SCIENCE DIRECT S materials letters 要 ELSEVIER Materials Letters 60(2006)1265-1268 www.elsevier.com/locate/matlet Mechanical properties of Al2O3/Ni laminated composites Kai Hui zuo, Dong Liang Jiang, Qing Ling Lin Received 20 July 2005; accepted 5 November 2005 Available online 28 November 2005 Abstract Al,O /Ni laminated composites were prepared by aqueous tape casting and hot pressing with intent to study mechanical properties including the fracture strength and toughness. The residual stress was evaluated and proved. The relations of mechanical properties with the thermal residual stress, the ductility of metal layers and the layer thickness ratio were studied, respectively. It was found that the toughness and work of fracture of Al2O3/Ni laminar reached to 12.56 MPa m"and 12450 J m, which are 3.6 and 478.8 times that of pure Al2O3 o 2005 Elsevier B V. All rights reserved. Keywords: Multilayer structure: Mechanical properties; Thermal residual stress 1. Introduction Shanghai Jiuling Smelting Co, LTD, China) were used as starting materials. The thickness of green tapes was 200-500 In the past decade, layered ceramic composites have been um Al2O3/Ni symmetrical laminated composites(odd number studied extensively [1-4] for its advantage which is insensitiv- of layers)were fabricated by periodically stacking layers of ity to defects. Ceramic/metal composite is an important class of AlO3 and Ni(Fig. 1). Each layer was stacked with some composite materials that can be used in applications ranging Al2O3 or Ni green films. Subsequently, organic additives were from integrated circuits to aircraft engine components. Experi- removed at 800C for 2 h in vacuum drying oven. Then Al2O3/ ments have shown ceramic/metal multilayer composites have Ni laminate was sintered through hot pressing at 25 MPa, under much higher toughness and strength than monolithic ceramics an argon atmosphere at 1400C for 1 h A parameter of the layer thickness ratio x was used (r=h In the present study, tape casting and hot pressing were used hm, where he and hm are the thicknesses of ceramic and metal to Al2O3/Ni laminated materials. The AlO3/Ni material was an layers, respectively). Samples L0302, L1515 and L2930 old material system but the dependence of mechanical proper- denoted that the total amount of layer was 3, 15 and 29, and ties(fracture strength and toughness)on the thickness ratio of x=2, 15 and 30, respectively. Pure Al O3 material was stacked ceramic to metal layer and the amount of layers was a new only with AlO3 green film int. The other influent factors of mechanical properties, such as the thermal residual stress and the ductility of metal layers, were characterized 2. Experiment g of Al2O3 and Ni was used to een tapes. Al2O3(d5o=0.6 um, Shanghai Wusong Fe Factory, China) and Ni electrolytic powders (dso=26 s Corresponding author. Tel +86 21 5241 2606; fax: +86 21 5241 3903 E-mail address: dujiang@sunm shchc ac cn(D L Jiang). Fig 1 Schematic illustration of the Al,O /Ni laminated material. 0167-577X/S- see front matter o 2005 Elsevier B V. All rights reserved. doi:10.1016/ malet2005.11010
Mechanical properties of Al2O3/Ni laminated composites Kai Hui Zuo, Dong Liang Jiang ⁎, Qing Ling Lin The State Key Lab of High Performance Ceramics and Superfine Structure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, PR China Received 20 July 2005; accepted 5 November 2005 Available online 28 November 2005 Abstract Al2O3/Ni laminated composites were prepared by aqueous tape casting and hot pressing with intent to study mechanical properties including the fracture strength and toughness. The residual stress was evaluated and proved. The relations of mechanical properties with the thermal residual stress, the ductility of metal layers and the layer thickness ratio were studied, respectively. It was found that the toughness and work of fracture of Al2O3/Ni laminar reached to 12.56 MPa m1/2 and 12 450 J m−2 , which are 3.6 and 478.8 times that of pure Al2O3. © 2005 Elsevier B.V. All rights reserved. Keywords: Multilayer structure; Mechanical properties; Thermal residual stress 1. Introduction In the past decade, layered ceramic composites have been studied extensively [1–4] for its advantage which is insensitivity to defects. Ceramic/metal composite is an important class of composite materials that can be used in applications ranging from integrated circuits to aircraft engine components. Experiments have shown ceramic/metal multilayer composites have much higher toughness and strength than monolithic ceramics [5–8]. In the present study, tape casting and hot pressing were used to Al2O3/Ni laminated materials. The Al2O3/Ni material was an old material system but the dependence of mechanical properties (fracture strength and toughness) on the thickness ratio of ceramic to metal layer and the amount of layers was a new point. The other influent factors of mechanical properties, such as the thermal residual stress and the ductility of metal layers, were characterized. 2. Experiment Aqueous tape casting of Al2O3 and Ni was used to prepare green tapes. Al2O3(d50= 0.6 μm, Shanghai Wusong Fertilizer Factory, China) and Ni electrolytic powders (d50= 26.5 μm, Shanghai Jiuling Smelting Co., LTD, China) were used as starting materials. The thickness of green tapes was 200–500 μm. Al2O3/Ni symmetrical laminated composites (odd number of layers) were fabricated by periodically stacking layers of Al2O3 and Ni (Fig. 1). Each layer was stacked with some Al2O3 or Ni green films. Subsequently, organic additives were removed at 800 °C for 2 h in vacuum drying oven. Then Al2O3/ Ni laminate was sintered through hot pressing at 25 MPa, under an argon atmosphere at 1400 °C for 1 h. A parameter of the layer thickness ratio x was used (x=hc/ hm, where hc and hm are the thicknesses of ceramic and metal layers, respectively). Samples L0302, L1515 and L2930 denoted that the total amount of layer was 3, 15 and 29, and x= 2, 15 and 30, respectively. Pure Al2O3 material was stacked only with Al2O3 green films. Materials Letters 60 (2006) 1265–1268 www.elsevier.com/locate/matlet ⁎ Corresponding author. Tel.: +86 21 5241 2606; fax: +86 21 5241 3903. E-mail address: dljiang@sunm.shchc.ac.cn (D.L. Jiang). Fig. 1. Schematic illustration of the Al2O3/Ni laminated material. 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.11.010
K H. Zuo et al./Materials Letters 60(2006)1265-1268 (a) -D-3 layers (b) sing identation techniqu caculated using formula(1) △-29 layers 8.0X10 200 20x108 20 X=hc/hm Fig. 2. Residual compressive stress in ceramic layers in AL O, /Ni composites with different n(a) calculated according to formula(1), and(b) measured using formula Three-point bending strength was determined at room tem-84x 10 and 13.2 x10K for a, and a,, and 0.26 and 0.31 perature and a crosshead speed of 0.5 mm min(Instron-1195, for vI and v2, the residual compressive stress in ceramic layers with SA). The toughness was achieved by the single-edge notched different n calculated according to formula(1)is shown in Fig. 2(a) beam test with a crosshead speed of 0.05 mm min-1. Radial Results indicate that the compressive stress increases when the r cracks were generated under a 5 kg indentation load for 10s decreases. In addition, composites with 15 and 29 layers have higher (Akaslll, Instron, USA), in order to study the crack propagation compressive stress than that in sandwich composites. For materials with surface compressive stresses (o), o car profiles and the residual stress measured using another method [1 3. Results and discussion Ke 3. 1. Evaluation of residual stress in Al203//i laminates where Ke and Ke is the toughness of the material without su residual stress and the material with surface residual stress determined There is the residual hydrostatic tension stress in Ni layers and the using the indentation technique. a and c is the local residual stress and residual compressing stress in AL2O, layers for the mismatch of ther- the radius of a half-penny crack. Fig. 2(b)is the data achieved using (8.4x 10K). By means of simplifying the actual material system [11], the data of Fig. 2(b)is discrete. However, the mean value of a is and assuming that the residual stress is in plane stress state and the close to o' and the change tendency of o is the same with that ofal material only occurs the elastic strain, T. Chartier proposed a simple The compressive stress, which has been confirmed by the two inde- formula of the residual compressive stress(o")which is as follows [9): pendent methods, is of great benefit to increase the mechanical prop- d1= nE1E2d2(x2-22)△ erties, which will be discussed in following n(1-v1)E2d+(n+1)(1-2)E1d1 The residual stress also can be observed from the radial cracks generated from the Vickers indentation(Fig. 3). Cracks vertical to the where E1, E2, a1, 02, v1, v2, d, and d2 are the young modulus, thermal lamination orientation bend to the interface, which is found in places xpansion coefficient, Poisson's ratio and layer thickness of ceramic near the interfaces of samples with lower x, such as L0302(Fig 3(b)). and metal, respectively. AT and n are the difference temperature These cracks can be called ring-like cracks, which cannot be found in between the actual and the joining temperature and the amount of pure Al2O3(Fig. 3(a), places far from the interface of Al2O3/Ni composite layers. Using 400 GPa and 210 GPa for E1 and E2, materials and samples with x>10(Fig 3(c). Cracks propagate parallel Fig 3. Optical micrograph of an indentation crack in samples: (a) pure Al203, (b)L0302 and(c)L0315
Three-point bending strength was determined at room temperature and a crosshead speed of 0.5 mm min−1 (Instron-1195, USA). The toughness was achieved by the single-edge notched beam test with a crosshead speed of 0.05 mm min−1 . Radial cracks were generated under a 5 kg indentation load for 10 s (AkasIII, Instron, USA), in order to study the crack propagation profiles and the residual stress. 3. Results and discussion 3.1. Evaluation of residual stress in Al2O3/Ni laminates There is the residual hydrostatic tension stress in Ni layers and the residual compressing stress in Al2O3 layers for the mismatch of thermal expansion coefficient of Ni (13.2 × 10−6 K−1 ) and Al2O3 (8.4 × 10−6 K−1 ). By means of simplifying the actual material system and assuming that the residual stress is in plane stress state and the material only occurs the elastic strain, T. Chartier proposed a simple formula of the residual compressive stress (σ1 ) which is as follows [9]: r1 ¼ nE1E2d2ða2−a2ÞDT nð1−m1ÞE2d2 þ ðn þ 1Þð1−m2ÞE1d1 ð1Þ where E1, E2, α1, α2, ν1, ν2, d1 and d2 are the young modulus, thermal expansion coefficient, Poisson's ratio and layer thickness of ceramic and metal, respectively. ΔT and n are the difference temperature between the actual and the joining temperature and the amount of composite layers. Using 400 GPa and 210 GPa for E1 and E2, 8.4 × 10−6 K−1 and 13.2 × 10−6 K−1 for α1 and α2, and 0.26 and 0.31 for ν1 and ν2, the residual compressive stress in ceramic layers with different n calculated according to formula (1) is shown in Fig. 2(a). Results indicate that the compressive stress increases when the x decreases. In addition, composites with 15 and 29 layers have higher compressive stress than that in sandwich composites. For materials with surface compressive stresses (σ), σ can be measured using another method [10]: Kc ¼ K0 c −2r ffiffiffiffiffiffiffi c=p p ð2Þ where Kc 0 and Kc is the toughness of the material without surface residual stress and the material with surface residual stress determined using the indentation technique. σ and c is the local residual stress and the radius of a half-penny crack. Fig. 2(b) is the data achieved using formula (2). Because the residual stress is different in different ranges [11], the data of Fig. 2(b) is discrete. However, the mean value of σ is close to σ1 and the change tendency of σ is the same with that of σ1 . The compressive stress, which has been confirmed by the two independent methods, is of great benefit to increase the mechanical properties, which will be discussed in following. The residual stress also can be observed from the radial cracks generated from the Vickers indentation (Fig. 3). Cracks vertical to the lamination orientation bend to the interface, which is found in places near the interfaces of samples with lower x, such as L0302 (Fig. 3(b)). These cracks can be called ring-like cracks, which cannot be found in pure Al2O3 (Fig. 3(a)), places far from the interface of Al2O3/Ni materials and samples with xN10 (Fig. 3(c)). Cracks propagate parallel Fig. 2. Residual compressive stress in ceramic layers in Al2O3/Ni composites with different n (a) calculated according to formula (1), and (b) measured using formula (2). Fig. 3. Optical micrograph of an indentation crack in samples: (a) pure Al2O3, (b) L0302 and (c) L0315. 1266 K.H. Zuo et al. / Materials Letters 60 (2006) 1265–1268
K H. Zuo et al./Materials Letters 60(2006)1265-1268 1267 -o-3 layers 3 Δ-29 layers 乏E 300 E 51015 203040 X=hc/hm Fig. 4. Fracture strength, toughness and work of fracture of Al2O / Ni laminates with different layers versus the layer thickness ratio of the ceramic thickness to the metal thickness to the compression axis and normal to the tension axis [12] pure laminated AlO3, respectively. The toughness of all samples is forms the ring-like cracks. Ring-like cracks also confirm that improved in comparison with pure laminar Al2O3. Results indicate that exists the residual stress in Al2O3/Ni composites the flexure strength reaches the maximum before falling, and that the toughness and work of fracture decreases with x increasing. The high- 3. 2. Mechanical properties of composites with different layer thickness est strength of materials with 29 layers is 439.8x 18.1 MPa(L2907 The toughness and work of fracture of L2902 is 12.56 MPa m and 12450 m respectively The mechanical properties of Al2O3/Ni laminates with different The properties of AlO,/Ni laminates with different x are influ- amount of layers are demonstrated in Fig. 4. The dash dot lines enced by the residual stress and the ductility of metal. The residual represent the fracture strength, toughness and work of fracture of stress is the key factor affecting the properties of laminar with higherx 80 (c) 300 8200 0000.040.080.120.160.20 Di cement Displacement /mm Displacement/mm 0.040.080.12 0000.040.080.12 Displacement/mm Fig. 5. Load-displacement curves measure for flexure strength: (a) low carbon steel, (b)L0302, (c)L0306,(d) L0315 and(e) pure Al2O3
to the compression axis and normal to the tension axis [12], which forms the ring-like cracks. Ring-like cracks also confirm that there exists the residual stress in Al2O3/Ni composites. 3.2. Mechanical properties of composites with different layer thickness ratio The mechanical properties of Al2O3/Ni laminates with different amount of layers are demonstrated in Fig. 4. The dash dot lines represent the fracture strength, toughness and work of fracture of pure laminated Al2O3, respectively. The toughness of all samples is improved in comparison with pure laminar Al2O3. Results indicate that the flexure strength reaches the maximum before falling, and that the toughness and work of fracture decreases with x increasing. The highest strength of materials with 29 layers is 439.8 × 18.1 MPa (L2907). The toughness and work of fracture of L2902 is 12.56 MPa m1/2 and 12 450 J m−2 , respectively. The properties of Al2O3/Ni laminates with different x are influenced by the residual stress and the ductility of metal. The residual stress is the key factor affecting the properties of laminar with higher x. Fig. 4. Fracture strength, toughness and work of fracture of Al2O3/Ni laminates with different layers versus the layer thickness ratio of the ceramic thickness to the metal thickness. Fig. 5. Load–displacement curves measure for flexure strength: (a) low carbon steel, (b) L0302, (c) L0306, (d) L0315 and (e) pure Al2O3. K.H. Zuo et al. / Materials Letters 60 (2006) 1265–1268 1267
1268 K H. Zuo et al./Materials Letters 60(2006)1265-1268 When the residual stress is small, it cannot induce cracks, but can both confirm that the residual stress lies in Al2O3/Ni laminar deflect the propagating cracks, for cracks propagate parallel to the composites, and that the compressive stress increases when the ompression axis and normal to the tension axis. These can improve thickness ratio decreases. The residual stress causing cracks the strength and toughness of materials for the energy absorbing deflect is the key factor affecting the properties of laminar mechanism. When the residual stress is high enough. it will weaken with higher x. The character of laminar with lower x is gov yielded ahead of macrocracks (13). These also can improve the tough. emed by the ductility of the nickel, which greatly increases the ness for the strain energy dissipating mechanism accompanied by toughness and the work of fracture by deflecting crack, dela- reduction of strength. So the strength, toughness and work of fracture minating and creating new fracture. The toughness and work of all decrease with x increasing when the thickness ratio is higher than 7. fracture of Al203/Ni laminated composites can reach to 12.56 Fig 5 is the load-displacement curve of low carbon steel(Fig. 5 MPa m and 12450 J,, which is the 3.6 and 478.8times (a), pure Al2O3(Fig. 5(e), and Al2O3/Ni laminates(Fig. 5(b-d). The that of pure Al2O pure Al2O3 laminate exhibited a typical brittleness fracture behavior. Laminates, such as L0315, also display catastrophic fractures. How- Acknowledgments ever, with thicker Ni layer, the load-displacement curves change into the step-wise load, characterized of the non-catastrophic fracture (L0302 and L0306). The relationship of displacement and load This work is supported by the Science and Technolo Fig. 5(b)is very similar to that of metals, such as the low carbon ommittee of Shanghai Municipal under the project No steel(Fig. 5(a).It can be proposed that the characteristics of laminar 02DJ14065 and by Chinese Academy of Science under the with lower r are governed by the ductility of the nickel. When cracks project no. ICGCX2-SW-602-3 arise in Al2O3 layer, the Ni layer will yield plasticity. This will cause the crack deflection along the interface and interface delaminations. References Energy dissipation caused by all of the ductile bridging, interface delamination and new fracture surfaces yielding in the ceramic layer [0W.J.Clegg,KKendall,NM.Alford,TWBotton,JD.Birchall,Nature provide large increases in the toughness and work of fracture of (Lond.)347(1990)455 laminates. But the metal layers also cause the lower strength of the [2] C.H. Yeh, M H Hon, Ceram. Inter. 23(1997)361-366 laminar for the ductility of metal. [3]AJ. Sanchez-Herencia, C. Pascual, J. He, F.F. Lange, J. Am. Ceram. Soc. Fig. 4 also shows that the strength of multi-layer composites is higher than that of sandwich composites, and the toughness and work 4GJ. Zhang, X.M. Yue, T. Watanabe, J. Eur. Ceram. Soc. 19(1999) of fracture of multi-layers are closer than those of sandwich compo- 2111-2116 sites. These results are in good agreement with the results of formula 5]ZChen, J.J. Mecholskym, J. Am. Ceram Soc. 76(1993)1258-1264 6J. L. He, W.Z.Li, H.D. Li, C H Liu, Surf. Coat. Technol (1998)276-280 () The toughness of the sandwich is higher than that of the multi- (73 M.C. Shaw, D.B. Marshall, M.S. Dadkhah, A.G. Evans, Acta Mater. 41 layer. The reason is that the metal layer thickness of sandwich com- (1993)3311-3322 posite is thicker than that of the multi-layer when composites have the [8]F.Gaudefte, SSuresh, A.G. Evans, GDehm, M Ruhle, Acta Mater.4: same height and the same thickness ratio (1997)3503-3513 9 T Chartier, D. Merle, J. L Besson, J. Eur. Ceram Soc. 15(1995)101-107. 4. Conclusions 10) I.K. Yasuro, V.V. Anilv, J Mater. Sci. 19(1984)2233-2238 [11 A. Tomohiko, S. Tohru, N. Tadacihka, K. Takafumi, N. Koichi, Mater. Lett57(2003)3057-3062 The mechanical properties of Al2 O3/Ni laminar composites [2)GCWei,PFBecher, JAmCeram Soc.67(1984)571-574 closely connect with the thermal residual stress, ductility of [13]J.Zhang, R Huang, H Gu, D Jiang,.Lin, ZHuang,Scr.Mater.52 metal and the thickness ratio. Calculation and measurement (2005)381-385
When the residual stress is small, it cannot induce cracks, but can deflect the propagating cracks, for cracks propagate parallel to the compression axis and normal to the tension axis. These can improve the strength and toughness of materials for the energy absorbing mechanism. When the residual stress is high enough, it will weaken the interface between Ni and Al2O3 grains, leading to microcracks yielded ahead of macrocracks [13]. These also can improve the toughness for the strain energy dissipating mechanism accompanied by reduction of strength. So the strength, toughness and work of fracture all decrease with x increasing when the thickness ratio is higher than 7. Fig. 5 is the load–displacement curve of low carbon steel (Fig. 5 (a)), pure Al2O3 (Fig. 5(e)), and Al2O3/Ni laminates (Fig. 5(b–d)). The pure Al2O3 laminate exhibited a typical brittleness fracture behavior. Laminates, such as L0315, also display catastrophic fractures. However, with thicker Ni layer, the load–displacement curves change into the step-wise load, characterized of the non-catastrophic fracture (L0302 and L0306). The relationship of displacement and load in Fig. 5(b) is very similar to that of metals, such as the low carbon steel (Fig. 5(a)). It can be proposed that the characteristics of laminar with lower x are governed by the ductility of the nickel. When cracks arise in Al2O3 layer, the Ni layer will yield plasticity. This will cause the crack deflection along the interface and interface delaminations. Energy dissipation caused by all of the ductile bridging, interface delamination and new fracture surfaces yielding in the ceramic layer provide large increases in the toughness and work of fracture of laminates. But the metal layers also cause the lower strength of the laminar for the ductility of metal. Fig. 4 also shows that the strength of multi-layer composites is higher than that of sandwich composites, and the toughness and work of fracture of multi-layers are closer than those of sandwich composites. These results are in good agreement with the results of formula (1). The toughness of the sandwich is higher than that of the multilayer. The reason is that the metal layer thickness of sandwich composite is thicker than that of the multi-layer when composites have the same height and the same thickness ratio. 4. Conclusions The mechanical properties of Al2O3/Ni laminar composites closely connect with the thermal residual stress, ductility of metal and the thickness ratio. Calculation and measurement both confirm that the residual stress lies in Al2O3/Ni laminar composites, and that the compressive stress increases when the thickness ratio decreases. The residual stress causing cracks deflect is the key factor affecting the properties of laminar with higher x. The character of laminar with lower x is governed by the ductility of the nickel, which greatly increases the toughness and the work of fracture by deflecting crack, delaminating and creating new fracture. The toughness and work of fracture of Al2O3/Ni laminated composites can reach to 12.56 MPa m1/2 and 12 450 J m−2 , which is the 3.6 and 478.8 times 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. Botton, J.D. Birchall, Nature (Lond.) 347 (1990) 455. [2] C.H. Yeh, M.H. Hon, Ceram. Inter. 23 (1997) 361–366. [3] A.J. Sanchez-Herencia, C. Pascual, J. He, F.F. Lange, J. Am. Ceram. Soc. 82 (1999) 1512–1518. [4] G.J. Zhang, X.M. Yue, T. Watanabe, J. Eur. Ceram. Soc. 19 (1999) 2111–2116. [5] Z. Chen, J.J. Mecholskym, J. Am. Ceram. Soc. 76 (1993) 1258–1264. [6] J.L. He, W.Z. Li, H.D. Li, C.H. Liu, Surf. Coat. Technol. (1998) 276–280. [7] M.C. Shaw, D.B. Marshall, M.S. Dadkhah, A.G. Evans, Acta Mater. 41 (1993) 3311–3322. [8] F. Gaudefte, S. Suresh, A.G. Evans, G. Dehm, M. Rühle, Acta Mater. 45 (1997) 3503–3513. [9] T. Chartier, D. Merle, J.L. Besson, J. Eur. Ceram. Soc. 15 (1995) 101–107. [10] I.K. Yasuro, V.V. Anilv, J. Mater. Sci. 19 (1984) 2233–2238. [11] A. Tomohiko, S. Tohru, N. Tadacihka, K. Takafumi, N. Koichi, Mater. Lett. 57 (2003) 3057–3062. [12] G.C. Wei, P.F. Becher, J Am. Ceram. Soc. 67 (1984) 571–574. [13] J. Zhang, R. Huang, H. Gu, D. Jiang, Q. Lin, Z. Huang, Scr. Mater. 52 (2005) 381–385. 1268 K.H. Zuo et al. / Materials Letters 60 (2006) 1265–1268
