Availableonlineatwww.sciencedirect.cor ° Science Direct CERAMICS INTERNATIONAL ELSEVIER Ceramics International 33(2007)1475-1480 www.elsevier.com/locate/ceramint In situ growth of TiC whiskers in Al,O3 matrix for ceramic machine tools Bingqiang Liu, Chuanzhen Huang", Xinyu Lu, Meilin Gu, Hanlian Liu Center for Advanced Jet Engineering Technologies(CaJET) School of Mechanical Engineering, Shandong University, Jinan 250061, PR China Received 5 April 2006: received in revised form 20 April 2006: accepted 25 May 2006 Available online 11 September 2006 Abstract TiC whiskers have been synthesized via a carbothermal reduction technique in an a-Al2O3 matrix within a temperature range of 1380-1580C in an argon atmosphere. The raw materials consist of TiO2, carbon, nickel and Nacl. various mixing procedures and rea lon temperatures were yield of the whiskers is mainly dependent on the mixing procedures and the morphology of the synthesized composite powders is mainly on the synthesis temperatures. The majority of the synthesized whiskers display an ideal aspect ratio of 10-30 with a diameter of 1 significant influence on the growth of the TiC whiskers by the present of the Al2O3 matrix powder can be noted Sevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: TiC whisker; a-Al2O3; Carbothermal reduction; In situ growth; Mixing procedur 1. Introduction application of TiC whiskers is limited not only by such disadvantages as discussed above, but also by high cost. In situ Moderate quantity of whiskers with high elastic modulus as growth of TiC whiskers strengthening and toughening Al2O3 n additive can greatly improve the flexural strength and matrix composite tool materials can greatly reduce the cost and fracture toughness of ceramic materials [1]. However, the environment pollution by such advantages as the direct pplication of whiskers is still limited by such disadvantages as synthesizing the whiskers in a matrix material and avoiding healthy hazard, difficult dispersion, a high cost, etc. In situ the complicated mixing procedures On the other hand, some growth of whiskers in a matrix material is a promise way to special microstructure introduced by the in situ growth overcome such disadvantages. Two patents of in situ growth procedure and some controllable byproducts or remnants such Sic whiskers strengthen Al2O3 and Si3N4 have been, as Al TiOs and carbon may lead to new composites with some respectively, reported in Japan [2]. However, SiC whiskers excellent mechanical properties. However, few reports on in have a lower thermal expansion coefficent and somewhat poor situ growth of TiC whiskers in any matrix material can be chemical stability. As a result, the pull-out effect in Al2O3/Sic currently noted whisker composites may be weakened by a thermal stress TiC whiskers can be prepare introduced by the mismatch of their thermal expansion deposition( CVD) method [4-7] or a carbothermal reduction coefficients. And cutting tools made by such composites are technology [8-ll] The CVD method is more frequently used generally used to cut Ni alloys instead of ferrous metal because to explore new whiskers. However, the carbothermal reduction of the reaction between the compound Sic and element Fe in technology is more economical and more frequently used in ferrous metal. TiC particles are commonly used as an additive large-scale commercial productions, for example, the Sic in Al2O3 matrix composite cutting tool materials [ 3] because of whiskers. Moreover, considering to obtain a composite powder the ideal physical compatibility and the chemical stability with a homogeneous distribution of whiskers in a matrix is a between the compound TiC and element Fe. However, the critical problem in such researches as in situ growth processes the carbothermal reduction technology is used in our work. TiO,. carbon and NaCl are used as the raw materials and Ni as ing author. Tel: +86 531 88392539: fax: +86 531 88392328. the catalyst. Three different mixing procedures and a synthesi temperature range of 1380-1580C are tested. The yield and 2-8842/$3200C 2006 Elsevier Ltd and Techna Group S.r.L. All rights reserved 10.1016 1-ceramint.2006.05015
In situ growth of TiC whiskers in Al2O3 matrix for ceramic machine tools Bingqiang Liu, Chuanzhen Huang *, Xinyu Lu, Meilin Gu, Hanlian Liu Center for Advanced Jet Engineering Technologies (CaJET), School of Mechanical Engineering, Shandong University, Jinan 250061, PR China Received 5 April 2006; received in revised form 20 April 2006; accepted 25 May 2006 Available online 11 September 2006 Abstract TiC whiskers have been synthesized via a carbothermal reduction technique in an a-Al2O3 matrix within a temperature range of 1380–1580 8C in an argon atmosphere. The raw materials consist of TiO2, carbon, nickel and NaCl. Various mixing procedures and reaction temperatures were used. The yield of the whiskers is mainly dependent on the mixing procedures and the morphology of the synthesized composite powders is mainly dependent on the synthesis temperatures. The majority of the synthesized whiskers display an ideal aspect ratio of 10–30 with a diameter of 1– 3 mm. No significant influence on the growth of the TiC whiskers by the present of the Al2O3 matrix powder can be noted. # 2006 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: TiC whisker; a-Al2O3; Carbothermal reduction; In situ growth; Mixing procedure 1. Introduction Moderate quantity of whiskers with high elastic modulus as an additive can greatly improve the flexural strength and fracture toughness of ceramic materials [1]. However, the application of whiskers is still limited by such disadvantages as healthy hazard, difficult dispersion, a high cost, etc. In situ growth of whiskers in a matrix material is a promise way to overcome such disadvantages. Two patents of in situ growth SiC whiskers strengthen Al2O3 and Si3N4 have been, respectively, reported in Japan [2]. However, SiC whiskers have a lower thermal expansion coefficeint and somewhat poor chemical stability. As a result, the pull-out effect in Al2O3/SiC whisker composites may be weakened by a thermal stress introduced by the mismatch of their thermal expansion coefficients. And cutting tools made by such composites are generally used to cut Ni alloys instead of ferrous metal because of the reaction between the compound SiC and element Fe in ferrous metal. TiC particles are commonly used as an additive in Al2O3 matrix composite cutting tool materials [3] because of the ideal physical compatibility and the chemical stability between the compound TiC and element Fe. However, the application of TiC whiskers is limited not only by such disadvantages as discussed above, but also by high cost. In situ growth of TiC whiskers strengthening and toughening Al2O3 matrix composite tool materials can greatly reduce the cost and environment pollution by such advantages as the direct synthesizing the whiskers in a matrix material and avoiding the complicated mixing procedures. On the other hand, some special microstructure introduced by the in situ growth procedure and some controllable byproducts or remnants such as Al2TiO5 and carbon may lead to new composites with some excellent mechanical properties. However, few reports on in situ growth of TiC whiskers in any matrix material can be currently noted. TiC whiskers can be prepared via either a chemical vapor deposition (CVD) method [4–7] or a carbothermal reduction technology [8–11]. The CVD method is more frequently used to explore new whiskers. However, the carbothermal reduction technology is more economical and more frequently used in large-scale commercial productions, for example, the SiC whiskers. Moreover, considering to obtain a composite powder with a homogeneous distribution of whiskers in a matrix is a critical problem in such researches as in situ growth processes, the carbothermal reduction technology is used in our work. TiO2, carbon and NaCl are used as the raw materials and Ni as the catalyst. Three different mixing procedures and a synthesis temperature range of 1380–1580 8C are tested. The yield and www.elsevier.com/locate/ceramint Ceramics International 33 (2007) 1475–1480 * Corresponding author. Tel.: +86 531 88392539; fax: +86 531 88392328. E-mail address: huangcz@sdu.edu.cn (C. Huang). 0272-8842/$32.00 # 2006 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2006.05.015
1476 B Liu et al. /Ceramics International 33(2007)1475-1480 morphology of the synthesized TiC whiskers in the Al2O3 successfully synthesized. Whiskers can be observed distributed matrix under different experimental conditions are studied among the Al2O3 matrix grains shown in Fig. 2. The majority of the whiskers display an ideal aspect ratio of 10-30 with 2. Experimental procedure diameter of 1-3 Fm and a smooth surface shown in Fig 3(a) No obviously agglomeration of the whiskers can be noted Commercial TiO2, amorphous carbon, Ni and chemically while some agglomeration and growth of the Al2O3 matrix pure NaCl are used as precursors. Commercial a-Al2O3 with an grains can be observed shown in Fig 3(b). Some clusters of average grain size of 0.5 um is used as the matrix material. The superfine powder with a nano-scale diameter can be observed molar ratio of T102: C: NaCl: Ni is 1: 3: 0.5: 0.05. The synthesized either among the alumina grains or adhere to the synthesize omposite powders are theoretically calculated to contain about whiskers shown in Fig. 3(a and c). Such clusters of powder are 60 vol% TiC and the actual fractions of the whiskers thought to be the carbon remnants It can be summarized that synthesized in the various experimental conditions are the yield of the whiskers is mainly dependent on the mixing compared and analyzed by the scanning electron microscope procedures and the morphology of the synthesized composite (SEM) photographs. The precursor mixtures, respectively, powders is mainly dependent on the synthesis temperature named as AT300, AT301 and AT302, are mixed by three which will be discussed below different procedures. AT300 is mixed in a blender for 30 min and sieved through a 100-mesh sieve for two times, and then 3. 2. Yield of the TiC whiskers sieved through a 200-mesh sieve for another two times. AT301 is prepared by a dry ball milling procedure for 24 h, and ther Different mixing procedures can obviously influence the sieved though a 100-mesh sieve. AT302 is dispersed for 30 min yield of the whiskers while the mechanism is still not clear [9]. by a supersonic vibration in ethanol medium and ball milled for However, to maximize the yield of the whiskers, such three 24 h, then dried in a vacuum dry box and sieved through a 100- factors combined with the mixing procedure can be summar- mesh sieve. Each 15 g of the mixed powders is, respectively, put ized as a good dispersed homogeneous mixture, improving the into a graphite reactor with several small holes on the lid to mass transport and avoiding the direct reaction between TiO allow gas exchange between the reactor and the surrounding and carbon during the synthesizing process. In the carbothermal atmosphere, heated to the synthesis temperature in 10-12 min reduction technology, the growth of the TiC whiskers is via in a flowing argon-gas atmosphere and held for 90 min duration precipitation from the Ni-C alloy droplets. The direct reaction time. The various synthesis temperatures are, respectively, between TiO2 and carbon will lead to the form of TiC particles 1380,1480and1580°C. instead of whiskers [91 The obtained phases are characterized by a power X-ray The influence of the mixing procedure on the yield of the diffractometry (XRD). The yield and morphology of the TiC whiskers are compared by the SEm photographs shown whiskers are investigated by a SEM (Hitachi S-570 SEM) ig. 2. It can be noted that the maximum yield of the TiC whiskers is obtained in AT300, which is mixed by a blender and 3. Results and discussion sieves. Such a procedure can avoid the escape of the volatile compositions in the carbon. The carbon containing a 3.1. Characterization of obtained mixture amount of volatile compositions can improve the transport in the synthesis process, and then lead to a The XRD pattern of the synthesized composite powders with yield of the TiC whiskers [9]. Lower yield is obtained in AT302 different mixing procedures and react temperatures are shown which is dis spersed for 30 min by a supersonic vibration in in Fig. 1. No TiOz can be detected by the XRD and TiC is ethanol medium and ball milled for 24 h. Such a procedure can obtain a good dispersed homogeneous mixture. However, some volatile compositions might escape during the dry process and 1。个 the high-speed ball milling procedure will enhance the active of the particles and improve their contact condition, which is somewhat similar to the mechanical alloying(MA) effect and may be named as a ball milling(BM)effect. Such an effect will be beneficial to the direct reaction of tio, and carbon The lowest yield is observed in AT301, which is mixed by a dry ball milling procedure. Volatile compositions may escape because T300 UU of the heat introduced by friction, and the BM effect will be obviously enhanced by such a mixing procedure It is found that the synthesis temperature has no obviously effect on the yield of the whiskers in AT300. However, apparently lower yield of the whiskers can be observed AT301 and AT302 synthesized at 1580C shown in Fig. 2, B0 indicating that a bm effect is working and such an effect can ig. 1. XRD of the synthesized composite powders. obviously enhanced at a higher synthesis temperature
morphology of the synthesized TiC whiskers in the Al2O3 matrix under different experimental conditions are studied. 2. Experimental procedure Commercial TiO2, amorphous carbon, Ni and chemically pure NaCl are used as precursors. Commercial a-Al2O3 with an average grain size of 0.5 mm is used as the matrix material. The molar ratio of TiO2:C:NaCl:Ni is 1:3:0.5:0.05. The synthesized composite powders are theoretically calculated to contain about 30 vol% TiC and the actual fractions of the whiskers synthesized in the various experimental conditions are compared and analyzed by the scanning electron microscope (SEM) photographs. The precursor mixtures, respectively, named as AT300, AT301 and AT302, are mixed by three different procedures. AT300 is mixed in a blender for 30 min and sieved through a 100-mesh sieve for two times, and then sieved through a 200-mesh sieve for another two times. AT301 is prepared by a dry ball milling procedure for 24 h, and then sieved though a 100-mesh sieve. AT302 is dispersed for 30 min by a supersonic vibration in ethanol medium and ball milled for 24 h, then dried in a vacuum dry box and sieved through a 100- mesh sieve. Each 15 g of the mixed powders is, respectively, put into a graphite reactor with several small holes on the lid to allow gas exchange between the reactor and the surrounding atmosphere, heated to the synthesis temperature in 10–12 min in a flowing argon-gas atmosphere and held for 90 min duration time. The various synthesis temperatures are, respectively, 1380, 1480 and 1580 8C. The obtained phases are characterized by a power X-ray diffractometry (XRD). The yield and morphology of the whiskers are investigated by a SEM (Hitachi S-570 SEM). 3. Results and discussion 3.1. Characterization of obtained mixture The XRD pattern of the synthesized composite powders with different mixing procedures and react temperatures are shown in Fig. 1. No TiO2 can be detected by the XRD and TiC is successfully synthesized. Whiskers can be observed distributed among the Al2O3 matrix grains shown in Fig. 2. The majority of the whiskers display an ideal aspect ratio of 10–30 with a diameter of 1–3 mm and a smooth surface shown in Fig. 3(a). No obviously agglomeration of the whiskers can be noted, while some agglomeration and growth of the Al2O3 matrix grains can be observed shown in Fig. 3(b). Some clusters of superfine powder with a nano-scale diameter can be observed either among the alumina grains or adhere to the synthesized whiskers shown in Fig. 3(a and c). Such clusters of powder are thought to be the carbon remnants. It can be summarized that the yield of the whiskers is mainly dependent on the mixing procedures and the morphology of the synthesized composite powders is mainly dependent on the synthesis temperatures, which will be discussed below. 3.2. Yield of the TiC whiskers Different mixing procedures can obviously influence the yield of the whiskers while the mechanism is still not clear [9]. However, to maximize the yield of the whiskers, such three factors combined with the mixing procedure can be summarized as a good dispersed homogeneous mixture, improving the mass transport and avoiding the direct reaction between TiO2 and carbon during the synthesizing process. In the carbothermal reduction technology, the growth of the TiC whiskers is via a precipitation from the Ni–C alloy droplets. The direct reaction between TiO2 and carbon will lead to the form of TiC particles instead of whiskers [9]. The influence of the mixing procedure on the yield of the TiC whiskers are compared by the SEM photographs shown in Fig. 2. It can be noted that the maximum yield of the TiC whiskers is obtained in AT300, which is mixed by a blender and sieves. Such a procedure can avoid the escape of the volatile compositions in the carbon. The carbon containing a large amount of volatile compositions can improve the mass transport in the synthesis process, and then lead to a high yield of the TiC whiskers[9]. Lower yield is obtained in AT302, which is dispersed for 30 min by a supersonic vibration in ethanol medium and ball milled for 24 h. Such a procedure can obtain a good dispersed homogeneous mixture. However, some volatile compositions might escape during the dry process and the high-speed ball milling procedure will enhance the active of the particles and improve their contact condition, which is somewhat similar to the mechanical alloying (MA) effect and may be named as a ball milling (BM) effect. Such an effect will be beneficial to the direct reaction of TiO2 and carbon. The lowest yield is observed in AT301, which is mixed by a dry ball milling procedure. Volatile compositions may escape because of the heat introduced by friction, and the BM effect will be obviously enhanced by such a mixing procedure. It is found that the synthesis temperature has no obviously effect on the yield of the whiskers in AT300. However, apparently lower yield of the whiskers can be observed in AT301 and AT302 synthesized at 1580 8C shown in Fig. 2, indicating that a BM effect is working and such an effect can be obviously enhanced at a higher synthesis temperature. 1476 B. Liu et al. / Ceramics International 33 (2007) 1475–1480 Fig. 1. XRD of the synthesized composite powders
B Liu et al./Ceramics Intemational 33(2007)1475-1480 477 AT300 AT301 1380℃ 1380℃ 85991115Ky氵’ bg5001115kyi的到u靠 AT302 AT30 1380℃ 1480℃ 95991115KV 30um (c) 95891115KV AT301 AT302 1480℃ 80℃ 8581115KV Fig. 2.(a-i)Yield of whiskers at different experimental conditions
B. Liu et al. / Ceramics International 33 (2007) 1475–1480 1477 Fig. 2. (a–i) Yield of whiskers at different experimental conditions
1478 B Liu et al. /Ceramics International 33(2007)1475-1480 AT30 1580℃ 95881115Ky氵i:函∵u 85981115K氵i; AT302 1580℃ 85981115KV氵i:∵3u静 2.(Continued) 3.3. Morphology of the mixture synthesis temperature is elevated to 1580C. Severe matrix The morphology of the mixture is mainly dependent on the grain agglomeration can be observed in AT300 shown in Fig. 2, synthesis temperature. Some whiskers with a square cross- indicating a poor dispersion of the raw mixture section and a rough axial surface can be observed in the composite powders synthesized at 1380C shown in Fig 3(c), 3.4. The influence of the matrix Al2O3 powder whereas only round and smooth whiskers can be found at a higher synthesis temperature such as 1480 and 1580C Such Before the experimental in situ growth of the TiC results as the influence on the yield of the whiskers by the whiskers, it has been observed by the experiments of in situ mixing procedures and the influence on their morphology by growth of TiC Ni-x whiskers in Al2O3 matrix that a the synthesis temperatures are consistent with the details carbothermal reduction process of the Al2O3 can also take discussed by Ahlen et al. [8, 9], indicating that there is no place. AlO is detected at 1250C and aiN is at 1550C on significant influence on the growth of the whiskers by the the XRD pattern. However, there is no other compounds present of the alumina matrix powder. except Due to the present of Al2O3 powder, no obviously some Ni-C alloy can be noted on the Xrd patterns of in agglomeration of the whiskers can be noted. However, situ growth of TiC whiskers, indicating that a-Al2O3 is stable agglomeration and growth of the matrix grains can be observed in the argon-gas atmosphere at the synthesis temperatures shown in Fig. 3(b). Obviously growth of the matrix grains can and will not participate in the carbothermal reduction be observed in the products synthesized at 1480C. Some of process
3.3. Morphology of the mixture The morphology of the mixture is mainly dependent on the synthesis temperature. Some whiskers with a square crosssection and a rough axial surface can be observed in the composite powders synthesized at 1380 8C shown in Fig. 3(c), whereas only round and smooth whiskers can be found at a higher synthesis temperature such as 1480 and 1580 8C. Such results as the influence on the yield of the whiskers by the mixing procedures and the influence on their morphology by the synthesis temperatures are consistent with the details discussed by Ahlen et al. [8,9], indicating that there is no significant influence on the growth of the whiskers by the present of the alumina matrix powder. Due to the present of Al2O3 powder, no obviously agglomeration of the whiskers can be noted. However, agglomeration and growth of the matrix grains can be observed shown in Fig. 3(b). Obviously growth of the matrix grains can be observed in the products synthesized at 1480 8C. Some of them can grow from the origin 0.5 to 3–4 mm when the synthesis temperature is elevated to 1580 8C. Severe matrix grain agglomeration can be observed in AT300 shown in Fig. 2, indicating a poor dispersion of the raw mixture. 3.4. The influence of the matrix Al2O3 powder Before the experimental in situ growth of the TiC whiskers, it has been observed by the experiments of in situ growth of TiCxN1x whiskers in Al2O3 matrix that a carbothermal reduction process of the Al2O3 can also take place. AlO is detected at 1250 8C and AlN is at 1550 8C on the XRD pattern. However, there is no other compounds except for the synthesized TiC, the alumina matrix and some Ni–C alloy can be noted on the XRD patterns of in situ growth of TiC whiskers, indicating that a-Al2O3 is stable in the argon-gas atmosphere at the synthesis temperatures and will not participate in the carbothermal reduction process. 1478 B. Liu et al. / Ceramics International 33 (2007) 1475–1480 Fig. 2. (Continued).
B. Liu et al/Ceramics Intemational 33(2007)1475-1480 479 AT302 AT302 1480℃ 1580℃ 51115KM4,8K 85981115K氵4:忘m AT302 1380℃ 5981115K氵4:与m (c Fig 3. (a-c)Morphology of the whiskers and grains. 35. The carbon remnants photographs shown in Fig 3(a and c). It has been reported [3] that the fracture toughness of Al2O3/TiC ceramic material can TiC is a non-stoichiometric compound where the atomic be increased by a moderately added amount of carbon fraction of C can change from 0.32 to O.5. The compound TiC However, such clusters of the carbon remnants as shown in with a high atomic fraction of C such as 0.5 is difficult to be Fig. 3(c)will certainly decrease the dense and mechanical synthesized, and then the carbon remnants can hardly be properties of the sintered composite. So the amount of the avoided when a stoichiometric amount of carbon has been carbon remnants in the synthesized composite powder must used in our work. However, the carbon used in the work is be controlled To decrease the added amount of carbon may be with an amorphous phase, which is difficult to be detected by one of the methods to avoid the excessive carbon remnants the Xrd patterns whereas can be observed by the SEM However, such a method may also decrease the atomic
3.5. The carbon remnants TiC is a non-stoichiometric compound where the atomic fraction of C can change from 0.32 to 0.5. The compound TiC with a high atomic fraction of C such as 0.5 is difficult to be synthesized, and then the carbon remnants can hardly be avoided when a stoichiometric amount of carbon has been used in our work. However, the carbon used in the work is with an amorphous phase, which is difficult to be detected by the XRD patterns whereas can be observed by the SEM photographs shown in Fig. 3(a and c). It has been reported [3] that the fracture toughness of Al2O3/TiC ceramic material can be increased by a moderately added amount of carbon. However, such clusters of the carbon remnants as shown in Fig. 3(c) will certainly decrease the dense and mechanical properties of the sintered composite. So the amount of the carbon remnants in the synthesized composite powder must be controlled. To decrease the added amount of carbon may be one of the methods to avoid the excessive carbon remnants. However, such a method may also decrease the atomic B. Liu et al. / Ceramics International 33 (2007) 1475–1480 1479 Fig. 3. (a–c) Morphology of the whiskers and grains.
1480 B Liu et al. /Ceramics International 33(2007)1475-1480 fraction of C in the TiC whiskers. It seems from our Special Foundation for University Doctor Discipline of experimental results that the amount of carbon remnants can Ministry of Education(20030422012), China. be decreased when the synthesis temperature is elevated However, growth and agglomeration of the matrix grains can References also become severe [1] C.Z. Huang, X. Ai, Development of advanced composite ceramic tool 4. Conclusions material, Mater Res. Bull. 31(1996)951-956 [2 Y.Q. Wu, Y.F. Zhang, J K Guo, In situ growth whiskers reinforced The TiC whiskers have been successfully synthesized in an [3] C.H. Xu, C.Z. Huang, Z Q. Li, X Ai, Toughening mechanisms of Al2O3 matrix. The majority of the whiskers have an ideal aspect TiC ceramic composite with carbon additive, J Inorg. Mater. 16 ratio of 10-30 with a diameter of 1-3 um. The yield of the 256-262. whiskers is mainly dependent on the mixing procedures and the 42. Wokulski, K. Wokulski, On the growth and morphology of TiC, hikers, J. Cryst. Growth 62(1983)439-446. of the mixtures is mainly depende the [5] Z. Wokulski, The influence of nickel on VLS growth and real structure of ynthesis temperatures. The maximum yield of the whiskers TiC whiskers, J Cryst. Growth 82(1987)427-434. can be obtained in a raw material mixed by a blender and sieves [6] NTamari, A Kato, Catalytic effect of various metal and refractory oxides and smoothly round whiskers can be obtained at a highe on the growth of TiC whiskers by chemical vapor deposition, J. Cryst. synthesis temperature of 1480 and 1580C Growth46(1979)221-237 I Y.w. Yuan, J.S. Pan, The effect of vapor phase on the growth of TiC No significant influence of the present of a-Al2O3 matrix whiskers prepared by chemical vapor deposition, J. Cryst. Growth 193 wder on the growth of the TiC whiskers can be noted. Thus, (1998)585-591 the a-Al2O3 is stable at the synthesis temperatures when the []N Ahlen, M Johnsson, A.K. Larsson, B Sundman, On the carbothermal whiskers are grown in an argon-gas atmosphere. Clusters of apor-liquid-solid (vls)mechanism for TaC, TiC, and Ta Til-AC whisker carbon remnants can be observed on the SEM photographs, the growth, J. Eur. Ceram. Soc. 20(2000)2607-2618. [9] N. Ahlen, M. Johnsson, M. Nygren, Carbothermal synthesis of tic amount of which should be controlled whiskers via a vapor-liquid-solid growth mechanism, J. Am. Ceram. c.79(1996)2803-2808. Acknowledgements [10] M. Johnsson, Synthesis of boride, carbide, and carbonitride whiskers, Solid State ionics 172(2004)365-368. 11]RV. Krishnarao, J Subrahmanyam, V. Ramakrishna, Synthesis of TiC This project was supported by Excellent Young Teacher hikers through carbothermal reduction of TiO2, J. Mater. Synth. upport Program of Ministry of Education(No. 2003-79)and Process.9(2001)1-10
fraction of C in the TiC whiskers. It seems from our experimental results that the amount of carbon remnants can be decreased when the synthesis temperature is elevated. However, growth and agglomeration of the matrix grains can also become severe. 4. Conclusions The TiC whiskers have been successfully synthesized in an Al2O3 matrix. The majority of the whiskers have an ideal aspect ratio of 10–30 with a diameter of 1–3 mm. The yield of the whiskers is mainly dependent on the mixing procedures and the morphology of the mixtures is mainly dependent on the synthesis temperatures. The maximum yield of the whiskers can be obtained in a raw material mixed by a blender and sieves and smoothly round whiskers can be obtained at a higher synthesis temperature of 1480 and 1580 8C. No significant influence of the present of a-Al2O3 matrix powder on the growth of the TiC whiskers can be noted. Thus, the a-Al2O3 is stable at the synthesis temperatures when the whiskers are grown in an argon-gas atmosphere. Clusters of carbon remnants can be observed on the SEM photographs, the amount of which should be controlled. Acknowledgements This project was supported by Excellent Young Teacher Support Program of Ministry of Education (No. 2003-79) and Special Foundation for University Doctor Discipline of Ministry of Education (20030422012), China. References [1] C.Z. Huang, X. Ai, Development of advanced composite ceramic tool material, Mater. Res. Bull. 31 (1996) 951–956. [2] Y.Q. Wu, Y.F. Zhang, J.K. Guo, In situ growth whiskers reinforced ceramic composites, Mater. Rev. 14 (2000) 20–22. [3] C.H. Xu, C.Z. Huang, Z.Q. Li, X. Ai, Toughening mechanisms of Al2O3/ TiC ceramic composite with carbon additive, J. Inorg. Mater. 16 (2001) 256–262. [4] Z. Wokulski, K. Wokulski, On the growth and morphology of TiCx whiskers, J. Cryst. Growth 62 (1983) 439–446. [5] Z. Wokulski, The influence of nickel on VLS growth and real structure of TiC whiskers, J. Cryst. Growth 82 (1987) 427–434. [6] N. Tamari, A. Kato, Catalytic effect of various metal and refractory oxides on the growth of TiC whiskers by chemical vapor deposition, J. Cryst. Growth 46 (1979) 221–237. [7] Y.W. Yuan, J.S. Pan, The effect of vapor phase on the growth of TiC whiskers prepared by chemical vapor deposition, J. Cryst. Growth 193 (1998) 585–591. [8] N. Ahlen, M. Johnsson, A.-K. Larsson, B. Sundman, On the carbothermal vapor–liquid–solid (vls) mechanism for TaC, TiC, and TaxTi1xC whisker growth, J. Eur. Ceram. Soc. 20 (2000) 2607–2618. [9] N. Ahlen, M. Johnsson, M. Nygren, Carbothermal synthesis of tic whiskers via a vapor–liquid–solid growth mechanism, J. Am. Ceram. Soc. 79 (1996) 2803–2808. [10] M. Johnsson, Synthesis of boride, carbide, and carbonitride whiskers, Solid State Ionics 172 (2004) 365–368. [11] R.V. Krishnarao, J. Subrahmanyam, V. Ramakrishna, Synthesis of TiC whiskers through carbothermal reduction of TiO2, J. Mater. Synth. Process. 9 (2001) 1–10. 1480 B. Liu et al. / Ceramics International 33 (2007) 1475–1480