MATERIALS HIENGE& ENGIEERING ELSEVIER Materials Science and Engineering A 443(2007)296-300 www.elsevier.com/locate/msea Short communication Improving the mechanical properties of Al2O3 /Ni laminated composites by adding Ni particles in Al2O3 layers Kai Hui zuo, Dong Liang Jiang, Qing Ling Lin, Yu-ping Zeng The State Key Lab of High Performance Ceramics and Superfine Structure, Shanghai institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, PR China Received 9 June 2006; received in revised form 11 August 2006: accepted 15 September 2006 Abstract The(Al2O3+Ni)composite,AlO3+NiNi and Al2O3/(Al2O3+Ni)/Ni laminated materials were prepared by aqueous tape casting and hot pressing. Results indicated that the(Al2O3+Ni) composite had higher strength and fracture toughness than those of pure Al2O3. The fracture ghness of(Al2O3 +Ni)Ni and AlO3/(Al2O3+Ni/Ni laminated materials was higher than not only those of pure Al2O,, but also those of Al2O3/Ni laminar with the same layer numbers and thickness ratio. It was found that the toughness of the Al2O3(Al2O3+Ni/Ni laminated aterial with five layers and layer thickness ratio=2 could reach 16.10 MPam", which were about 4.6 times of pure Al2O3. The strength and toughness of the(Al2O, +Ni)/Ni laminated material with three layers and layer thickness ratio=2 could reach 417.41 MPa and 12.42 MPam".It indicated the material had better mechanical proper C 2006 Elsevier B. v. all rights reserved Keywords: Multilayers; Mechanical properties; Fracture 1. Introduction second phases into the ceramic matrix is another way to increase the toughness and strength of ceramic [12-16]. The most effec- Ceramics is a kind of important structure material due to its tive toughening mechanism through addition of metallic is that high strength, low density and other advantages. But the lack of cracking bridging of damage tolerance ability constrains its applications. Lami- We have fabricated Al2O3/Ni laminated materials prepared nated composites as one of the main way for improving the by aqueous tape casting and hot pressing before [9]. All brittleness of ceramics are getting more and more attention Al2 O3/Ni laminated composites had higher fracture toughness from the biomimetic point. Clegg and co-workers [1-4] had than that of pure Al2O3. But the increase of strength of Al2O3/N roduced laminated SiC with graphite interface layers, which laminar is limited. Sometimes, the strength of Al2O3/Ni is ever composite showed stepped stress-strain behavior with higher lower than that of pure AlO3. In the present study, we com- parent toughness and work of fracture than monolithic SiC. bined ceramic/metal laminated structure and(ceramic+metal) The ceramic/metal composite as a part of laminated composites mixture composite for increasing the toughness and strength combines some advantages of the ceramics and metals [5-8. together. As far as we knew, few works on these studies have When cracks stretch to the metal interlayer, due the ductility of been reported the metal, they can be deflected, bridged, etc, which generally mprove the toughness of the composition [9, 10]. The residual 2. Experimental procedure compressive stress, which is caused by the mismatch of thermal expansion of ceramic and metal, also contributes to the incre- Al2O3(Shanghai Wusong Fertilizer Factory, China) with the mental strength and toughness [9, Il]. Incorporation of metallic particle size of about 0.3 um and Ni electrolytic powder with the particle size of about 1-2 um(Shanghai Jiuling Smelting Co Ltd, China)were used as the starting materials. The Al2O3 Corresponding author. Tel. +86 21 5241 2165: fax: +86 21 5241 3903 Ni and(Al2O3+ Ni) green sheets were produced by aq omailaddresses:clothwhite@yahoo.com.cn(KH.Zuo), tape casting. The fabrication details of Al2O3 and Ni green dejiang@ sunm shcc ac cn(D L Jiang) sheets have been described in another paper [17]. Briefly, the 0921-5093 )6 Elsevier B v. All rights reserved
Materials Science and Engineering A 443 (2007) 296–300 Short communication Improving the mechanical properties of Al2O3/Ni laminated composites by adding Ni particles in Al2O3 layers Kai Hui Zuo, Dong Liang Jiang ∗, Qing Ling Lin, Yu-ping Zeng The State Key Lab of High Performance Ceramics and Superfine Structure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, PR China Received 9 June 2006; received in revised form 11 August 2006; accepted 15 September 2006 Abstract The (Al2O3 + Ni) composite, (Al2O3 + Ni)/Ni and Al2O3/(Al2O3 + Ni)/Ni laminated materials were prepared by aqueous tape casting and hot pressing. Results indicated that the (Al2O3 + Ni) composite had higher strength and fracture toughness than those of pure Al2O3. The fracture toughness of (Al2O3 + Ni)/Ni and Al2O3/(Al2O3 + Ni)/Ni laminated materials was higher than not only those of pure Al2O3, but also those of Al2O3/Ni laminar with the same layer numbers and thickness ratio. It was found that the toughness of the Al2O3/(Al2O3 + Ni)/Ni laminated material with five layers and layer thickness ratio = 2 could reach 16.10 MPa m1/2, which were about 4.6 times of pure Al2O3. The strength and toughness of the (Al2O3 + Ni)/Ni laminated material with three layers and layer thickness ratio = 2 could reach 417.41 MPa and 12.42 MPa m1/2. It indicated the material had better mechanical property. © 2006 Elsevier B.V. All rights reserved. Keywords: Multilayers; Mechanical properties; Fracture 1. Introduction Ceramics is a kind of important structure material due to its high strength, low density and other advantages. But the lack of damage tolerance ability constrains its applications. Laminated composites as one of the main way for improving the brittleness of ceramics are getting more and more attention from the biomimetic point. Clegg and co-workers [1–4] had produced laminated SiC with graphite interface layers, which composite showed stepped stress–strain behavior with higher apparent toughness and work of fracture than monolithic SiC. The ceramic/metal composite as a part of laminated composites combines some advantages of the ceramics and metals [5–8]. When cracks stretch to the metal interlayer, due the ductility of the metal, they can be deflected, bridged, etc., which generally improve the toughness of the composition [9,10]. The residual compressive stress, which is caused by the mismatch of thermal expansion of ceramic and metal, also contributes to the incremental strength and toughness [9,11]. Incorporation of metallic ∗ Corresponding author. Tel.: +86 21 5241 2165; fax: +86 21 5241 3903. E-mail addresses: clothwhite@yahoo.com.cn (K.H. Zuo), dljiang@sunm.shcnc.ac.cn (D.L. Jiang). second phases into the ceramic matrix is another way to increase the toughness and strength of ceramic [12–16]. The most effective toughening mechanism through addition of metallic is that of cracking bridging. We have fabricated Al2O3/Ni laminated materials prepared by aqueous tape casting and hot pressing before [9]. All Al2O3/Ni laminated composites had higher fracture toughness than that of pure Al2O3. But the increase of strength of Al2O3/Ni laminar is limited. Sometimes, the strength of Al2O3/Ni is ever lower than that of pure Al2O3. In the present study, we combined ceramic/metal laminated structure and (ceramic + metal) mixture composite for increasing the toughness and strength together. As far as we knew, few works on these studies have been reported. 2. Experimental procedure Al2O3 (Shanghai Wusong Fertilizer Factory, China) with the particle size of about 0.3 m and Ni electrolytic powder with the particle size of about 1–2m (Shanghai Jiuling Smelting Co., Ltd., China) were used as the starting materials. The Al2O3, Ni and (Al2O3 + Ni) green sheets were produced by aqueous tape casting. The fabrication details of Al2O3 and Ni green sheets have been described in another paper [17]. Briefly, the 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.09.055
K.H. Zuo et al. Materials Science and Engineering A 443(2007)296-300 Subsequently, organic additives were removed at 600C for 1.5 h in a vacuum. Then the laminar was sintered by hot pressing at 25 MPa under an argon atmosphere at 1400C for I h Samples were cut out of sintered stacks parallel to the lam inated layers. Three-points bending strength was determined at room temperature with a crosshead speed of 0.5 mm min" ( Fig. 2(a)) using Instron-1195. The fracture toughness was achieved by the single-edge notched beam test with a crosshead illustrations of laminated materials: (a)A1,O,/(A1,0,+Niy speed of 0.05 mm min-(Fig. 2(b). The straight edge notch Ni laminar and(b)(Al2O3+Ni/Ni laminar was introduced by incircle cutter with a 0.2 mm thick diamond wheel. The relative notch depth to the height of the sample was (Al2O3+Ni)green sheet was fabricated by adding 20 wt% Ni maintained at O.5. Surface properties and microstructure char on the Al2O3 powder)in the Al2O3 slurry. acterizations were measured by optical microscopy(Olympus The thickness of green tapes was in the range of 200-500 um. BX5IM, Japan)and SEM (SM-6700F, JEOL Symmetrical laminated composites were fabricated by period- ically stacking the Al2O3, Ni and(Al2O3+ Ni)green sheets 3. Results and discussion gether. The schematic illustrations of (AlO3+Ni/Ni and AlO3/(Al2O3+Ni)/Ni laminated material were shown in Fig. 1. 3.1. Microstructure and mechanical properties of the Each layer was stacked with some Al2O3 or Ni or(Al2O3+Ni) (Al203+ Ni) composite green sheets. Pure Al2O3 was also stacked using Al2O3 green sheets. a parameter of the layer thickness ratio x was used The SEM micrographs of the(Al2 O3+Ni)com For the AlO3/Ni laminate, x=he/hm (he and hm were the shown in Fig 3. Ni grains forming big aggregates with the size thickness of ceramic and metal layer, respectively). For the about 24 um non-uniformly distribute among AlO3 particles (Al2O3+Ni)/Ni laminate, x was defined as the ratio of the More researches should be done to improve the uniformly distri Al2O3+Ni) layer thickness to the Ni layer thickness. And for bution of Ni among Al2O3 particles. Table 1 is the mechanical the AlO3/(Al2O3+Ni)/Ni laminate, x1= hAl203/h(A1 03 +Ni) property of pure Al2O3 and the(Al2O3+Ni)composite.The and x2=hAl,,/hNi. The Al203/Ni composite with three lay- strength and fracture toughness of the(Al2O3+ Ni)composite ers and x=2 has the higher fracture toughness and lower are 447. 8 MPa and 3. 6 MPa 2, respectively. It indicates that strength. The Al2O3/Ni composite with nine layers and x=7 the mechanical property of the(Al2O3+ Ni)composite is better has the higher strength and lower toughness [9]. So in order than that of pure Al2O3 ceramic to obtain composite with higher toughness and strength, the The mismatch of thermal expansion coefficient of Ni and (AlO3 +Ni)/Ni laminate with three or nine layers and x=2 or Al2O3 results in generating the residual stresses in the Ni par 7 was fabricated ticles and matrix particles during cooling process. There is a residual radial tensile stress and radial tangential compressiv Mechanical properties of pure Al2O3 and the(Al2 O3+Ni)composite Material Strength(MPa) Fracture toughness(MPam Fig. 2. Schematic illustrations of strength and fracture toughness of laminated Al,O3 35441±23.24 3.47±0.12 materials measured by the three-point bending method: (a) strength and( b) (AlO3+Ni 447.77±18.72 3.57±0.15 acture toughness Fig 3. SEM micrographs of theAl2 O3+Nicomposite
K.H. Zuo et al. / Materials Science and Engineering A 443 (2007) 296–300 297 Fig. 1. Schematic illustrations of laminated materials: (a) Al2O3/(Al2O3 + Ni)/ Ni laminar and (b) (Al2O3 + Ni)/Ni laminar. (Al2O3 + Ni) green sheet was fabricated by adding 20 wt% Ni particles (based on the Al2O3 powder) in the Al2O3 slurry. The thickness of green tapes was in the range of 200–500 m. Symmetrical laminated composites were fabricated by periodically stacking the Al2O3, Ni and (Al2O3 + Ni) green sheets together. The schematic illustrations of (Al2O3 + Ni)/Ni and Al2O3/(Al2O3 + Ni)/Ni laminated material were shown in Fig. 1. Each layer was stacked with some Al2O3 or Ni or (Al2O3 + Ni) green sheets. Pure Al2O3 was also stacked using Al2O3 green sheets. A parameter of the layer thickness ratio x was used. For the Al2O3/Ni laminate, x = hc/hm (hc and hm were the thickness of ceramic and metal layer, respectively). For the (Al2O3 + Ni)/Ni laminate, x was defined as the ratio of the (Al2O3 + Ni) layer thickness to the Ni layer thickness. And for the Al2O3/(Al2O3 + Ni)/Ni laminate, x1 = hAl2O3 /h(Al2O3+Ni) and x2 = hAl2O3 /hNi. The Al2O3/Ni composite with three layers and x = 2 has the higher fracture toughness and lower strength. The Al2O3/Ni composite with nine layers and x = 7 has the higher strength and lower toughness [9]. So in order to obtain composite with higher toughness and strength, the (Al2O3 + Ni)/Ni laminate with three or nine layers and x = 2 or 7 was fabricated. Fig. 2. Schematic illustrations of strength and fracture toughness of laminated materials measured by the three-point bending method: (a) strength and (b) fracture toughness. Subsequently, organic additives were removed at 600 ◦C for 1.5 h in a vacuum. Then the laminar was sintered by hot pressing at 25 MPa under an argon atmosphere at 1400 ◦C for 1 h. Samples were cut out of sintered stacks parallel to the laminated layers. Three-points bending strength was determined at room temperature with a crosshead speed of 0.5 mm min−1 (Fig. 2(a)) using Instron-1195. The fracture toughness was achieved by the single-edge notched beam test with a crosshead speed of 0.05 mm min−1 (Fig. 2(b)). The straight edge notch was introduced by incircle cutter with a 0.2 mm thick diamond wheel. The relative notch depth to the height of the sample was maintained at 0.5. Surface properties and microstructure characterizations were measured by optical microscopy (Olympus BX51M, Japan) and SEM (JSM-6700F, JEOL). 3. Results and discussion 3.1. Microstructure and mechanical properties of the (Al2O3 + Ni) composite The SEM micrographs of the (Al2O3 + Ni) composite are shown in Fig. 3. Ni grains forming big aggregates with the size about 2–4m non-uniformly distribute among Al2O3 particles. More researches should be done to improve the uniformly distribution of Ni among Al2O3 particles. Table 1 is the mechanical property of pure Al2O3 and the (Al2O3 + Ni) composite. The strength and fracture toughness of the (Al2O3 + Ni) composite are 447.8 MPa and 3.6 MPa m1/2, respectively. It indicates that the mechanical property of the (Al2O3 + Ni) composite is better than that of pure Al2O3 ceramic. The mismatch of thermal expansion coefficient of Ni and Al2O3 results in generating the residual stresses in the Ni particles and matrix particles during cooling process. There is a residual radial tensile stress and radial tangential compressive Table 1 Mechanical properties of pure Al2O3 and the (Al2O3 + Ni) composite Material Strength (MPa) Fracture toughness (MPa m1/2) Al2O3 354.41 ± 23.24 3.47 ± 0.12 (Al2O3 + Ni) 447.77 ± 18.72 3.57 ± 0.15 Fig. 3. SEM micrographs of the (Al2O3 + Ni) composite.
K.H. Zuo et al. / Materials Science and Engineering A 443(2007)296-300 stress surrounding the Al2O3 particles. Cracks are expected to 3.2. Microstructure and mechanical properties of propagate in a direction parallel to the axis of the compressive (A203+NiVNi and Al2 O3/Al203+ Ni)Ni laminated stress and perpendicular to the axis of the tensile stress in the materials matrix(Fig 4(a))[12], which will increase the extended path of cracks and resistant force of crack expansion(Fig 4(b)). These Fig. 5 are the optical micrographs of parts of the are other reasons for the higher strength and toughness of the whole(Al2O3+Ni)/Ni laminar with 29 layers and Al2O3/ A12O3+Ni) composite Al2O3+Ni)/Ni laminar with 5 layers. Fig. 5 shows that there For the aggregate of Ni existences among the Al2O3/Al2O3 are no cracks, delaminations, and distortion in materials. It indi- particle boundaries or at the triple junctions of Al2O3 particles, a cates that tape casting combined with hot pressing can fabricate compressive stress will be developed in the AlO3/Al2O3 parti- (A12O3+Ni)/Ni and Al2O3/(Al2O3+Ni)/Ni laminated materi- cle boundaries, due to the residual radial tensile stress of Al O3 als. particles. This will strengthen the grain boundaries of Al2O3 Table 2 is the mechanical property of(Al2O3+Ni)/Ni and particles and cause some transcrystalline fractures phenomena, Al2O3/(Al2O3+ Ni)/Ni laminated materials. The fracture tough- which also can increase the strength and fracture toughness of ness of all laminated materials is not only higher than that of the(al O3+ Ni) mixture material pure Al2O3 and(Al2O3+Ni)composite, but also higher than Micro-crack will develop when the grain diameter(d)of that of Alz O3/Ni laminar with the same layer number and x. The Ni is bigger than the critical diameter(dc). According to strength and toughness of (Al2O3+ Ni)/Ni with three layers and the results of Davidge and Green [18 de can calculated as x=2 are 417. 41 MPa and 12.42 2, which is the 1.2 and following: 3.5 times of pure Al2O3, whose mechanical property is the best. The Al2O3/(Al2O3+Ni)/Ni laminar with five layers and x=2 d e has the highest fracture toughness, which is 4.6 times of pur P[(+Ⅷm)Em)+(2(1-2v)Ep) AlO3. Adding of the Ni particles in AlO layers is the reason where ys and P are surface energy and load, respectively. For for (Al203+Ni)/Ni and Al2O3/(Al203+ Ni)/Ni laminated ys of Al2 O3/meta is 1.5-2.3J/", de is 0. 48-0. um. The d of materials having higher strength and toughness than those of Ni in the(AlO3+ Ni) composite is bigger thane, micro-cracks Al O3/Ni laminar with the same layer number and x.The reason will develop, which also can improve the strength and toughness of higher toughness of the Al2O3/Ni laminated material has been of the(Al2O3+ Ni)composite discussed in another paper [9]. Fig. 6 is the load-displacement curves of laminated materials. The (AlO3+Ni) material exhibits catastrophic fracture behavior like that of pure Al2O Tensile (a) The little kicks in the cures of the(Al2O3+Ni)composite are Crack characterized by cracks deflection, cracks bridging caused by ni particles in Al2O3 matrix. Al2O3/Ni laminar, (Al2O3+Ni)/Ni laminar and Al2O3/(Al2O3+ Ni)/Ni laminar all display the Compressive Fig. 5. Optical graphs of ceramic and metal laminated materials:(a Fig. 4. Schematic of crack-particle interaction(a), and SEM image of a crack (Al2O3+Ni)/Ni and( b)Al2O3/(Al2O3+Ni /Ni Graphs are parts of the whole in the(Al2O3+Ni) mixture material(b)
298 K.H. Zuo et al. / Materials Science and Engineering A 443 (2007) 296–300 stress surrounding the Al2O3 particles. Cracks are expected to propagate in a direction parallel to the axis of the compressive stress and perpendicular to the axis of the tensile stress in the matrix (Fig. 4(a)) [12], which will increase the extended path of cracks and resistant force of crack expansion (Fig. 4(b)). These are other reasons for the higher strength and toughness of the (Al2O3 + Ni) composite. For the aggregate of Ni existences among the Al2O3/Al2O3 particle boundaries or at the triple junctions of Al2O3 particles, a compressive stress will be developed in the Al2O3/Al2O3 particle boundaries, due to the residual radial tensile stress of Al2O3 particles. This will strengthen the grain boundaries of Al2O3 particles and cause some transcrystalline fractures phenomena, which also can increase the strength and fracture toughness of the (Al2O3 + Ni) mixture material. Micro-crack will develop when the grain diameter (d) of Ni is bigger than the critical diameter (dc). According to the results of Davidge and Green [18], dc can calculated as following: dc = 8γs P2[((1 + νm)/Em) + (2(1 − 2νp)/Ep)] where γs and P are surface energy and load, respectively. For γs of Al2O3/meta is 1.5–2.3 J/m2, dc is 0.48–0.73m. The d of Ni in the (Al2O3 + Ni) composite is bigger than dc, micro-cracks will develop, which also can improve the strength and toughness of the (Al2O3 + Ni) composite. Fig. 4. Schematic of crack–particle interaction (a), and SEM image of a crack in the (Al2O3 + Ni) mixture material (b). 3.2. Microstructure and mechanical properties of (Al2O3 + Ni)/Ni and Al2O3/(Al2O3 + Ni)/Ni laminated materials Fig. 5 are the optical micrographs of parts of the whole (Al2O3 + Ni)/Ni laminar with 29 layers and Al2O3/ (Al2O3 + Ni)/Ni laminar with 5 layers. Fig. 5 shows that there are no cracks, delaminations, and distortion in materials. It indicates that tape casting combined with hot pressing can fabricate (Al2O3 + Ni)/Ni and Al2O3/(Al2O3 + Ni)/Ni laminated materials. Table 2 is the mechanical property of (Al2O3 + Ni)/Ni and Al2O3/(Al2O3 + Ni)/Ni laminated materials. The fracture toughness of all laminated materials is not only higher than that of pure Al2O3 and (Al2O3 + Ni) composite, but also higher than that of Al2O3/Ni laminar with the same layer number and x. The strength and toughness of (Al2O3 + Ni)/Ni with three layers and x = 2 are 417.41 MPa and 12.42 MPa m1/2, which is the 1.2 and 3.5 times of pure Al2O3, whose mechanical property is the best. The Al2O3/(Al2O3 + Ni)/Ni laminar with five layers and x = 2 has the highest fracture toughness, which is 4.6 times of pure Al2O3. Adding of the Ni particles in Al2O3 layers is the reason for (Al2O3 + Ni)/Ni and Al2O3/(Al2O3 + Ni)/Ni laminated materials having higher strength and toughness than those of Al2O3/Ni laminar with the same layer number and x. The reason of higher toughness of the Al2O3/Ni laminated material has been discussed in another paper [9]. Fig. 6 is the load–displacement curves of laminated materials. The (Al2O3 + Ni) material exhibits catastrophic fracture behavior like that of pure Al2O3. The little kicks in the cures of the (Al2O3 + Ni) composite are characterized by cracks deflection, cracks bridging caused by Ni particles in Al2O3 matrix. Al2O3/Ni laminar, (Al2O3 + Ni)/Ni laminar and Al2O3/(Al2O3 + Ni)/Ni laminar all display the Fig. 5. Optical graphs of ceramic and metal laminated materials: (a) (Al2O3 + Ni)/Ni and (b) Al2O3/(Al2O3 + Ni)/Ni. Graphs are parts of the whole samples.
K.H. Zuo et al. Materials Science and Engineering A 443(2007)296-300 Mechanical properties of ceramic/metal laminated materials Laminated material Strength(MPa) Fracture toughness(MPam2 Number of layers Laver thickness ratio (Al2 O3+NiNi 士21133士12 AlO3(Al O3+Ni/Ni 16.10±1.71 Al2O3/Ni AlO3/Ni 433.74±19.28 4.62士 AlO3 5441±23.24 3.47±0.12 0015 Displacement(mm Displcement(mm) LO(ALO+Ni)Ni laminar with 5 layers and x-2 00000100150200250 Displcement(mm) Displacement (mm) O/Ni with layers and- 000040.080.120.160.2 Fig. 6. Displacement-load curves of some materials
K.H. Zuo et al. / Materials Science and Engineering A 443 (2007) 296–300 299 Table 2 Mechanical properties of ceramic/metal laminated materials Laminated material Strength (MPa) Fracture toughness (MPa m1/2) Composition Number of layers Layer thickness ratio (Al2O3 + Ni)/Ni 3 2 417.41 ± 20.12 12.42 ± 1.71 (Al2O3 + Ni)/Ni 29 7 466.34 ± 25.31 5.73 ± 0.22 Al2O3/(Al2O3 + Ni)/Ni 5 2a 293.35 ± 41.08 16.10 ± 1.71 Al2O3/Ni 3 2 219.69 ± 17.58 8.24 ± 0.41 Al2O3/Ni 29 7 433.74 ± 19.28 4.62 ± 0.24 Al2O3 – – 354.41 ± 23.24 3.47 ± 0.12 a x1 = x2 = 2. Fig. 6. Displacement–load curves of some materials
K.H. Zuo et al. / Materials Science and Engineering A 443(2007)296-300 Because of the crack deflection by residual stress and Ni par ticles, and crack bridging by Ni particles, the strength and fracture toughness of(Al2O3+Ni) composite are higher than those of pure Al2O3. The toughness of (Al2O3+Ni)/Ni and AlO3/(Al2O3 +Ni)/Ni laminated materials are higher than not only that of pure Al2O3, but also that of Al2O3/Ni with the same layer number and x, due to the toughen mechanism of laminated structure and composite with the second-phase. The strength and toughness of (Al2O3+Ni)/Ni with three layers and x=2 417. MPa and 12.42 MPam/2 which are 1.2 and 3.5 times of pure Al2O3, whose mechanical property of the material is good The highest toughness of the AlO3/(Al2O3+ Ni)/Ni laminated material is 16.10 2, which is the 4.6 times of that of pure AlO3 Acknowledgments This work is supported by the Science and Technology Com- mittee of Shanghai Municipal under the project No. O2DJ14065 Fig.7. Optical graphs of laminated materials after measuring fracture strength, and by Chinese Academy of Science under the project No indicating the metal layers deform greatly. ICGCX2-SW-602-3 step-wise load behavior, characterized of non-catastrophic References fracture Unlike the load-displacement cure of usually composite [1]wJ.Clegg, KKendall,NM.Alford, TWButton,JD.Birchall,Nature materials, such as Al2O3/Ni laminar with three layers andx=7, ( London)347(4)(1990)455-457. the displacement-load cures of (Al2O3+ Ni)/Ni with three lay 2] w.J. Clegg, Acta Metall. Mater. 40(11)(1992)3085-3093 ers and x= 2 and Al2O3/(AlO3+Ni)/Ni laminar with five layers [3] A.J. Phillipps, w.J. Clegg, T W. Clyne, Acta Metall. Mater. 41(3)(1993) 805-817. and x=2 arise after the outermost ceramic layer breaking(cor- [4]A J Phillipps, w.J. Clegg, T.W. Clyne, Composites 24(2)(1993)166- roding to A point in curves). Sometimes, the subsequent load 176 can exceed the breaking load, such as oB >0A in the cure of [5] M.C. Shaw, D.B. Marshall, M.S. Dadkhah, A.G. Evans, Acta Mater. 4 Al2O3/(Al2O3+Ni)/Ni laminar with five layers and x=2. The (1993)3311-322 reason probably is the metal layers greatly deform under the [6]Z Chen, J.J. Mecholsky, J Mater. Res. 8(1993)2362-2369 working of force(Fig. 7). The improved fracture toughness is 7 J. L. He, W.Z.Li, H D. Li, C H. Liu, Surf. Coat. Technol. 103-104(1998) 76-280. the dominant factor in the improved strength [8] 18 F. Gaudette, S Suresh, A.G. Evans, G. Dehm, M. Ruhle, Acta Mater. 45 (1997)3503-3513 4. Conclusions [91 K.H. Zuo, D.L. Jiang, Q.. Lin, Mater. Lett. 60(2006)1265-1268 [101S.. Pateras, M.C. Shaw, w.J. Clegg, A.C. F Cocks, T.w. Clyne, Proceed- ICCM-19 B C. Whistle Canada. 1995 Aqueous tape casting combined with hot pressing can be [11 T Chartier, D. Merle, J. L Besson, J. Eur. Ceram Soc. 15(1995)101-107 used to fabricate the(Al2O3 +Ni)composite, (Al2O3+ Ni)/Ni [12]GCWei, P.F. Becher,JAm Ceram Soc. 67(1984)571-574 and Al2O3/(AlO3+Ni)/Ni laminated materials. There are no [13] E. Breval, Z. Deng, S. Chiou, C.G. Pantanol, J. Mater. Sci. 27(1992) defects. such as crack. delamination. and distortion and so 1464-1568 on in sintered(AlO3+Ni) osite and laminated materi- [4T Seino, T. Nakajima, S. Ueda, K. Niihara, J Am Ceram Soc. 80(1997) als. The mismatch of thermal expansion coefficient of Ni and [15)S T. Oh, T Sekino, K. Nihara, J. Eur. Ceram Soc. 18(1998) Al2O3 results in the generating the residual radial tensile stress [16]RZ. Chen, W.H. Tuan, J. Eur.Ceram Soc. 19(1999)463-468 nd radial tangential compressive stress surrounding the Al2O3 [17] K H Zuo, D L Jiang,.LLin, Ceram. Int 32(2006)613-616 matrix particles and strengthen the particle boundaries of matrix. [18] R W. Davidge, TJ. Green, J Mater. Sci.3(1968)629-634
300 K.H. Zuo et al. / Materials Science and Engineering A 443 (2007) 296–300 Fig. 7. Optical graphs of laminated materials after measuring fracture strength, indicating the metal layers deform greatly. step-wise load behavior, characterized of non-catastrophic fracture. Unlike the load–displacement cure of usually composite materials, such as Al2O3/Ni laminar with three layers and x = 7, the displacement–load cures of (Al2O3 + Ni)/Ni with three layers and x = 2 and Al2O3/(Al2O3 + Ni)/Ni laminar with five layers and x = 2 arise after the outermost ceramic layer breaking (corroding to A point in curves). Sometimes, the subsequent load can exceed the breaking load, such as σB > σA in the cure of Al2O3/(Al2O3 + Ni)/Ni laminar with five layers and x = 2. The reason probably is the metal layers greatly deform under the working of force (Fig. 7). The improved fracture toughness is the dominant factor in the improved strength [8]. 4. Conclusions Aqueous tape casting combined with hot pressing can be used to fabricate the (Al2O3 + Ni) composite, (Al2O3 + Ni)/Ni and Al2O3/(Al2O3 + Ni)/Ni laminated materials. There are no defects, such as crack, delamination, and distortion and so on in sintered (Al2O3 + Ni) composite and laminated materials. The mismatch of thermal expansion coefficient of Ni and Al2O3 results in the generating the residual radial tensile stress and radial tangential compressive stress surrounding the Al2O3 matrix particles and strengthen the particle boundaries of matrix. Because of the crack deflection by residual stress and Ni particles, and crack bridging by Ni particles, the strength and fracture toughness of (Al2O3 + Ni) composite are higher than those of pure Al2O3. The toughness of (Al2O3 + Ni)/Ni and Al2O3/(Al2O3 + Ni)/Ni laminated materials are higher than not only that of pure Al2O3, but also that of Al2O3/Ni with the same layer number and x, due to the toughen mechanism of laminated structure and composite with the second-phase. The strength and toughness of (Al2O3 + Ni)/Ni with three layers and x = 2 are 417.41 MPa and 12.42 MPa m1/2, which are 1.2 and 3.5 times of pure Al2O3, whose mechanical property of the material is good. The highest toughness of the Al2O3/(Al2O3 + Ni)/Ni laminated material is 16.10 MPa m1/2, which is the 4.6 times of that of pure Al2O3. Acknowledgments This work is supported by the Science and Technology Committee of Shanghai Municipal under the project No. 02DJ14065 and by Chinese Academy of Science under the project No. ICGCX2-SW-602-3. References [1] W.J. Clegg, K. Kendall, N.M. Alford, T.W. Button, J.D. Birchall, Nature (London) 347 (4) (1990) 455–457. [2] W.J. Clegg, Acta Metall. Mater. 40 (11) (1992) 3085–3093. [3] A.J. Phillipps, W.J. Clegg, T.W. Clyne, Acta Metall. Mater. 41 (3) (1993) 805–817. [4] A.J. Phillipps, W.J. Clegg, T.W. Clyne, Composites 24 (2) (1993) 166– 176. [5] M.C. Shaw, D.B. Marshall, M.S. Dadkhah, A.G. Evans, Acta Mater. 41 (1993) 3311–3322. [6] Z. Chen, J.J. Mecholsky, J. Mater. Res. 8 (1993) 2362–2369. [7] J.L. He, W.Z. Li, H.D. Li, C.H. Liu, Surf. Coat. Technol. 103–104 (1998) 276–280. [8] F. Gaudefte, S. Suresh, A.G. Evans, G. Dehm, M. Ruhle, Acta Mater. 45 ¨ (1997) 3503–3513. [9] K.H. Zuo, D.L. Jiang, Q.L. Lin, Mater. Lett. 60 (2006) 1265–1268. [10] S.K. Pateras, M.C. Shaw, W.J. Clegg, A.C.F. Cocks, T.W. Clyne, Proceedings of ICCM-19 B.C. Whistle Canada, 1995. [11] T. Chartier, D. Merle, J.L. Besson, J. Eur. Ceram. Soc. 15 (1995) 101–107. [12] G.C. Wei, P.F. Becher, J. Am. Ceram. Soc. 67 (1984) 571–574. [13] E. Breval, Z. Deng, S. Chiou, C.G. Pantanol, J. Mater. Sci. 27 (1992) 1464–1568. [14] T. Seino, T. Nakajima, S. Ueda, K. Niihara, J. Am. Ceram. Soc. 80 (1997) 1139–1148. [15] S.T. Oh, T. Sekino, K. Niihara, J. Eur. Ceram. Soc. 18 (1998) 31–37. [16] R.Z. Chen, W.H. Tuan, J. Eur. Ceram. Soc. 19 (1999) 463–468. [17] K.H. Zuo, D.L. Jiang, Q.L. Lin, Ceram. Int. 32 (2006) 613–616. [18] R.W. Davidge, T.J. Green, J. Mater. Sci. 3 (1968) 629–634