB Figure 9: Relationship between T and Ni volume fraction of ad Figure 10: Effect of Ni volume fraction on average particle size of samples with a TiC/TiB volume ratio of 3/1. 2 samples with a TiC/TiB ratio of 3/1. increased, which further confirms our explanation that an extremely high thermal energy generated from combustion reactions is not preferable for complete densification because it causes a huge pressure difference between the internal and external parts of the sample. As a result of the increase in relative density, Vickers hardness values increased from 1700 HV to 1850 HV as Ni binder increased from 20 to 30 vol%. However, the hardness decreased significantly as Ni binder increased to 40 vol%, although it was relatively dense. This fact indicates that in order to obtain hard cermets, the amount of hard particles is an important factor, which is also well known as the rule of mixtures. It is 20 30 40 important to take a balance of the relative density and the Volume fraction of Ni (vol.%) hardness into account in determining the composition of Vickers hardness samples. Relative density According to our previous work on the TiB -FeAl system [11], preheating of the compact at a temperature below Figure 11: Effect of Ni volume fraction on relative density and the ignition temperature of combustion synthesis reactions Vickers hardness of samples with a TiC/TiB ratio of 3/1. Adiabatic combustion temperature (T ) (K) ad Vickers hardness (HV) TiC and TiB particle size (μm) Relative density (%) 6 Advances in Tribology 1mm 1mm (a) (b) 1mm 1mm (c) (d) Figure 12: OM photographs of samples of TiC-TiB -Ni(52.5/17.5/30), (a) without preheating and (c) with preheating at 400 Cfor 24h, respectively. The monochrome images of (a) and (c) are shown in (b) and (d), respectively, in which the black area approximately reflects the pores by image process using Canvas software. can bring about the reduction in hard particle size and Table 1: Comparison of mechanical properties between the sample in the present work (A) and that in literature (B) [13]. porosity and increase in Vickers hardness of the sample. In the present work, to obtain a sample with both high hardness and high relative density, the preheating of the Relative HV TRS Sample Composition density (%) (kg/mm ) (MPa) compact of TiC-TiB -Ni(52.5/17.5/30) was carried out at 400 C for 24 h before the combustion synthesis. The effect TiC-TiB -Ni of preheating on the densification is shown in the optical 96.95 1950 330 (52.5/17.5/30) vol.% microscopy (OM) photographs in Figure 12. The sample with preheating shows less porosity. Moreover, the density TiC-TiN-WC-Mo-Ni-C increased from 93.45 to 96.95%, and the hardness increased 99.98 1750 1521 (40/10/15/14/20/1) wt.% from 1850 HV to 1950 HV by the preheating treatment. The reason for the decrease in porosity due to the preheating can be explained as follows. Some intermetallic compounds were formed by solid-state reactions during preheating were synthesized. The transverse rupture strength (TRS) and between different elemental powders. This formation of the the modulus of elasticity (E) were calculated according to, compounds reduces total amount of heat generation by the 3 LF subsequent combustion reactions. Hence, the combustion TRS = · , temperature is relatively lowered. This is effective for a WT (3) better densification. However, unlike the previous work, the L F decrease in the hard particle size due to preheating cannot be E = · , Δl 4WT found in the present work. This may be because we chose a relatively lower preheating temperature that limited the where L is the span width in the bending test, F the load, W solid-state reactions during preheating. the length of the specimen, T the thickness of the specimen, The bending test was carried out only for the sample and Δl the crosshead distance until fracture. The calculated TiC-TiB -Ni(52.5/17.5/30) with preheating, which has the results of TRS and E were approximately 330 MPa and highest relative density of 96.95% among all the samples that 74 GPa, respectively. Table 1 shows the comparison between Advances in Tribology 7 As the composition of powder mixture influences the combustion temperature as well as the densification, it has considerable effects on microstructure and mechanical properties of synthesized samples. When the volume fraction of Ni binder is 20 vol%, the finer microstructure and higher hardness were observed for the higher TiC/TiB ratio. In Pore the samples with the TiC/TiB volume ratio of 3 : 1, the relative density increases with the volume fraction of Ni. The hardness increases as Ni increased from 20 to 30 vol%, but it decreases as Ni increases to 40 vol%. TiC-TiB - 10 μm Pore Ni(52.5/17.5/30) exhibited high relative density of 93.45% and high hardness of 1850 HV. Figure 13: SEM photograph of fractured surface after three-point The preheating treatment of the compacted powder bending test of the specimen of TiC-TiB -Ni(52.5/17.5/30) with mixture was quite effective for the densification of TiC-TiB - preheating. Ni(52.5/17.5/30). The relative density increased from 93.45 to 96.95% by preheating at 400 C for 24 h in vacuum. As a result, the hardness increased from 1850 HV to 1950 HV. the mechanical properties of the present sample and the However, the refinement of hard particle size due to the conventional cermet used for cutting tools. The value of preheating was not observed in the present work. TRS in the present sample is much lower than the one in The transverse rupture strength of the present sample the conventional cermet. There are several possible reasons was not very high, which is considered attributable to weak for the low values of TRS obtained in the present work. bonding strength of the interface between hard phase and Ni Figure 13 shows the SEM photograph of fracture surface after binder and insufficient densification. the bending test. It can be clearly seen that the fracture of specimen was almost caused by intergranular rupture. The hard particle sizes in the present sample are in the range of References 2–4 µm which are relatively coarse. The fracture of cermets with coarse grains generally tends to occur by transcrystalline [1] B. R. Sunil, D. Sivaprahasam, and R. Subasri, “Microwave rupture [16]. That is to say, the bonding strength of the sintering of nanocrystalline WC-12Co: challenges and per- phase interface should be significantly weak in the present spectives,” International Journal of Refractory Metals and Hard sample. It can also be seen that a large-sized pore exists on the Materials, vol. 28, no. 2, pp. 180–186, 2010. fractured surface in Figure 13, although the relative density [2] T. J. Davies and A. A. Ogwu, “Characterisation of composite of of 96.95% is the highest in the present study. The existence TiC + TiB bonded with nickel based binder alloy: mechanical of the large pores could be one of the reasons for low and microstructural properties,” Powder Metallurgy, vol. 38, strength. Furthermore, although the surface of specimens no. 1, pp. 39–44, 1995. was well ground and polished before the bending test, it [3] M. X. Gao, F. J. Oliveira, Y. Pan, L. Yang, J. L. Baptista, and J. M. Vieira, “Strength improvement and fracture mechanism could be inferred that there were pores on the surfaces of in Fe40Al/TiC composites with high content of TiC,” Inter- the specimens and they would weaken the TRS due to stress metallics, vol. 13, no. 5, pp. 460–466, 2005. concentration. It is also possible that the contamination on [4] M. Krasnowski, A. Witek, and T. Kulik, “The FeAl-30%TiC the surfaces of starting powders decreased the wettability nanocomposite produced by mechanical alloying and hot- between Ni binder and hard particles. In recent studies on pressing consolidation,” Intermetallics, vol. 10, no. 4, pp. 371– combustion synthesis [16, 17], some elements are added 376, 2002. to the starting powders in order to increase the wettability [5] S. K. Bhaumik, C. Divakar, A. K. Singh, and G. S. Upadhyaya, between hard phase and binder. For instance, Molybdenum “Synthesis and sintering of TiB and TiB -TiC composite 2 2 is often added to the starting powders in order to obtain a under high pressure,” Materials Science and Engineering A, vol. good wetting of TiC, TiN, with Ni. Therefore, it is expected 279, no. 1-2, pp. 275–281, 2000. that the addition of some elements for improving the [6] A. A. Ogwu and T. J. Davies, “The densification and mechan- wettability yields better mechanical properties of the present ical properties of a TiC and TiB hardmetal sintered with a reactive alloy binder,” Physica Status Solidi (A), vol. 153, no. 1, sample. This attempt remains as a future work. pp. 101–116, 1996. [7] M. Singh, K. N. Rai, and G. S. Upadhyaya, “Sintered porous 4. Conclusions cermets based on TiB and TiB -TiC-Mo C,” Materials Chem- 2 2 2 istry and Physics, vol. 67, no. 1-3, pp. 226–233, 2001. TiC-TiB -based cermets with Ni binder can be successfully [8] C. H. Henager Jr., J. L. Brimhall, and J. P. Hirth, “Synthesis of fabricated by combustion synthesis assisted by pseudo- aMoSi SiC composite in situ using a solid state displacement HIP from elemental starting powders. As a result of the reaction,” Materials Science and Engineering A, vol. 155, no. 1- exothermic reactions between elemental starting powders, 2, pp. 109–114, 1992. the process of combustion synthesis can be self-propagated [9] Z.Y.Fu, H. Wang,W.M.Wang, andR.Z.Yuan, “Composites after heating the compacted powder mixture to approx- fabricated by self-propagating high-temperature synthesis,” imately 700 C, which is much lower than the synthesis Journal of Materials Processing Technology, vol. 137, no. 1–3, temperature in conventional processes. pp. 30–34, 2003. 8 Advances in Tribology [10] D. Vallauri and F. A. Deorsola, “Synthesis of TiC-TiB2- Ni cermets by thermal explosion under pressure,” Materials Research Bulletin, vol. 44, no. 7, pp. 1528–1533, 2009. [11] K. Matsuura, Y. Obara, and K. Kojima, “Combustion synthesis of boride particle dispersed hard metal from elemental powders,” International Journal of Refractory Metals and Hard Materials, vol. 27, no. 2, pp. 376–381, 2009. [12] K. Matsuura, Y. Obara, and M. Kudoh, “Fabrication of TiB2 particle dispersed FeAl-based composites by self-propagating high-temperature synthesis,” ISIJ International, vol. 46, no. 6, pp. 871–874, 2006. [13] X. Zhang and N. Liu, “Microstructure, mechanical properties and thermal shock resistance of nano-TiN modified TiC- based cermets with different binders,” International Journal of Refractory Metals and Hard Materials, vol. 26, no. 6, pp. 575– 582, 2008. [14] M. Binnewies and E. Mike, Thermochemical Data of Elements and Compounds, Wiley-VCH, 2002. [15] D. Vallauri,I.C.At´ıas Adrian, ´ and A. Chrysanthou, “TiC-TiB2 composites: a review of phase relationships, processing and properties,” Journal of the European Ceramic Society, vol. 28, no. 8, pp. 1697–1713, 2008. [16] N. Liu, W. Yin, and L. Zhu, “Effect of TiC/TiN powder size on microstructure and properties of Ti(C, N)-based cermets,” Materials Science and Engineering A, vol. 445-446, pp. 707– 716, 2007. [17] S. Cardinal, A. Malcher ` e, V. Garnier, and G. Fantozzi, “Microstructure and mechanical properties of TiC-TiN based cermets for tools application,” International Journal of Refrac- tory Metals and Hard Materials, vol. 27, no. 3, pp. 521–527, 2009. 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