Availableonlineatwww.sciencedirectcom ScienceDirect E噩≈RS ELSEVIER Joumal of the European Ceramic Society 27(2007)1373-1377 www.elsevier.com/locate/jeurceramsoc Multilayer ceramic composites with high failure resistance Henryk Tomaszewski", Helena Weglarz, Anna Wajler, Marek boniecki Dariusz Kalinski Institute of Electronic Materials Technology, Wolezynska 133, 01-919 Warsaw, Poland Available online 19 May 2006 Since Clegg et al. first fabricated SiC/C multilayer composites in 1990, multilayer ceramics have received much attention because of their improved properties achieved by designing weak interfaces. The weak interface can deflect the crack propagating perpendicularly to the plane of laminates repeatedly during fracture, thus leading to extremely high work-of-fracture. In this work multilayer composites of Al2O3/LaPO4 were prepared ng tape casting technique. Alumina slurry with acrylic latex binder was cast first on a polyester film, dried and then coated by LaPOa interlayer cast on it. The coated green tapes were dried, stacked and laminated. After the removal of the binder, the green body was hot pressed in argon atmosphere at 1280C. A series of experiments were designed and conducted to investigate the influence of geometrical factors on mechanical properties of multilayer composites. Work-of-fracture of layered composites as high as 1100 J/m2 has been found 2006 Elsevier Ltd. All rights reserved Keywords: Layered ceramic composites 1. Introduction In this paper, all-oxide ceramics were fabricated by a low cost, tape casting technique without incorporating expensive Ceramics have many excellent properties that make their use fibers. The material was LaPO4 containing alumina laminate as structural materials very attractive. However, their brittleness A series of experiments were designed to investigate the influ- has prevented their use in structural application to date. The most ence of geometrical factors(thickness of matrix layer and promising candidates for improving ceramic brittleness have interlayer) on crack propagation and mechanical properties of been continuous fiber ceramic composites, which have shown Al2O3/LaPO4 multilayer ceramics high strength and toughness These basic materials include sil- icon carbide or boron nitride layer between fiber and matrix, to 2. Experimental procedure weaken the fiber/matrix interface. without a weak interface. the fiber-reinforced composites demonstrated catastrophic failure Alumina(Taimicron TM-DAR from Taimei Chemicals Co However, the high fabrication cost of these materials and the high Japan)and LaPO4(Strem Chemicals Inc, USA)powders were temperature oxidation of the interlayer and polymer-derived used for fabricating multilayer composites by tape casting tech- fibers remained a technological problems to solve. Ultimate nique. The slurry formulation contained 60 wt% oxide pow materials occurred to be laminate composites, where matrix der, 30 wt% distilled water, 10 wt% acrylic latex(DM765A and interlayer have been exchanged by oxides, - behaving like Clariant, Germany)as a binder and plasticizer and 0.1 wt% dis- carbon and boron nitride in non-oxide systems. A potential oxide persant(Dispex A-40, Allied Colloids Co., Great Britain). Alu interphase is lanthanum phosphate (LaPO4), having a monazite mina slurry was cast first to yield laminae of 50-300 um thick structure, which was proposed by Morgan and Marshall and ness, dried and then coated by LaPO4 interlayer of 10-100 um ttrium phosphate(YPO4), with a xenotime structure evaluated thickness cast on it. The double green tapes were dried, punched by Kuo and Riven. into a rectangle(40 mm x 80 mm), stacked and laminated by uniaxial and isostatic cold pressing. After the removal of the organic additives, the green body was hot pressed in argon atmosphere at 1280C. The hot pressed samples were cut Corresponding author. Tel: +48 228353041x472: fax: +48228349003. and ground to the dimensions of 45 mm x 4 mm x 4 mm or E-mail address: henryk tomaszewski@itme. edu.pl (H. Tomaszewski) 45mm×4mm×2mm 0955-2219/S-see front matter o 2006 Elsevier Ltd. All rights reserved. doi: 10. 1016/j-jeurceramsoc. 2006.04.030
Journal of the European Ceramic Society 27 (2007) 1373–1377 Multilayer ceramic composites with high failure resistance Henryk Tomaszewski ∗, Helena Weglarz, Anna Wajler, ˛ Marek Boniecki, Dariusz Kalinski Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warsaw, Poland Available online 19 May 2006 Abstract Since Clegg et al. first fabricated SiC/C multilayer composites in 1990, multilayer ceramics have received much attention because of their improved properties achieved by designing weak interfaces. The weak interface can deflect the crack propagating perpendicularly to the plane of laminates repeatedly during fracture, thus leading to extremely high work-of-fracture. In this work multilayer composites of Al2O3/LaPO4 were prepared using tape casting technique. Alumina slurry with acrylic latex binder was cast first on a polyester film, dried and then coated by LaPO4 interlayer cast on it. The coated green tapes were dried, stacked and laminated. After the removal of the binder, the green body was hot pressed in argon atmosphere at 1280 ◦C. A series of experiments were designed and conducted to investigate the influence of geometrical factors on mechanical properties of multilayer composites. Work-of-fracture of layered composites as high as 1100 J/m2 has been found. © 2006 Elsevier Ltd. All rights reserved. Keywords: Layered ceramic composites 1. Introduction Ceramics have many excellent properties that make their use as structural materials very attractive. However, their brittleness has prevented their use in structural application to date. The most promising candidates for improving ceramic brittleness have been continuous fiber ceramic composites, which have shown high strength and toughness.1 These basic materials include silicon carbide or boron nitride layer between fiber and matrix, to weaken the fiber/matrix interface. Without a weak interface, the fiber-reinforced composites demonstrated catastrophic failure. However, the high fabrication cost of these materials and the high temperature oxidation of the interlayer and polymer-derived fibers remained a technological problems to solve. Ultimate materials occurred to be laminate composites,2 where matrix and interlayer have been exchanged by oxides,3–5 behaving like carbon and boron nitride in non-oxide systems. A potential oxide interphase is lanthanum phosphate (LaPO4), having a monazite structure, which was proposed by Morgan and Marshall6 and yttrium phosphate (YPO4), with a xenotime structure evaluated by Kuo and Kriven.7 ∗ Corresponding author. Tel.: +48 22 8353041x472; fax: +48 22 834 9003. E-mail address: henryk.tomaszewski@itme.edu.pl (H. Tomaszewski). In this paper, all-oxide ceramics were fabricated by a lowcost, tape casting technique without incorporating expensive fibers. The material was LaPO4 containing alumina laminate. A series of experiments were designed to investigate the influence of geometrical factors (thickness of matrix layer and interlayer) on crack propagation and mechanical properties of Al2O3/LaPO4 multilayer ceramics. 2. Experimental procedure Alumina (Taimicron TM-DAR from Taimei Chemicals Co., Japan) and LaPO4 (Strem Chemicals Inc., USA) powders were used for fabricating multilayer composites by tape casting technique. The slurry formulation contained ∼60 wt% oxide powder, ∼30 wt% distilled water, ∼10 wt% acrylic latex (DM765A, Clariant, Germany) as a binder and plasticizer and∼0.1 wt% dispersant (Dispex A-40, Allied Colloids Co., Great Britain). Alumina slurry was cast first to yield laminae of 50–300 m thickness, dried and then coated by LaPO4 interlayer of 10–100 m thickness cast on it. The double green tapes were dried, punched into a rectangle (40 mm × 80 mm), stacked and laminated by uniaxial and isostatic cold pressing. After the removal of the organic additives, the green body was hot pressed in argon atmosphere at 1280 ◦C. The hot pressed samples were cut and ground to the dimensions of 45 mm × 4 mm × 4 mm or 45 mm × 4 mm × 2 mm. 0955-2219/$ – see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2006.04.030
1374 H Tomaszewski et al. Journal of the European Ceramic Society 27(2007)1373-1377 AlO/LaPO4 WOF=1165 J AlzO3 monolithic, WOF=36 2J/m 188 20 2472 85 Fig. 2. Typical load-displacement curves of Al2O3/LaPO4 multilayer compos- Fig. 1. Typical micrograph showing polished surface of layered composite: ite( matrix layer of 100 um and LaPOa of 20 um)and monolithic Al2O3 prepared Al2O3 layer(dark one)and LaPO4 layer(light one)with thickness of 100 and at the same conditions ALO3/LaPO, WOF=903,8J/m2 The microstructure of composites was observed by scan aPO4 monolithic WOF=4, 7J/m ning electron microscope(SEM) of OPTON DSM 950. Typical micrograph is shown in Fig. I he bending strength of composites was determined on square bars having the dimensions 45 mm x 4 mm x 4 mm per- pendicularly to the layers in three-point bending tests using a universal testing machine(Model 1446, Zwick) with l mm/min loading speed and 35 mm bearing distance For measurement of youngs modulus the beams were thinned to the height of l mm and then the compliance of the samples was recorded during loading tests with 0.1 mm/min loading speed and 40 mm bearing distance. The values of Youngs modulus were determined using the relationship given by Fett and Munz. Displacement, mm he controlled crack growth tests were performed on notched Fig 3. Typical load-displacement curves of Al2O3/LaPO4 multilayer com- bars with one surface perpendicular to the layers polished and posite(matrix layer of 200 um and LapO4 of 20 um) and monolithic LapO4 dimensions 45 mm x 4 mm x 2 mm during three-point bending prepared at the same conditions with 5 um/min loading speed and 40 mm bearing distance. The path of the crack during fracture was registered by optical micro- in Table 1. The load Ns g and 3, are chat of multilayer normal air environments. Regarding that the area under the non-catastrophic fracture. To reveal the detailed nature of the recorded load-deflection curve of the specimen is the sum of the fracture, the flexural test of the laminates for some samples ork used for creating of two new surfaces and the elastic strain was stopped before the bend bar broke and the specimens were energy of the system and sample studied, the work-of-fracture, examined under optical and scanning electron microscopes. As yF, was determined it occurred, the first slope change in the elastic region of the In all cases 10 composite samples has been used to determine load-displacement curve seen at about 35-40N load can be bending strength and work -of-fracture and calculate standard deviation Table 1 Comparison of mechanical properties of monolithic component materials and 3. Results Al2O3 /LaPO4 multilayer composite Material Bending strength(MPa) Work-of-fracture (J/m- As can be seen from Figs. 2 and 3 component materials of Al2O3 /LaPO4 layered composite fracture catastrophically at 432.3±10.2 36.2±3.2 LaPO 030±5.2 4.7±05 loading speed used in controlled crack growth tests. Bending AI203/LaPOa composite 356.3+25.6 1165.1±120.1 strength and work-of-fracture both of these materials are listed
1374 H. Tomaszewski et al. / Journal of the European Ceramic Society 27 (2007) 1373–1377 Fig. 1. Typical micrograph showing polished surface of layered composite: Al2O3 layer (dark one) and LaPO4 layer (light one) with thickness of 100 and 50m, respectively. The microstructure of composites was observed by scanning electron microscope (SEM) of OPTON DSM 950. Typical micrograph is shown in Fig. 1. The bending strength of composites was determined on square bars having the dimensions 45 mm × 4 mm × 4 mm perpendicularly to the layers in three-point bending tests using a universal testing machine (Model 1446, Zwick) with 1 mm/min loading speed and 35 mm bearing distance. For measurement of Young’s modulus the beams were thinned to the height of 1 mm and then the compliance of the samples was recorded during loading tests with 0.1 mm/min loading speed and 40 mm bearing distance. The values of Young’s modulus were determined using the relationship given by Fett and Munz.8 The controlled crack growth tests were performed on notched bars with one surface perpendicular to the layers polished and dimensions 45 mm × 4 mm × 2 mm during three-point bending with 5m/min loading speed and 40 mm bearing distance. The path of the crack during fracture was registered by optical microscope and SEM. All experiments were done at room temperature in normal air environments. Regarding that the area under the recorded load–deflection curve of the specimen is the sum of the work used for creating of two new surfaces and the elastic strain energy of the system and sample studied, the work-of-fracture, γF, was determined.5 In all cases 10 composite samples has been used to determine bending strength and work-of-fracture and calculate standard deviation. 3. Results As can be seen from Figs. 2 and 3 component materials of Al2O3/LaPO4 layered composite fracture catastrophically at loading speed used in controlled crack growth tests. Bending strength and work-of-fracture both of these materials are listed Fig. 2. Typical load–displacement curves of Al2O3/LaPO4 multilayer composite (matrix layer of 100m and LaPO4 of 20m) and monolithic Al2O3 prepared at the same conditions. Fig. 3. Typical load–displacement curves of Al2O3/LaPO4 multilayer composite (matrix layer of 200m and LaPO4 of 20m) and monolithic LaPO4 prepared at the same conditions. in Table 1. The load–displacement responses of multilayer composites, shown in Figs. 2 and 3, are characteristic of the non-catastrophic fracture. To reveal the detailed nature of the fracture, the flexural test of the laminates for some samples was stopped before the bend bar broke and the specimens were examined under optical and scanning electron microscopes. As it occurred, the first slope change in the elastic region of the load–displacement curve seen at about 35–40 N load can be Table 1 Comparison of mechanical properties of monolithic component materials and Al2O3/LaPO4 multilayer composite Material Bending strength (MPa) Work-of-fracture (J/m2) Al2O3 432.3 ± 10.2 36.2 ± 3.2 LaPO4 103.0 ± 5.2 4.7 ± 0.5 Al2O3/LaPO4 composite 356.3 ± 25.6 1165.1 ± 120.1
H. Tomaszewski et al. Journal of the European Ceramic Sociery 27 (2007)1373-1377 1375 1 599 NC89/7 8s°5d Fig. 4. Path of the crack propagating through layered composite for loading stopped at 50N Gust after the first slope change in the elastic region of the lacement curve shown in Fig. 2). related to cracking of the matrix layer(Fig 4). After opening at the bottom of the notch crack propagates through the matrix layer perpendicularly and then deflects in the LapO4 layer running at the interface to the left and right side. Continuous load increase is observed at the load-displacement curve during delamination The delaminated interfaces extend laterally up to some millime tres to the outer loading points, but do not run to the end of the test bar. The laminate delaminates up to the first load drop and dissi- pates the strain energy by creating free surfaces. At this stage, the Al2O3 layer plays an important role. This strong layer supports the applied load, which keeps the delaminated composite from fracturing catastrophically. At the first load drop accumulated strain energy occurs to big and crack propagates perpendic- 100m ularly, running through some pairs of alumina/lanthanum phosphate layers. Close relation between volume of the first load drop, thickness of the matrix layer and amount of matrix layer broken was observed. In the case of matrix layers 100 um Fig. 5. Optical micrograph showing the crack path after the first load drop from thick crack crossed 8-lI pairs of layers(see Fig. 5). Amount the load-displacement curve presented in Fig.2. of layers crossed is dependent on the volume of load at the first load drop and varies from sample tested to sample influencing ing in flaw-tolerant ceramics, more effective than those of crack the final value of work-of-fracture For thicker matrix layers the deflection, crack branching and microcracking, which operate first drop of the load appears at lower load and only two of the in most particulate and laminated composites with strong matrix composite layers break(see Figs. 3 and 6), which can be interface related to lower amount of accumulated strain energy. After the As shown in Table 1, Al2O3/LaPO4 layered composites first load drop, crack stops at matrix/interlayer interface, then demonstrate good mechanical properties. As compared with propagates parallel to the layers leading to the following load monolithic alumina, this oxide laminate has a comparable extend at the load-displacement curve. At the second load drop mechanical strength, but excellent work-of-fracture. To find the only two pairs of layers break independent of matrix layer thick- influence of geometrical factors(thickness of matrix layer and ness(see Figs. 6 and 7). As the cracking/delamination events interlayer) on crack propagation and mechanical properties of continue, the load-displacement curve looks like saw teeth Al2 O3/LaPO4 multilayer ceramics two series of laminates with and a non-brittle fracture response is achieved. This fracture matrix layer thickness or interlayer thickness constant were pre- behaviour is similar to that occurring in fiber-reinforced ceramic pared. As it was observed, delaminating crack always runs at composites having a weak interface. Interfacial debonding and matrix/interlayer interface independent of interlayer thickness delamination are followed by load redistribution among unfrac-(Fig 8). It means that decrease of interlayer thickness keep- tured part and the unbroken fibers. Interfacial delamination as ing Al2O3 layer thickness constant can lead to increase of seen in this study is an important toughening mechanism operat- matrix layer/interlayer pairs amount in composite sample and
H. Tomaszewski et al. / Journal of the European Ceramic Society 27 (2007) 1373–1377 1375 Fig. 4. Path of the crack propagating through layered composite for loading stopped at 50 N (just after the first slope change in the elastic region of the load–displacement curve shown in Fig. 2). related to cracking of the matrix layer (Fig. 4). After opening at the bottom of the notch crack propagates through the matrix layer perpendicularly and then deflects in the LaPO4 layer running at the interface to the left and right side. Continuous load increase is observed at the load–displacement curve during delamination. The delaminated interfaces extend laterally up to some millimetres to the outer loading points, but do not run to the end of the test bar. The laminate delaminates up to the first load drop and dissipates the strain energy by creating free surfaces. At this stage, the Al2O3 layer plays an important role. This strong layer supports the applied load, which keeps the delaminated composite from fracturing catastrophically. At the first load drop accumulated strain energy occurs to big and crack propagates perpendicularly, running through some pairs of alumina/lanthanum phosphate layers. Close relation between volume of the first load drop, thickness of the matrix layer and amount of matrix layer broken was observed. In the case of matrix layers 100 m thick crack crossed 8–11 pairs of layers (see Fig. 5). Amount of layers crossed is dependent on the volume of load at the first load drop and varies from sample tested to sample influencing the final value of work-of-fracture. For thicker matrix layers the first drop of the load appears at lower load and only two of the matrix composite layers break (see Figs. 3 and 6), which can be related to lower amount of accumulated strain energy. After the first load drop, crack stops at matrix/interlayer interface, then propagates parallel to the layers leading to the following load extend at the load–displacement curve. At the second load drop only two pairs of layers break independent of matrix layer thickness (see Figs. 6 and 7). As the cracking/delamination events continue, the load–displacement curve looks like saw teeth and a non-brittle fracture response is achieved. This fracture behaviour is similar to that occurring in fiber-reinforced ceramic composites having a weak interface. Interfacial debonding and delamination are followed by load redistribution among unfractured part and the unbroken fibers. Interfacial delamination as seen in this study is an important toughening mechanism operatFig. 5. Optical micrograph showing the crack path after the first load drop from the load–displacement curve presented in Fig. 2. ing in flaw-tolerant ceramics, more effective than those of crack deflection, crack branching and microcracking, which operate in most particulate and laminated composites with strong interfaces.5 As shown in Table 1, Al2O3/LaPO4 layered composites demonstrate good mechanical properties. As compared with monolithic alumina, this oxide laminate has a comparable mechanical strength, but excellent work-of-fracture. To find the influence of geometrical factors (thickness of matrix layer and interlayer) on crack propagation and mechanical properties of Al2O3/LaPO4 multilayer ceramics two series of laminates with matrix layer thickness or interlayer thickness constant were prepared. As it was observed, delaminating crack always runs at matrix/interlayer interface independent of interlayer thickness (Fig. 8). It means that decrease of interlayer thickness keeping Al2O3 layer thickness constant can lead to increase of matrix layer/interlayer pairs amount in composite sample and
H Tomaszewski et al. Journal of the European Ceramic Society 27(2007)1373-1377 《 80 um Fig. 8. Optical micrograph showing the path of delaminating crack in AlO3 /ApOA multilayer composite with 40 um thick LaPO4 interlayer 200um amount of cracking/delamination events responsible for non- catastrophic fracture. According to this thesis work-of-fracture Fig.6.Optical micrograph showing the crack path responsible for of Al2O3/LapO4 multilayer ceramics shown in Fig 9 strongly load-displacement curve shown in Fig. 3. increases with interlayer thickness decrease. Similar curve of bending strength versus interlayer thickness is investigated from Fig. 10. In multilayer ceramics, bending strength is mainly deter- mined by matrix layers. Their amount increases with decreasing interlayer thickness resulting in a small but increase of compos ite strength. (Fig. 11), when Al2O3 layer thickness decreases at interlayer 1200 100um Fig. 9. Work-of-fracture as a function of LaPO4 interlayer thickness for Fig. 7. Optical micrograph showing the crack path after the second load drop Al2O3/LaPO4 multilayer composite with Al2O3 layer thickness(100 um)con- from the load-displacement curve presented in Fig. 2
1376 H. Tomaszewski et al. / Journal of the European Ceramic Society 27 (2007) 1373–1377 Fig. 6. Optical micrograph showing the crack path responsible for load–displacement curve shown in Fig. 3. Fig. 7. Optical micrograph showing the crack path after the second load drop from the load–displacement curve presented in Fig. 2. Fig. 8. Optical micrograph showing the path of delaminating crack in Al2O3/LaPO4 multilayer composite with 40m thick LaPO4 interlayer. amount of cracking/delamination events responsible for noncatastrophic fracture. According to this thesis work-of-fracture of Al2O3/LaPO4 multilayer ceramics shown in Fig. 9 strongly increases with interlayer thickness decrease. Similar curve of bending strength versus interlayer thickness is investigated from Fig. 10. In multilayer ceramics, bending strength is mainly determined by matrix layers. Their amount increases with decreasing interlayer thickness resulting in a small but increase of composite strength. Similar influence on composite work-of-fracture is observed (Fig. 11), when Al2O3 layer thickness decreases at interlayer Fig. 9. Work-of-fracture as a function of LaPO4 interlayer thickness for Al2O3/LaPO4 multilayer composite with Al2O3 layer thickness (100m) constant.
H. Tomaszewski et al. Journal of the European Ceramic Sociery 27 (2007)1373-1377 thickness constant. Matrix layer thickness decrease increases the amount of crack events that reflects in an increase of fracture energy adsorbed during fracture. According to Fig. 12 bending strength of laminate decreases when matrix 4. Conclusions In this work LaPO4 containing Al2O3 laminates with con- ventional two-layer configuration were fabricated and studied Oxide laminate with high strength and work-of-fracture w 60 70 80 obtained exhibiting extended interfacial delamination. The influ- LaPO4 layer thickness, um ence of geometrical factors( thickness of matrix layer and inter- Fig. 10. Bending strength as a function of LaPO4 interlayer thickness for layer)on mechanical properties of Al2O3/LaPO4 multilayer Al2O3/LaPO4 multilayer composite with Alz O layer thickness(100 um)con- ceramics was found References 1. Evans, A G, Perspective on the development of high-toughness ceramics. J. Am. Ceram Soc,1990.73(2),187-206 2. Clegg, w.J., Kendall, K, Alford, N. McN., J. D. and Birchall J. D, A simple way to make tough ceramics. Nature, 1990, 347, 455- 3. Marshall, D. B. Lange, FF and Ratto. JJ, Enhanced fracture toughness in icrocomposites of Ce-ZrO2 and AlO3..Arm Ceram Soc., 1991 7412),2979-2987 4. Marshall, D. B, Design of high-toughness laminar zirconia composites. Ceran.Bl,1992,71(6,969-973 5. Tomaszewski, H, Weglarz, H, Boniecki, M. barrier layer thickness and composition on 100150200250300350 ered zirconia/alumina composites. J. Mater Sci., 200 16,4165 6. Morgan, P E D and Marshall, D. B. Ceramic composites of monazite and Fig. 11. Work-of-fracture as a function of Al2 O3 matrix layer thickness for alumina. J. Am. Ceram. Soc., 1995, 78(6). 1553-1563 AlO3/LaPO4 multilayer composite with LaPO4 interlayer thickness(20 pm) 7. Kuo, D H and Riven, W.M., Fracture of multilayer oxide composites.Mc 8. Fett, T. and Munz, D, Subcritical crack growth of macrocracks in alu nina with R-curve behaviour. J. A. Ceram. Soc., 1992, 75(4).958- 00350 Al2O3 layer thi Fig. 12. Bending strength as a function of trix layer thickness for AlzO3/LaPO4 multilayer composite with LaPO4 interlayer thickness(20 um)
H. Tomaszewski et al. / Journal of the European Ceramic Society 27 (2007) 1373–1377 1377 Fig. 10. Bending strength as a function of LaPO4 interlayer thickness for Al2O3/LaPO4 multilayer composite with Al2O3 layer thickness (100m) constant. Fig. 11. Work-of-fracture as a function of Al2O3 matrix layer thickness for Al2O3/LaPO4 multilayer composite with LaPO4 interlayer thickness (20m) constant. Fig. 12. Bending strength as a function of Al2O3 matrix layer thickness for Al2O3/LaPO4 multilayer composite with LaPO4 interlayer thickness (20m) constant. thickness constant. Matrix layer thickness decrease increases the amount of cracking/delamination events that reflects in an increase of fracture energy adsorbed during fracture. According to Fig. 12 bending strength of laminate decreases when matrix layer thickness increases. 4. Conclusions In this work LaPO4 containing Al2O3 laminates with conventional two-layer configuration were fabricated and studied. Oxide laminate with high strength and work-of-fracture was obtained exhibiting extended interfacial delamination. The influence of geometrical factors (thickness of matrix layer and interlayer) on mechanical properties of Al2O3/LaPO4 multilayer ceramics was found. References 1. Evans, A. G., Perspective on the development of high-toughness ceramics. J. Am. Ceram. Soc., 1990, 73(2), 187–206. 2. Clegg, W. J., Kendall, K., Alford, N. McN., Button, J. D. and Birchall, J. D., A simple way to make tough ceramics. Nature, 1990, 347, 455– 457. 3. Marshall, D. B., Lange, F. F. and Ratto, J. J., Enhanced fracture toughness in layered microcomposites of Ce–ZrO2 and Al2O3. J. Am. Ceram. Soc., 1991, 74(12), 2979–2987. 4. Marshall, D. B., Design of high-toughness laminar zirconia composites. Ceram. Bull., 1992, 71(6), 969–973. 5. Tomaszewski, H., Weglarz, H., Boniecki, M. and Re ˛ cko, W., Effect of ´ barrier layer thickness and composition on fracture toughness of layered zirconia/alumina composites. J. Mater. Sci., 2000, 35(16), 4165– 4176. 6. Morgan, P. E. D. and Marshall, D. B., Ceramic composites of monazite and alumina. J. Am. Ceram. Soc., 1995, 78(6), 1553–1563. 7. Kuo, D. H. and Kriven, W. M., Fracture of multilayer oxide composites. Mater. Sci. Eng. A, 1998, 241, 241–250. 8. Fett, T. and Munz, D., Subcritical crack growth of macrocracks in alumina with R-curve behaviour. J. Am. Ceram. Soc., 1992, 75(4), 958– 963.
