CERAMICS INTERNATIONAL ELSEVIER Ceramics International 33(2007)385-388 www.elsevier.com/locate/ceramint Improvement of mechanical properties of Al2O3/Ti3 SiC2 multilayer ceramics by adding Sic whiskers into alo la 3 ayers Zan Qingfeng. D, Dong Limin, Wang Chena Institute of Nuclear and New Energy Technology Tsinghua University, Beijing 100084, PR China b State Key Laboratory of New Ceramics and Fine Processing, Department of Materials Science and Engineering Tsinghua University, Beijing 100084, PR China Received 3 August 2005: received in revised form 18 August 2005: accepted 4 October 2005 Available online 28 February 2006 Abstract Al2O, /Ti3 SiC2 multilayer materials with high mechanical properties in terms of bending strength and work of fracture have been prepared by in situ hot-pressing at 1600C for 4 h In order to further improving the mechanical properties, SiC whiskers were added to Al2O3 layers as the 2nd level toughening agent with the content of Sic whisker increasing the bending strength and work of fracture showed a similar trend of increasing firstly and then decreasing. Hence, the optimal mechanical properties of 688 MPa for bending strength and 2583 J/m2 for work of fracture were btained when the added content of Sic whisker was 20 wt%. These excellent properties should be attributed to 1st-level toughening mechanism multilayer structural toughening ), 2nd-level toughening mechanism(whisker toughening), and the synergy effect between them. Hence, adding Sic whiskers was an effective approach to improving the mechanical properties C 2005 Elsevier Ltd and Techna Group S.r.L. All rights reserved. Keywords: B. Whisker; D Al2O3; Ti3SiC2; Toughening mechanism; Multilayer ceramics 1. Introduction Si3N,/BN [10, 11], SiC/C [9, 12, Al,, [13], etc. and several 10-folds of fracture toughness and several 100-folds of Ceramics are brittle and sometimes they fail catastrophically. work of fracture were achieved compared to the monolithic This limits theirapplications in engineering. In to overcome ceramics. Al2O3/Ti3SiC2 multilayer ceramics is a typical the problem, studying of toughening becomes a very important multilayer material, which possess good mechanical properties research area in ceramics, especially structural ceramics. As a of 659 MPa for bending strength and 2159 J/m- for work of result, many toughening methods had been devised, researched fracture [14] and used in ceramics, such as whisker toughening[ 1-3, long-and In recent years, synergy mechanism between two or more short-fiber toughening [4,5], dispersed rigid particle toughening toughening methods was reported [15]. By this toughening [61, ZrO2 phase transformation toughening [7, 8], andso on. These mechanism, the toughness effect was usually larger than the toughening methods were all effective for some ceramics, additional effect brought by the individual toughening hereinto whiskers were used very widely mechanisms. The all fore-mentioned toughening mechanisms Otherwise, multilayer structural toughening was proved as could be used in synergy toughening design of ceramics by an effective toughening mechanism [9-12]. Since the SiC/c appropriate methods. multilayer ceramics was first developed by Clegg et al. [9], this In this paper, the SiC whiskers as 2nd-level toughening agent toughening approach has been used in many systems, such as were added into Al2O3 layers in Al2O3/Ti3 SiC2 multilayer ceramics. The 2nd-level toughening mechanism in the multi layer ceramics, the synergy effect between the multilevel Corresponding author. Tel. +86 10 897961 12: fax: +86 10 89796118 toughening mechanisms and the fractural behavior of the whole materials will be described in this paper. 2-8842/$32.00 2005 Elsevier Ltd and Techna Group S.r.L. All rights reserved 10.1016 1. ceramist.2005.10.007
Improvement of mechanical properties of Al2O3/Ti3SiC2 multilayer ceramics by adding SiC whiskers into Al2O3 layers Zan Qingfeng a,b, *, Dong Limin a , Wang Chen a , Wang Chang-an b , Huang Yong b a Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, PR China b State Key Laboratory of New Ceramics and Fine Processing, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, PR China Received 3 August 2005; received in revised form 18 August 2005; accepted 4 October 2005 Available online 28 February 2006 Abstract Al2O3/Ti3SiC2 multilayer materials with high mechanical properties in terms of bending strength and work of fracture have been prepared by in situ hot-pressing at 1600 8C for 4 h. In order to further improving the mechanical properties, SiC whiskers were added to Al2O3 layers as the 2ndlevel toughening agent. With the content of SiC whisker increasing, the bending strength and work of fracture showed a similar trend of increasing firstly and then decreasing. Hence, the optimal mechanical properties of 688 MPa for bending strength and 2583 J/m2 for work of fracture were obtained when the added content of SiC whisker was 20 wt%. These excellent properties should be attributed to 1st-level toughening mechanism (multilayer structural toughening), 2nd-level toughening mechanism (whisker toughening), and the synergy effect between them. Hence, adding SiC whiskers was an effective approach to improving the mechanical properties. # 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: B. Whisker; D. Al2O3; Ti3SiC2; Toughening mechanism; Multilayer ceramics 1. Introduction Ceramics are brittle and sometimes they fail catastrophically. Thislimitstheir applicationsin engineering. In orderto overcome the problem, studying of toughening becomes a very important research area in ceramics, especially structural ceramics. As a result, many toughening methods had been devised, researched and usedin ceramics, such aswhiskertoughening[1–3],long- and short-fiber toughening [4,5], dispersed rigid particle toughening [6], ZrO2 phasetransformationtoughening [7,8], and so on.These toughening methods were all effective for some ceramics, hereinto whiskers were used very widely. Otherwise, multilayer structural toughening was proved as an effective toughening mechanism [9–12]. Since the SiC/C multilayer ceramics was first developed by Clegg et al. [9], this toughening approach has been used in many systems, such as Si3N4/BN [10,11], SiC/C [9,12], Al2O3/ZrO2 [13], etc. and several 10-folds of fracture toughness and several 100-folds of work of fracture were achieved compared to the monolithic ceramics. Al2O3/Ti3SiC2 multilayer ceramics is a typical multilayer material, which possess good mechanical properties of 659 MPa for bending strength and 2159 J/m2 for work of fracture [14]. In recent years, synergy mechanism between two or more toughening methods was reported [15]. By this toughening mechanism, the toughness effect was usually larger than the additional effect brought by the individual toughening mechanisms. The all fore-mentioned toughening mechanisms could be used in synergy toughening design of ceramics by appropriate methods. In this paper, the SiC whiskers as 2nd-level toughening agent were added into Al2O3 layers in Al2O3/Ti3SiC2 multilayer ceramics. The 2nd-level toughening mechanism in the multilayer ceramics, the synergy effect between the multilevel toughening mechanisms and the fractural behavior of the whole materials will be described in this paper. www.elsevier.com/locate/ceramint Ceramics International 33 (2007) 385–388 * Corresponding author. Tel.: +86 10 89796112; fax: +86 10 89796118. E-mail address: Zanqingfeng@tsinghua.org.cn (Zan Qingfeng). 0272-8842/$32.00 # 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2005.10.007
386 Zan Qingfeng et al. /Ceramics International 33(2007)385-388 2. Experimental procedure 3. Results and discussion 2. 1. Materials and preparation 3. 1. Mechanical properties The Al2O,/Ti3SiC2 multilayer ceramics were prepared The mechanical properties of the Al2O3/Ti3SiC2 multilayer by in situ hot-pressing method according to a procedure ceramics, including bending strength and work of fracture, are described elsewhere [14]. The raw materials of Ti3 SiC2 layers shown in Table I and Fig. 2. With increasing the content of Sic were Ti, SiC and activated carbon powders. Otherwise, the whisker, the bending strength of the materials slightly increased Al2O3 layers were sintered from Al2O3 powders with MgO as firstly, and then decreased when the content of Sic whisker sintering aid and Sic whiskers as mechanical property exceeded 20 vol%. A similar trend was found for the work of is shown in Fig. 1. Firstly, powders of Al2O3(99.5% pure mechanical properties of 688 MPa for bending strength and Ceramic Co., China)with 0.3 wt% MgO(99.9% pure) and 2583 J/m- for work of fracture were obtained. Compared to the given certain quantities of SiC whiskers for the Al2O3 layer and multilayer without whisker (wO), the gain in of strength and powders of Ti(99.9% pure), SiC(99.9% pure) and activated work of fracture for materials w20 were about 4.4 and 19.6%0, carbon with the atomic ratio of 3: 1: 1 for the Ti3SiC2 layer were respectivel milled for 24 h in alcohol medium, respectively. Secondly, the Otherwise. it was found that when whisker content was green tapes of Al2O3 and Ti-SiC-C with thickness of about larger than 30 vol%, the specimens were broken after sintering 200 um both were manufactured by rolling after adding PVA, and cooling, which looked likely because of the residual glycerol and liquid affix into the raw powders. Then these stresses(as described in the following section in detail) ree vere dried in air and punched into rounds (0 50 mm). They were packed into a graphite die by turns of 3.2. Residual stresses analysis Al2O3 tapes and the Ti3SiC2 raw owders tape The green body underwent a conventional binder burnout through heating in For multilayer ceramics, especially with'strong'-interface, ing air. Finally, the multilayer ceramic was hot pressed the mechanical properties were reported to be influence 1600C for 4 h in Ar atmosphere with a pressure of about effectively by residual stress states [13], which was produced O MPa due to the thermal expansion mismatch between the interphase- layer and matrix-layer during cooling. The residual stresses 2.2. Tests and characterization would lead to cracking and three primary crack morphologies would be observed: transverse. longitudinal and debonding The specimens were sliced into test bars with the cracks if the residual stresses are large enough or the material dimensions of 4 mm x 3 mm x 36 mm for bending strength loaded. For multilayer materials, the transverse and debonding 30 mm for fracture toughness and the cracks are favorable to improve the toughness fracture work. Three-point bending test was carried out at room The residual stresses states in Al2O3/Ti3 SiC2 multilayer temperature with a span of 30 mm and a crosshead rate of ceramics without SiCw were already analyzed in our previous 0.5 mm/min. The work of fracture and fracture toughness were paper [16]. When SiC whiskers were added into Al2O3 layers, determined by the single-edge-notch-beam method (sENB)at the residual stresses states also changed. The residual room temperature with a span of 24 mm and a crosshead rate of stresses were calculated in the present work by the same 0.05 mm/min. All the tests were performed on A-2000 method, the parameters adopted in the calculation method are Shimadzu universal materials testing machine. The loads listed in Table 2. The sintering temperature was 1600C, and were applied perpendicular to the plane of laminates. The the thermal expansion coefficients of the Al2O3, Ti3 SiC2, TiC microstructure of the materials was observed by sEM and Sic whisker were assumed to be constant from room (CSM900) temperature to sintering temperature. The thickness of Al2O3 layer and Ti3 SiC2 layer were both about 100 um. For the two layers both containing two components, these mechanical parameters of each layer all need to be calculated by the rule of Ao3→Bmng Table 1 The mechanical properties of the Al2O,Ti]SiC2 multilayer ceramics with SiCw PVA+Glycerol+Liquid Paffi SiCw% Work of fracture (vol%) (MPa) Ti+SiC+C 0 659.53±47.3 2159±153 W10 674.38±25.6 0505 2341±146 Hot pressing Burning out 68359士34.1 2507±14 W20 Fig. 1. Flow chart for the preparation of Al,O,/Ti3 SiC, multilayer materials 68844±35.2 2583±142 W2 2326±135 with Sic whiskers 534.87±68.2
2. Experimental procedure 2.1. Materials and preparation The Al2O3/Ti3SiC2 multilayer ceramics were prepared by in situ hot-pressing method according to a procedure described elsewhere [14]. The raw materials of Ti3SiC2 layers were Ti, SiC and activated carbon powders. Otherwise, the Al2O3 layers were sintered from Al2O3 powders with MgO as sintering aid and SiC whiskers as mechanical property adjusting agent. The flow chart for the preparation of the multilayer materials is shown in Fig. 1. Firstly, powders of Al2O3 (99.5% pure, Jixin Ceramic Co., China) with 0.3 wt% MgO (99.9% pure) and given certain quantities of SiC whiskers for the Al2O3 layer and powders of Ti (99.9% pure), SiC (99.9% pure) and activated carbon with the atomic ratio of 3:1:1 for the Ti3SiC2 layer were milled for 24 h in alcohol medium, respectively. Secondly, the green tapes of Al2O3 and Ti-SiC-C with thickness of about 200 mm both were manufactured by rolling after adding PVA, glycerol and liquid paffix into the raw powders. Then these green tapes were dried in air and punched into rounds (Ø 50 mm). They were packed into a graphite die by turns of Al2O3 tapes and the Ti3SiC2 raw powders tapes. The green body underwent a conventional binder burnout through heating in flowing air. Finally, the multilayer ceramic was hot pressed at 1600 8C for 4 h in Ar atmosphere with a pressure of about 20 MPa. 2.2. Tests and characterization The specimens were sliced into test bars with the dimensions of 4 mm 3 mm 36 mm for bending strength and 4 mm 6 mm 30 mm for fracture toughness and the fracture work. Three-point bending test was carried out at room temperature with a span of 30 mm and a crosshead rate of 0.5 mm/min. The work of fracture and fracture toughness were determined by the single-edge-notch-beam method (SENB) at room temperature with a span of 24 mm and a crosshead rate of 0.05 mm/min. All the tests were performed on A-2000 Shimadzu universal materials testing machine. The loads were applied perpendicular to the plane of laminates. The microstructure of the materials was observed by SEM (CSM900). 3. Results and discussion 3.1. Mechanical properties The mechanical properties of the Al2O3/Ti3SiC2 multilayer ceramics, including bending strength and work of fracture, are shown in Table 1 and Fig. 2. With increasing the content of SiC whisker, the bending strength of the materials slightly increased firstly, and then decreased when the content of SiC whisker exceeded 20 vol%. A similar trend was found for the work of fracture expected for the improved extent. Therefore, when whisker content was about 20 vol% (W20), the optimal mechanical properties of 688 MPa for bending strength and 2583 J/m2 for work of fracture were obtained. Compared to the multilayer without whisker (W0), the gain in of strength and work of fracture for materials W20 were about 4.4 and 19.6%, respectively. Otherwise, it was found that when whisker content was larger than 30 vol%, the specimens were broken after sintering and cooling, which looked likely because of the residual stresses (as described in the following section in detail). 3.2. Residual stresses analysis For multilayer ceramics, especially with ‘strong’-interface, the mechanical properties were reported to be influenced effectively by residual stress states [13], which was produced due to the thermal expansion mismatch between the interphaselayer and matrix-layer during cooling. The residual stresses would lead to cracking and three primary crack morphologies would be observed: transverse, longitudinal and debonding cracks if the residual stresses are large enough or the material loaded. For multilayer materials, the transverse and debonding cracks are favorable to improve the toughness. The residual stresses states in Al2O3/Ti3SiC2 multilayer ceramics without SiCW were already analyzed in our previous paper [16]. When SiC whiskers were added into Al2O3 layers, the residual stresses states were also changed. The residual stresses were calculated in the present work by the same method, the parameters adopted in the calculation method are listed in Table 2. The sintering temperature was 1600 8C, and the thermal expansion coefficients of the Al2O3, Ti3SiC2, TiC and SiC whisker were assumed to be constant from room temperature to sintering temperature. The thickness of Al2O3 layer and Ti3SiC2 layer were both about 100 mm. For the two layers both containing two components, these mechanical parameters of each layer all need to be calculated by the rule of 386 Zan Qingfeng et al. / Ceramics International 33 (2007) 385–388 Fig. 1. Flow chart for the preparation of Al2O3/Ti3SiC2 multilayer materials with SiC whiskers. Table 1 The mechanical properties of the Al2O3/Ti3SiC2 multilayer ceramics with SiCW Samples SiCW% (vol%) Bending strength (MPa) Work of fracture (J/m2 ) W0 0 659.53 47.3 2159 153 W10 10 674.38 25.6 2341 146 W15 15 683.59 34.1 2507 143 W20 20 688.44 35.2 2583 142 W25 25 534.87 68.2 2326 135
Zan Qingfeng ef aL /Ceramics international 33(2007)385-388 3000 Table 3 Residual stresses of the AlO,Ti3SiC2 multilayer ceramics with SiCw Samples EA ET V 9Tg8Ec3 (GPa)(GPa) (x10-°/°C)(×10-6C)(MP 390.03210.3000.28.800 8.47 -121.2 W10409.03210.2900.28.370 8.47 37.8 W1541853210.2850.28.155 8.47 W20 428.03210.2800.27940 8.47 203.1 25437.53210.2750.27.725 8.47 287.3 447.03210.2700.27.510 8.47 372.3 1800 The residual compressive stresses in Al2O3 layer. SiCw(vol%) Fig. 2. Mechanical properties of the multilayer ceramics with SiC whiskers The toughening mechanisms induced by whisker in the multilayer ceramics, namely 2nd-level toughening mechan- sms, are similar to the toughening mechanisms in whisker mixture. And the calculated results containing the mechanical reinforced ceramic composites and have been studied ripely parameters and residual stresses of each layer are shown in they include crack deflection mechanism, crack bendin Table 3. With the content of whisker increasing, the residual mechanism, whisker pull-out mechanism, bridging mechanism, stresses in Al2O3 layer changed from tensile to compressive. micro-crack mechanism, and so on [1-5]. Fig. 3 shows the The residual compressive stresses could strengthen the Al2O3 microstructure of Al2O3 layer in the multilayer ceramics. The layer, thereby the fracture behavior and the toughening whiskers are observed homogeneously distributed and aligned mechanisms of the multilayer ceramics were also changed, directionally in two directions. The 2D texture of whiskers as described in Section 3.3 should be formed in the rolling procedure for green tape Otherwise, it is apparent from in Table 3 that when the preparation, and this was very useful to the whisker toughenin content of Sic whisker reaches 30 vol%, the residual tensile mechanisms. Otherwise, the pull-out mechanism selected as a stress in Ti3 SiC2 layers is up to 372 MPa. According to the representative one is shown in Fig. 4 papers about Ti3 SiC2 bulk ceramic [17, 18], the bending As we know, the toughening effects of the multilayered rength was reported to be only about 260-320 MPa which was structural toughening mechanisms depend strongly on the crack well-known higher than its tensile strength. Hence, the propagation path and the mechanical properties of the matrix multilayer ceramics with 30 vol% or more SiCw would be layer and interphase-layer [10]. When the Sic whiskers are broken by the residual stresses during sintering and following added into Al2O3 layers, the microstructure and mechanical Coo properties of the Al2O3 layer is changed at first. The change of mechanical properties of Al2O3 layer can influence the location 3.3. Toughening mechanisms and synergy effect of crack deflection and crack propagated path. In other words, it influences the 1st-level mechanisms. Otherwise. with the The high toughness of multilayer ceramics should be addition of Sic whiskers the residual stresses are changed as attributed to different kinds of toughening mechanisms. In the already analyzed above. From Table 2, the layers carry the AL2O,/Ti3 Sic2 multilayer ceramics with SiC whiskers, these residual compressive stress when whiskers are added. It makes toughening mechanisms could be: multilayered structural the Al2O3 layers difficult to fracture, and the crack is enforced toughening, whisker toughening and synergy effect by here ibefore two mechanisms The toughening mechanisms induced by multilayered structure,defined as 1st-level toughening mechanisms in this paper, have been investigated in recent years [9-14 they include crack deflection mechanism, bridging mechanism of interlocking layers, frictional sliding mechanism, and echanical parameters of Al2O. Ti SiC2, TiC and SiC whisker Materials Al,O3 Ti3SiC2 E(GPa) 0.20 0.20 10 CTE(10-°Cy 8.8 7.74 4.5 Fig 3. Fracture surface of the Al2O,Ti3 SiC2 multilayer ceramics with 20 vol% Assumed to be constant from room temperature to sintering temperature
mixture. And the calculated results containing the mechanical parameters and residual stresses of each layer are shown in Table 3. With the content of whisker increasing, the residual stresses in Al2O3 layer changed from tensile to compressive. The residual compressive stresses could strengthen the Al2O3 layer, thereby the fracture behavior and the toughening mechanisms of the multilayer ceramics were also changed, as described in Section 3.3. Otherwise, it is apparent from in Table 3 that when the content of SiC whisker reaches 30 vol%, the residual tensile stress in Ti3SiC2 layers is up to 372 MPa. According to the papers about Ti3SiC2 bulk ceramic [17,18], the bending strength was reported to be only about 260–320 MPa which was well-known higher than its tensile strength. Hence, the multilayer ceramics with 30 vol% or more SiCW would be broken by the residual stresses during sintering and following cooling procedures. 3.3. Toughening mechanisms and synergy effect The high toughness of multilayer ceramics should be attributed to different kinds of toughening mechanisms. In the Al2O3/Ti3SiC2 multilayer ceramics with SiC whiskers, these toughening mechanisms could be: multilayered structural toughening, whisker toughening and synergy effect by hereinbefore two mechanisms. The toughening mechanisms induced by multilayered structure, defined as 1st-level toughening mechanisms in this paper, have been investigated in recent years [9–14], they include crack deflection mechanism, bridging mechanism of interlocking layers, frictional sliding mechanism, and so on. The toughening mechanisms induced by whisker in the multilayer ceramics, namely 2nd-level toughening mechanisms, are similar to the toughening mechanisms in whisker reinforced ceramic composites and have been studied ripely, they include crack deflection mechanism, crack bending mechanism, whisker pull-out mechanism, bridging mechanism, micro-crack mechanism, and so on [1–5]. Fig. 3 shows the microstructure of Al2O3 layer in the multilayer ceramics. The whiskers are observed homogeneously distributed and aligned directionally in two directions. The 2D texture of whiskers should be formed in the rolling procedure for green tape preparation, and this was very useful to the whisker toughening mechanisms. Otherwise, the pull-out mechanism selected as a representative one is shown in Fig. 4. As we know, the toughening effects of the multilayered structural toughening mechanisms depend strongly on the crack propagation path and the mechanical properties of the matrixlayer and interphase-layer [10]. When the SiC whiskers are added into Al2O3 layers, the microstructure and mechanical properties of the Al2O3 layer is changed at first. The change of mechanical properties of Al2O3 layer can influence the location of crack deflection and crack propagated path. In other words, it influences the 1st-level mechanisms. Otherwise, with the addition of SiC whiskers the residual stresses are changed as already analyzed above. From Table 2, the layers carry the residual compressive stress when whiskers are added. It makes the Al2O3 layers difficult to fracture, and the crack is enforced Zan Qingfeng et al. / Ceramics International 33 (2007) 385–388 387 Fig. 2. Mechanical properties of the multilayer ceramics with SiC whiskers. Table 2 The mechanical parameters of Al2O3, Ti3SiC2, TiC and SiC whisker Materials Al2O3 Ti3SiC2 TiC SiCW E (GPa) 390 320 322 580 n 0.30 0.20 0.20 0.20 CTE (106 /8C)a 8.8 9.2 7.74 4.5 a Assumed to be constant from room temperature to sintering temperature. Table 3 Residual stresses of the Al2O3/Ti3SiC2 multilayer ceramics with SiCW Samples EA (GPa) ET (GPa) nA nT aA (106 /8C) aT (106 /8C) sR a (MPa) W0 390.0 321 0.300 0.2 8.800 8.47 121.2 W10 409.0 321 0.290 0.2 8.370 8.47 37.8 W15 418.5 321 0.285 0.2 8.155 8.47 120.0 W20 428.0 321 0.280 0.2 7.940 8.47 203.1 W25 437.5 321 0.275 0.2 7.725 8.47 287.3 W30 447.0 321 0.270 0.2 7.510 8.47 372.3 a The residual compressive stresses in Al2O3 layer. Fig. 3. Fracture surface of the Al2O3/Ti3SiC2 multilayer ceramics with 20 vol% SiC whiskers.
388 Zan Qingfeng et al. /Ceramics International 33(2007)385-388 Acknowledgement This work was supported by the National Science Foundation of China(NSFC)(( References [1] P.F. Becher, C. Hsueh. P. Angelini, T N. Tiegs. Toughening behavior in J. Am. Ceram. Soc. 71 (1988)1050-1061 [2] P.F. Becher, G.C. Wei, Development of Sic-whisker-reinforced ceramics, Am. Ceram. Soc. Bull. 64(1985)298-304 3]R V K. Sann. Fracture of whisker-reinforced ceramics. in Friedrich(Ed ) Application of Fracture Mechanics to Composite Materi- als, Elsevier Science Publisher B V, 1989. pp. 571-614 Fig. 4. Pull-out behavior of SiC whisker in AlO layers [4]B. wilshier, F Carreno, Deformation and failure processes during tensile reep of fiber and whisker reinforced SiC/Al2O3 composites, Mater. Sci. to propagating along the interface instead of through Al2O3 [5] PF Becher, in: K.S. Mazdiyasni(Ed. ) Fiber Reinforced Ceramic Com- layer, in other words, the resistance of longitudinal crack is posites. Noyes Publication, Park Ridge, NJ, USA, 1990. improved and the crack path is prolonged. On the other hand 间6]A. Goldstein,A.Si di, Al2O/TiC based metal cutting tools by some whiskers insert adjacent Ti3 SiC2 layers ineluctably. Some microwave sintering followed by hot isostatic pressing, J. Am. Ceram. Soc.83(20001530-1532. of the whiskers possibly act as a bridge bet ween layer and they 7l ,G: cvas AH. He. Transform atis toughening in ceramics proving the propagating resistance of transverse crack. The (1980)241-248. changes of the toughening mechanisms described above are [8] T H.J. Hannink, P.M. Kelly, B.C. Muddle, Transformation toughening in rconia-containing ceramics, J. Am. Ceram Soc. 83(2000)461-487 different from the individual toughening mechanisms by [9] W.J. Clegg, K Kendall, N.M. Alford, T.W. Button, J.D. Birchall,A simple multilayered structure or whisker toughening. Hence, there way to make tough ceramics, Nature 347(1990)455-457. effect between the lst-level and 2nd-level [10] D Kovar, M D. Thouless, J w. Halloran, Crack deflection and propagation toughening mechanisms in layered silicon nitride/boron nitride ceramics, J. Am. Ceram. Soc. 81 According to the toughness data of the multilayer ceramics (1998)1004-1012. [11 C.A. Wang. Y Huang, Q F. Zan, L H. Zou, S.Y. Cai, Control of composi- shown in Table l, the greatly improvement of work of fracture on and structure in laminated silicon nitride/boron nitride composites, J Am. Ceran.Soc.8502002)2457-246 multilayer structural toughening mechanisms and their synergy [121 L Zhang, V.D. Krstic, High toughness silicon carbide/graphite laminar effect [13] B. Hatton, P.S. Nicholson, Design and fracture of layered Al2O/TZ3Y mposites produced b 4. Conclusions [14] Q.F. Zan, C.A. Wang, Y. Huang, C.W. Li, S.Q. Li, Preparation of Al2O3/ By adding Sic whiskers into Al2O3 layers, the mechanical Ti3 SiC2 multilayer materials by in-situ synthesis, Key Eng. Mater. 224- properties of multilayered ceramics is obviously improved, the 226(2002)409-412 ptimal mechanical properties being obtained for 20 vol% [15] W.H. Tuan, J.K. Guo, Toughening ceramics by adding two toughening SiCw addition. Hence, the 2nd-level toughening by whiskers is [16)QF. Zan, C.A. Wang Y. Huang. S K Zhao, C.w. Li, The interface and an effective method to multilayer ceramics.The synergy effect interface layer in the AlO,/Ti3 SiC2 multilayer composites by in-situ between whisker toughening and multilayer structural tough synthesis, Mater. Lett. 57(2003)3826-3832. ening was induced in the multilayer ceramics with Sic [17] M W Barsoum, T El-Raghy, Synthesis and characterization of a remark able ceramic: Ti,,, J. Am. Ceram Soc. 79(1996)1953-1956 whiskers,and the improvement of toughness was attributed to [18)T El-Raghy, MWBarsoum,A.Zavaliangos,SRKalidindi,Processing the interaction between whisker toughening, multilayer and mechanical properties of Ti,SiC2. IL. Effect of grain size and structural toughening and synergy effect deformation temperature, J. Am. Ceram Soc. 82(1999)2855-2860
to propagating along the interface instead of through Al2O3 layer, in other words, the resistance of longitudinal crack is improved and the crack path is prolonged. On the other hand, some whiskers insert adjacent Ti3SiC2 layers ineluctably. Some of the whiskers possibly act as a bridge between layers, and they can bridge the transverse crack propagating in the interface, improving the propagating resistance of transverse crack. The changes of the toughening mechanisms described above are different from the individual toughening mechanisms by multilayered structure or whisker toughening. Hence, there is a synergy effect between the 1st-level and 2nd-level toughening mechanisms. According to the toughness data of the multilayer ceramics shown in Table 1, the greatly improvement of work of fracture reflects the interaction of the whisker toughening mechanisms, multilayer structural toughening mechanisms and their synergy effect. 4. Conclusions By adding SiC whiskers into Al2O3 layers, the mechanical properties of multilayered ceramics is obviously improved, the optimal mechanical properties being obtained for 20 vol% SiCW addition. Hence, the 2nd-level toughening by whiskers is an effective method to multilayer ceramics.The synergy effect between whisker toughening and multilayer structural toughening was induced in the multilayer ceramics with SiC whiskers, and the improvement of toughness was attributed to the interaction between whisker toughening, multilayer structural toughening and synergy effect. Acknowledgement This work was supported by the National Science Foundation of China (NSFC) (Grant no. 59982004). References [1] P.F. Becher, C. Hsueh, P. Angelini, T.N. Tiegs, Toughening behavior in whisker-reinforced ceramic matrix composites, J. Am. Ceram. Soc. 71 (1988) 1050–1061. [2] P.F. Becher, G.C. Wei, Development of SiC-whisker-reinforced ceramics, Am. Ceram. Soc. Bull. 64 (1985) 298–304. [3] R. Warren, V.K. Sarin, Fracture of whisker-reinforced ceramics, in: K. Friedrich (Ed.), Application of Fracture Mechanics to Composite Materials, Elsevier Science Publisher B.V., 1989, pp. 571–614. [4] B. Wilshier, F. Carreno, Deformation and failure processes during tensile creep of fiber and whisker reinforced SiC/Al2O3 composites, Mater. Sci. Eng. A272 (1999) 38–44. [5] P.F. Becher, in: K.S. Mazdiyasni (Ed.), Fiber Reinforced Ceramic Composites, Noyes Publication, Park Ridge, NJ, USA, 1990. [6] A. Goldstein, A. Singurindi, Al2O3/TiC based metal cutting tools by microwave sintering followed by hot isostatic pressing, J. Am. Ceram. Soc. 83 (2000) 1530–1532. [7] A.G. Evans, A.H. Heuer, Transformation toughening in ceramics: martensitic transformations in crack-tip stress fields, J. Am. Ceram. Soc. 63 (1980) 241–248. [8] T.H.J. Hannink, P.M. Kelly, B.C. Muddle, Transformation toughening in zirconia-containing ceramics, J. Am. Ceram. Soc. 83 (2000) 461–487. [9] W.J. Clegg, K. Kendall, N.M. Alford, T.W. Button, J.D. Birchall, A simple way to make tough ceramics, Nature 347 (1990) 455–457. [10] D. Kovar, M.D. Thouless, J.W. Halloran, Crack deflection and propagation in layered silicon nitride/boron nitride ceramics, J. Am. Ceram. Soc. 81 (1998) 1004–1012. [11] C.A. Wang, Y. Huang, Q.F. Zan, L.H. Zou, S.Y. Cai, Control of composition and structure in laminated silicon nitride/boron nitride composites, J. Am. Ceram. Soc. 85 (2002) 2457–2461. [12] L. Zhang, V.D. Krstic, High toughness silicon carbide/graphite laminar composite by slip casting, Theo. Appl. Fract. Mech. 24 (1995) 13–19. [13] B. Hatton, P.S. Nicholson, Design and fracture of layered Al2O3/TZ3Y composites produced by electrophoretic deposition, J. Am. Ceram. Soc. 84 (2001) 571–576. [14] Q.F. Zan, C.A. Wang, Y. Huang, C.W. Li, S.Q. Li, Preparation of Al2O3/ Ti3SiC2 multilayer materials by in-situ synthesis, Key Eng. Mater. 224– 226 (2002) 409–412. [15] W.H. Tuan, J.K. Guo, Toughening ceramics by adding two toughening agents, Key Eng. Mater. 224–226 (2002) 317–320. [16] Q.F. Zan, C.A. Wang, Y. Huang, S.K. Zhao, C.W. Li, The interface and interface layer in the Al2O3/Ti3SiC2 multilayer composites by in-situ synthesis, Mater. Lett. 57 (2003) 3826–3832. [17] M.W. Barsoum, T. El-Raghy, Synthesis and characterization of a remarkable ceramic: Ti3SiC2, J. Am. Ceram. Soc. 79 (1996) 1953–1956. [18] T. El-Raghy, M.W. Barsoum, A. Zavaliangos, S.R. Kalidindi, Processing and mechanical properties of Ti3SiC2. II. Effect of grain size and deformation temperature, J. Am. Ceram. Soc. 82 (1999) 2855–2860. 388 Zan Qingfeng et al. / Ceramics International 33 (2007) 385–388 Fig. 4. Pull-out behavior of SiC whisker in Al2O3 layers
