Goto  Takashi

Li  Wenjun

Tu  Rong

MATERIALS TRANSACTIONS

Li, Wenjun

Tu, Rong

Goto, Takashi

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Preparation of TiC-TiB2-SiC ternary eutectic composites by arc-melting and their characterizations

Tohoku University Repository (TOUR) / 東北大学機関リポジトリ

Preparation of TiC-TiB2-SiC ternary eutecticcomposites by arc-melting and theircharacterizations著者 Li  Wenjun, Tu  Rong, Goto  Takashijournal orpublication titleMaterials Transactionsvolume 47number 4page range 1193-1197year 2006URL http://hdl.handle.net/10097/52285Preparation of TiC-TiB2-SiC Ternary Eutectic Compositesby Arc-Melting and Their CharacterizationsWen-Jun Li, Rong Tu and Takashi GotoInstitute for Materials Research, Tohoku University, Sendai 980-8577, JapanTiC-TiB2-SiC composites were synthesized by arc-melting using TiC, TiB2 and SiC powders as starting materials in Ar atmosphere. TiC-TiB2-SiC system was a ternary eutectic, whose eutectic composition was 34TiC-22TiB2-44SiC (mol%). The TiC-TiB2-SiC eutectic compositeshowed a lamellar texture, where lamellar SiC grains paralleled to lamellar TiC grains. TiB2 grains had an angle of about 30 to 60 with lamellarSiC and TiC grains. The hardness of TiC-TiB2-SiC eutectic composite was 25.5GPa at the load of 1.96N and increased with increasing TiCcontent. The electrical conductivity of the eutectic composite was 2:81 103 Sm1 at the room temperature and decreased with increasingtemperature. The thermal conductivity of the eutectic composite was 25 to 60WK1 m1 at the room temperature and decreased with increasingtemperature. The electrical conductivity of TiC-TiB2-SiC ternary composites decreased with increasing SiC content, and the thermalconductivity decreased with increasing TiC content.(Received September 26, 2005; Accepted February 13, 2006; Published April 15, 2006)Keywords: TiC-TiB2-SiC, phase diagram, eutectic composite, arc-melted method1. IntroductionSilicon carbide shows high hardness, excellent oxidationresistance, good thermal shock resistance and high-temper-ature strength.1–3) Titanium boride (TiB2) has high hardness,high wear resistance, high thermal conductivity and highelectrical conductivity.4–7) Titanium carbide is an engineer-ing material with five independent slip systems allowing thematerial to be ductile above 1000K. That is also an usefulcharacteristic as an additive material to improve the perform-ance of SiC and/or TiB2-based composites.8–15) Therefore,TiC-TiB2-SiC system composites could be an excellentmaterial due to several combined properties of SiC, TiC andTiB2 such as high hardness and high thermal conductivity.TiC-TiB2-SiC composites has been synthesized by hot-pressing and reactive hot-pressing. Mestral et al.16) reportedthe preparation of TiC-TiB2-SiC composites with the relativedensity of 99.8% by hot-pressing at 2473K. The fracturestrength of the TiC-TiB2-SiC composites obtained was1070MPa, and the fracture toughness was 6.7MPam1=2.Zhang et al.17) prepared TiC-TiB2-SiC composites with therelative density of 99.8% by reactive hot-pressing usingTiH2, Si and B4C as starting materials at 2273K. The fracturestrength of the TiC-TiB2-SiC composites was 680MPa, andthe fracture toughness was 6.9MPam1=2.On the other hand, the self-assembly of microstructureduring the solidification of melted ceramic materials can be auseful technique to develop high-performance compositematerial. Particularly, an eutectic texture may improve theproperties of ceramic composites. Some promising resultshave been reported for the B4C-SiC, B4C-TiB2 and B4C-TiB2-SiC eutectic composites.18–20) However, the study onthe TiC-TiB2-SiC eutectic composite has not been reported.In this study, the TiC-TiB2-SiC ternary composites wereprepared by arc-melting, and the microstructure, hardness,thermal conductivity and electrical conductivity were inves-tigated.2. Experimental ProcedureTiC, TiB2 and SiC powders were used as startingmaterials. The powders were weighed and mixed in an agatemortar by adding a small amount of ethanol. The content ofTiC and TiB2 was changed from 0 to 80mol% and that of SiCwas changed from 0 to 70mol%. The mixtures of powderswere then pressed into disks with 10mm in diameter and5mm in thickness at 30MPa. The specimens were meltedand solidified on water-cooled copper holder for two times byarc-melting in Ar atmosphere of about 60 kPa. Each meltingtime was fixed at 30 s.The crystal phase of composites was investigated by X-raydiffraction (XRD). The microstructure was observed byscanning electron microscopy (SEM). The hardness wasmeasured by a hardness tester (MVK-E) and calculated fromthe average value of 30 points indented at random. Thefracture toughness was calculated from eq. (1):21)KIc ¼ 0:0719ðP=C3=2Þ ð1Þwhere P is the indentation load (N) and C the half of averagecracks length (m). The electrical conductivity was measuredby a DC four-probed method for rectangular specimens. Thethermal conductivity was measured by a laser flash methodusing disk specimens in the temperature range between theroom temperature and 1023K.3. Results and Discussion3.1 Microstructure of TiC-TiB2-SiC compositesFigure 1 shows the XRD pattern of composites prepared atthe composition of (a) 34TiC-22TiB2-44SiC, (b) 10TiC-30TiB2-60SiC, (c) 70TiC-10TiB2-20SiC and (d) 30TiC-40TiB2-30SiC (mol%). The phases of the composites wereTiC, TiB2 and SiC, and no other phase appeared. The relativeXRD intensities of TiC, TiB2 and SiC peaks depended on thecontent of TiC, TiB2 and SiC in the composites. Figure 2shows several typical microstructures of TiC-TiB2-SiCcomposites for the cross-section perpendicular to the growthMaterials Transactions, Vol. 47, No. 4 (2006) pp. 1193 to 1197#2006 The Japan Institute of Metalsdirection, where the white phase is TiC, the gray phase isTiB2 and the black phase is SiC. The microstructure of 9TiC-26TiB2-65SiC (mol%) composite was the rod SiC grains co-existing with binary and ternary eutectic textures as shown inFig. 2(a). TiB2-SiC binary eutectic and TiC-TiB2-SiC ter-nary eutectic textures were observed at the composition of10TiC-30TiB2-60SiC (mol%) as shown in Fig. 2(b). TheTiB2-SiC binary eutectic texture (BE1) was surrounded bythe TiC-TiB2-SiC ternary eutectic texture (TE), suggestingthat the TiB2-SiC binary eutectic phase first precipitated andthen TiC-TiB2-SiC ternary eutectic solidified correspondingto the ternary eutectic phase diagram. Figure 3 demonstratesthe TiC-TiB2-SiC ternary phase diagram. The composition of10TiC-30TiB2-60SiC (mol%) was on the binary eutecticcurve line, as indicated by a dash line in Fig. 3. The ternaryeutectic point can be assumed from the microstructureobservation. However, the ternary eutectic point could beindistinguishable due to the similar binary and ternaryeutectic textures. We have reported that the ternary eutecticpoint of B4C-TiB2-SiC system can be determined from themicrostructures observation for the compositions betweenternary eutectic texture and the each end component asmarked by dotted lines in Fig. 3. The microstructure at thecomposition of 70TiC-10TiB2-20SiC and 30TiC-40TiB2-30SiC (mol%) were spherical TiC grains and elongated rodTiB2 grains co-existing with the eutectic texture, respective-ly, as shown in Figs. 2(c) and 2(d). These composition pointswere on the lines between the ternary eutectic point and TiB2or TiC, respectively. The TiC-TiB2-SiC ternary eutecticcomposition was determined as 34TiC-22TiB2-44SiC(mol%), where no primary phases were observed. A fewresearchers reported the solid state sintering of the TiC-TiB2-SiC composites by hot-pressing and measured their mechan-ical properties.16,17) However, no study on the ternary eutecticcomposite by melt-solidification was reported. The ternaryeutectic point was abbreviated as TE, and the binary eutecticpoints were abbreviated as BE1 for 40TiB2-60SiC (mol%)22)and BE2 for 28TiB2-72TiC (mol%).23) In the TiB2 primaryphase area, the microstructure can be mainly categorized intoTiB2+TE+BE1, TiB2+TE and TiB2+TE+TiC. AlthoughTiB2, BE2 and TE might have been expected near thecomposition of BE2, no BE2 was identified. However, in ourexperiments on the TiC-TiB2 binary system, the typicallamellar texture of TiC-TiB2 eutectic was observed.23) Thecompositions of high content SiC were easily evaporated dueto decomposition of SiC. The TiC-SiC binary system mightbe also an eutectic system and the details will be reportedelsewhere. Figure 4 shows that the SEM photographs of theTiC-TiB2-SiC eutectic composite for the cross-sectionperpendicular (a) and parallel (b) to the growth direction.The white, gray and black phases were TiC, TiB2, and SiCgrains, respectively. TiC, SiC and TiB2 grains showedlamellar texture of 3, 3 and 2 mm in thickness, respectively.10 20 30 40 50 60 70 80(d)(c)(b)(a)SiC (222)SiC (311)SiC (220)TiB2 (201)TiB2 (200)TiB2 (102)TiB2 (110)TiB2 (002)TiB2 (001)TiB2 (100)TiC (200)TiC (222)TiC (311)TiC (220)TiC (111)SiC (111)SiC (200)TiB2 (101)TiB2 (201)TiC (222)SiC (222)TiC (311)TiB2 (200)SiC (311)TiB2 (102)TiB2 (110)TiC (220)SiC (220)TiB2 (002)TiB2 (101)TiC (200)SiC (200)TiC (111)SiC (111)TiB2 (100)TiB2 (001)Intensity (a.u.)2θ (CuKα)Fig. 1 XRD pattern of composites with the composition of (a) 34TiC-22TiB2-44SiC, (b) 10TiC-30TiB2-60SiC, (c) 70TiC-10TiB2-20SiC and(d) 30TiC-40TiB2-30SiC (mol%).SiCTEBE1TiB2TiC10 µm(a)(c) (d)(b)2 µm 2.5 µm10 µmFig. 2 SEM photograph of composites with composition of (a) 9TiC-26TiB2-65SiC, (b) 10TiC-30TiB2-60SiC (mol%), (c) 70TiC-10TiB2-20SiC, (d) 30TiC-40TiB2-30SiC.SiCTiCTiB2 TiC + SiC + TETiB2 + TETiB2 + TiC + TE Binary eutectic (BE2)TiB2 + BE1SiC + BE1TiC + TETernary eutectic  (TE)Binary eutectic (BE1)TE + BE1Fig. 3 phase diagram of TiC-TiB2-SiC composites.1194 W.-J. Li, R. Tu and T. GotoLamellar SiC grains paralleled to lamellar TiC grains. TiB2layers had an angle of about 30 or 60 with lamellar SiC andTiC grains, which tilted the angle of 5 to 10 to the growthdirection (Fig. 4(b)). Figure 5 shows XRD patterns of theTiC-TiB2-SiC eutectic composite for the cross-sectionperpendicular to the growth direction compared with thepowder XRD pattern. The intensities of TiC(111), TiB2(100),and SiC(111) peaks in the ternary eutectic composite werestrongest (Fig. 5(a)), whereas the strongest peaks of powdersamples were TiC(200), TiB2(101) and SiC(200) as shown inFig. 5(b), respectively. Therefore, the growth direction of theternary eutectic composite was almost perpendicular toTiC(111), TiB2(100), and SiC(111).3.2 Characterization of TiC-TiB2-SiC compositesFigure 6 shows the indenter load dependence of Vickersmicro hardness of the TiC-TiB2-SiC composites at thecomposition of 10TiC-30TiB2-60SiC, 34TiC-22TiB2-44SiC,30TiC-40TiB2-30SiC and 70TiC-10TiB2-20SiC (mol%),respectively. The hardness of TiC-TiB2-SiC compositeincreased with decreasing indenter load. The hardness ofthe TiC-TiB2-SiC eutectic composite was about 25GPa at theload of 1.96N, which was close to that of composites sinteredby hot-pressing at 2373K.3) Figure 7 shows the indention ofthe TiC-TiB2-SiC composites at the load of 4.9N at thecomposition of (a) 10TiC-30TiB2-60SiC, (b) 34TiC-22TiB2-44SiC, and (c) 30TiC-40TiB2-30SiC (mol%). The fracturetoughness was calculated as 3, 5 and 4MPam1=2 at thecomposition of 10TiC-30TiB2-60SiC, 34TiC-22TiB2-44SiC,and 30TiC-40TiB2-30SiC (mol%), respectively. This resultindicates that the eutectic composite has a higher fracturestrength. Zhang et al. and Mestral et al. reported that thefracture toughness of TiC-TiB2-SiC composites was 4 to 7depending on the composition, and plotted calculatedisofracture toughness curves in the ternary system using asecond order polynomial model.16,17) From the contour curve,the fracture toughness of 10TiC-30TiB2-60SiC, 34TiC-22TiB2-44SiC (TE), and 30TiC-40TiB2-30SiC (mol%) couldbe estimated as 5.5, 6.4 and 6.1, respectively. Although ourexperimental values were slightly lower than the calculatedvalues, the trend was in agreement to the calculation.Figure 8 shows the temperature dependence of electricalconductivity of the TiC-TiB2-SiC composites at the compo-sition of 70TiC-10TiB2-20SiC, 30TiC-40TiB2-30SiC,34TiC-22TiB2-44SiC and 10TiC-30TiB2-60SiC (mol%),respectively. The electrical conductivity of TiC-TiB2-SiCcomposites decreased with increasing temperature and SiCcontent. The electrical conductivity of the TiC-TiB2-SiCeutectic composite was 2:81 103 Sm1 at the room temper-ature. The electrical conductivity of the TiC-TiB2-SiCeutectic composite was compared with those simulated by(a) (b)5 µm 5 µmGrowth directionFig. 4 SEM photograph of TiC-TiB2-SiC eutectic composites for cross-section perpendicular (a) and parallel (b) to the growth direction.10 20 30 40 50 60 70 80TiB2 (200)TiC (111)SiC (111)TiB2 (100)TiB2 (201)TiC (222)SiC (222)TiC (311)TiB2 (200)SiC (311)TiB2 (102)TiB2 (110)TiC (220)SiC (220)TiB2 (002)TiB2 (101)TiC (200)SiC (200)TiC (111)SiC (111)TiB2 (100)TiB2 (001)(b)(a)Intensity (a.u.)2θ (CuKα)Fig. 5 XRD pattern of TiC-TiB2-SiC eutectic composite for (a) cross-section perpendicular to the growth direction comparing with (b) itspowder XRD pattern.0 2 4 6 8 10202224262830Vickers micro hardness, Hv / GPaLoad, P / N10TiC-30TiB2-60SiC (mol%)34TiC-22TiB2-44SiC70TiC-10TiB2-20SiC 30TiC-40TiB2-30SiC Fig. 6 Indenter load dependence of Vickers micro hardness of TiC-TiB2-SiC composites.Preparation of TiC-TiB2-SiC Ternary Eutectic Composites by Arc-Melting and Their Characterizations 1195parallel, series and effective medium approximation models(EMA) expressed as eqs. (2), (3) and (4), respectively.24)cal (parallel) ¼ VAA þ VBB þ VCC ð2Þcal (series)1 ¼ VAA1 þ VBB1 þ VCC1 ð3Þcal(EMA)  A2cal(EMA) þ AVA þcal(EMA)  B2cal(EMA) þ BVBþcal(EMA)  C2cal(EMA) þ CVC ¼ 0 ð4Þwhere  is the electrical conductivity, V is a volume fraction,and subscripts (A, B and C) indicate the component of thecomposite. The experimental values for eutectic composite(closed square) were inbetween cal (parallel) and cal (seris). Thisresult is consistent with the eutectic microstructure observa-tion by SEM. Figure 9 shows the temperature dependence ofthermal conductivity of TiC-TiB2-SiC composites at thecomposition of 70TiC-10TiB2-20SiC, 10TiC-30TiB2-60SiC,34TiC-22TiB2-44SiC and 30TiC-40TiB2-30SiC (mol%).The thermal conductivity of TiC-TiB2-SiC composite de-creased with increasing temperature, and decreased withincreasing TiC content. The thermal conductivity of theeutectic composite was about 56WK1 m1 at the roomtemperature. The thermal conductivity was also comparedwith those simulated by the parallel, series and EMA modelsas expressed in eqs. (2) to (4),24) where  should besubstituted by thermal conductivity (). The experimentalvalues were closer to the cal (EMA) than cal (series) andcal (parallel). The phonon scattering at the phase boundariesmight affect the decrease of  values. The impurity in the SiCphase such as Ti and B could also reduce the  value of theeutectic composite. The reference  value of SiC might bealso slightly too large for the calculation of  values. Underthese consideration, both experimental  and  values werewell explained by the same model.4. ConclusionsTiC-TiB2-SiC was a ternary eutectic system. The eutecticcomposition was 34TiC-22TiB2-44SiC (mol%), and had atypical lamellar texture. TiC (111), SiC (111) and TiB2 (100)5 µm(b)5 µm(a) (c)5 µmFig. 7 Indention of Vickers micro hardness of the TiC-TiB2-SiC composites in 4.9N loading at the composition of (a) 10TiC-30TiB2-60SiC, (b) 34TiC-22TiB2-44SiC, (c) 30TiC-40TiB2-30SiC (mol%).1.0 1.5 2.0 2.5 3.0 3.52345678log ( Electrical conductivity, σ / Sm-1 )1000 500 300Temperature, T / K10-1T -1 / 10-3 K-12SiCTiBσcal(parallel)σcal(EMA)σcal(series)TiC10TiC-30TiB2-60SiC (mol%)34TiC-22TiB2-44SiC70TiC-10TiB2-20SiC 30TiC-40TiB2-30SiC Fig. 8 Temperature dependence of electrical conductivity of TiC-TiB2-SiC composites.200 400 600 800 100020406080Thermal conductivity, κ / WK-1m-1Temperature, T / K10TiC-30TiB2-60SiC (mol%)34TiC-22TiB2-44SiC70TiC-10TiB2-20SiC 30TiC-40TiB2-30SiC 100SiCTiB21200κcal(series)κcal(EMA)κcal(parallel)TiCFig. 9 Temperature dependence of thermal conductivity of TiC-TiB2-SiCcomposites.1196 W.-J. Li, R. Tu and T. Gotoof the eutectic composite were perpendicular to the growthdirection. The hardness of TiC-TiB2-SiC composites increas-ed with increasing TiC content. The hardness of the eutecticcomposite was 25.5GPa. The electrical conductivity decreas-ed with increasing SiC content. The electrical conductivity ofthe eutectic composite was 2:81 103 Sm1 at the roomtemperature. The thermal conductivity decreased with in-creasing TiC content. The thermal conductivity of theeutectic composite was about 25 to 60WK1 m1.REFERENCES1) P. T. B. Shaffer: Mater. Res. Bul. 4 (1969) 213–219.2) S. K. Lee, W. Ishida and S. Y. Lee: J. Euro. Ceram. Soc. 25 (2005) 569–576.3) D. R. Serist: J. Am. Ceram. Soc. 47 (1964) 127–130.4) K. Koumoto: Am. Ceram. Soc. Bull. 73 (1994) 84–87.5) A. D. McLeod, J. S. Haggerty and D. R. Sadoway: J. Am. Ceram. Soc.67 (1984) 705–508.6) W. M. Wang, Z. Y. Fu and H. Wang: J. Euro. Ceram. Soc. 22 (2002)1045–1049.7) Y. S. Kwon, J. S. Kim and J. J. Park: Mater. Sci. Forum 449 (2004)1113–1116.8) F. Li, L. L. Regel and W. R. Wilcox: J. Crys. 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Preparation of TiC-TiB2-SiC ternary eutectic composites by arc-melting and their characterizations

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