《复合材料 Composites》课程教学资源（学习资料）第五章陶瓷基复合材料_residual stress in A-Z.pdf_大学文库

Journal of the European Ceramic Society 19(1999)1329-1331 Printed in Great Britain. All rights reserved PII:S0955-2219(98)00428-2 0955-2219/99/S-see front matter Residual stresses in layered ceramic Composites Henryk Tomaszewski* Institute of Electronic Materials Technology, olczynska 133, 01-919 Warsaw, Poland abstract showed that the main mechanism responsible for toughness increase in laminated composites is Laminar composites containing layers of y-TZP or deflection of crack caused by presence of residual Ce-TZP and either A12O3 or a mixture of alumina stresses. Correlation between crack deflection and and zirconia have been fabricated using a sequential distribution of residual stresses found in barrier centrifuging technique of water solutions containing layers of composites was the aim of this work experiments with notched beams of composites showed the significant effect of barrier layer thick 2 Experimental Procedure and composition on crack propagation pai during fracture. Distinct crack deflection was Composites of Y-TZP or Ce-TZP with alumina observed in alumina layers. In the case of layers layers with thicknesses of 10 to 70 um were fabri- made of an oxide mixture, crack deflection was not cated by sequential centrifuging(Model Z382 found independently on layer thickness. The Hermle) of powder suspensions (0.6um ZrO observed changes have been correlated with distribu- +3 4 mol% Y2O3 from Unitec Ceramics, 0-3 um tion of residual stresses in barrier layers created Ce-ZrO2 from Tosoh, 0-29 um Al2O3 from Sumi during cooling of sintered composites from fabrica- tomo). Aqueous slurries containing 5 to 10 wt% of tion temperature. C 1999 Elsevier Science Limited. subsequent powder were prepared by ultrasonicat All rights reserved ing the powders in deionized water at pH 4. Cast samples were dried, additionally isostatically pres- Keywords: crack deflection, thermal expansion, sed at 120 MPa and then sintered at 1600 C. The ZrO,, Al2O3. larger shrinkage of Y-ZrO2 and Ce-ZrO2 than Al2O3 during sintering caused that in some layered position 1 Introduction alumina and zirconia was used instead of a pure AlO3 to minimize this mismatch. The samples Ceramic materials are naturally brittle, so much after sintering were cut and ground and one effort has been directed to improve their toughness surface perpendicular to the layers was polished by various methods. Since the discovery of trans- The sharp notch in the center of the beams was formation toughening in ZrO2 in 1975 a variety of prepared toughened ZrO-based materials have been devel- The tests of controlled crack growth were per oped. A new way of optimization in ceramic sys- formed using a universal testing machine(Model tems strengthened by tetragonal ZrO was found 1446, Zwick) in three-point bending with by Marshall.3 in multilayered ceramic composites. I um min- loading speed and 40 mm bearing dis- A significant toughness increase of Ce-TZP matrix tance. The crack was initiated and slowly grown up with Al,O3 or Al,O3/ZrO, barrier layers was step by step in a controlled way by permanent attributed to the spreading of the transformation loading and removing of the load. The path of the zone along the regions adjacent to the layers. On crack during fracture was registered by SEm using the contrary to Marshall results, reported work a microscope(Model Opton DSM 950) The spatial distribution of residual stresses within the alumina and a mixture of alumina and *Fax:+48-22-8349003: e-mail: tomasz h @sp itme. edu.pl zirconia layer of composites was measured 1329

Residual Stresses in Layered Ceramic Composites Henryk Tomaszewski* Institute of Electronic Materials Technology, WoÂlczynÂska 133, 01-919 Warsaw, Poland Abstract Laminar composites containing layers of Y-TZP or Ce-TZP and either A12O3 or a mixture of alumina and zirconia have been fabricated using a sequential centrifuging technique of water solutions containing suspended particles. Controlled crack growth experiments with notched beams of composites showed the signi®cant eect of barrier layer thickness and composition on crack propagation path during fracture. Distinct crack de¯ection was observed in alumina layers. In the case of layers made of an oxide mixture, crack de¯ection was not found independently on layer thickness. The observed changes have been correlated with distribution of residual stresses in barrier layers created during cooling of sintered composites from fabrication temperature. # 1999 Elsevier Science Limited. All rights reserved Keywords: crack de¯ection, thermal expansion, ZrO2, A12O3. 1 Introduction Ceramic materials are naturally brittle, so much eort has been directed to improve their toughness by various methods. Since the discovery of transformation toughening in ZrO2 in 19751 a variety of toughened ZrO2-based materials have been developed. A new way of optimization in ceramic systems strengthened by tetragonal ZrO2 was found by Marshall2,3 in multilayered ceramic composites. A signi®cant toughness increase of Ce-TZP matrix with Al2O3 or Al2O3/ZrO2 barrier layers was attributed to the spreading of the transformation zone along the regions adjacent to the layers. On the contrary to Marshall results, reported work showed that the main mechanism responsible for toughness increase in laminated composites is de¯ection of crack caused by presence of residual stresses. Correlation between crack de¯ection and distribution of residual stresses found in barrier layers of composites was the aim of this work. 2 Experimental Procedure Composites of Y-TZP or Ce-TZP with alumina layers with thicknesses of 10 to 70m were fabricated by sequential centrifuging (Model Z382, Hermle) of powder suspensions (0.6m ZrO2 +3.4 mol% Y2O3 from Unitec Ceramics, 0.3m Ce-ZrO2 from Tosoh, 0.29m Al2O3 from Sumitomo). Aqueous slurries containing 5 to 10 wt% of subsequent powder were prepared by ultrasonicating the powders in deionized water at pH 4. Cast samples were dried, additionally isostatically pressed at 120 MPa and then sintered at 1600C. The larger shrinkage of Y-ZrO2 and Ce-ZrO2 than A12O3 during sintering caused that in some layered composites the mixed composition of 50 vol% alumina and zirconia was used instead of a pure Al2O3 to minimize this mismatch. The samples after sintering were cut and ground and one surface perpendicular to the layers was polished. The sharp notch in the center of the beams was prepared. The tests of controlled crack growth were performed using a universal testing machine (Model 1446, Zwick) in three-point bending with 1m minÿ1 loading speed and 40 mm bearing distance. The crack was initiated and slowly grown up step by step in a controlled way by permanent loading and removing of the load. The path of the crack during fracture was registered by SEM using a microscope (Model Opton DSM 950). The spatial distribution of residual stresses within the alumina and a mixture of alumina and zirconia layer of composites was measured using Journal of the European Ceramic Society 19 (1999) 1329±1331 # 1999 Elsevier Science Limited Printed in Great Britain. All rights reserved PII: S0955-2219(98)00428-2 0955-2219/99/$ - see front matter 1329 *Fax: +48-22-8349003; e-mail: tomasz_h@sp.itme.edu.pl

1330 H. Tomaszewski piezospectroscopic technique+(spectrometer Dilor biaxial, tensile stresses were expected in the layer X4800) with the greater thermal expansion(zirconia). Pie zospectroscopic measurements showed that the distribution of compressive stresses was different in 3 Results and discussion both types of barrier layers. In the alumina layers compressive stress was not only a function of the Controlled crack growth experiments indicated layer thickness but also of the position across the significant crack deflection in barrier layers of layer(Figs 3 and 4). Maximum of compressive composites dependent on barrier composition but stress was observed at the interface(280 MPa)and not on type of zirconia matrix. It occurred that minimum in the center of alumina layer. The crack deflects only in alumina layers(Figs I and 2). minimum stress was dependent on alumina layer In zirconia layers crack deflects back to its original thickness (Table 1). On the contrary, in ba arrie direction perpendicular to the layers. The degree of crack deflection depends on alumina layer thick ness(Table 1). As it was shown at Figs I and 2 in barrier layers made of an oxide mixture crack pro- agates perpendicularly to the layers without 28 deflection independently on layer thickness Generally crack deflection is related to residual thermal stresses and instantaneous elastic modulus 表属 mismatch effects. In the present case the residual biaxial compressive stress was expected in the layer with lower thermal expansion coefficient(alumina), 普1636 Fig. 2. Crack path during fracture of Ce-TZ/Al2O3 composite with 50 um thick barrier layers made of alumina(bottom, Table 1. Crack deflection angle and compressive stress in minimum in alumina layers of Y-TZP/Al,O3 composite as a function of layer thickness 85l Thickness of Crack deflection Compressive stress alumina laver 22±5 229·2 Fig. 1. Crack path in 60 um thick alumina layer(bottom, 40 62±8 1219 inverted image)and in 45 um thick barrier layers made of an 60 91-6 oxide mixture(top, normal age)of Y-TZP/Al2O3 composite

piezospectroscopic technique4 (spectrometer Dilor X4800). 3 Results and Discussion Controlled crack growth experiments indicated signi®cant crack de¯ection in barrier layers of composites dependent on barrier composition but not on type of zirconia matrix. It occurred that crack de¯ects only in alumina layers (Figs 1 and 2). In zirconia layers crack de¯ects back to its original direction perpendicular to the layers. The degree of crack de¯ection depends on alumina layer thickness (Table 1). As it was shown at Figs 1 and 2 in barrier layers made of an oxide mixture crack propagates perpendicularly to the layers without de¯ection independently on layer thickness. Generally crack de¯ection is related to residual thermal stresses and instantaneous elastic modulus mismatch eects. In the present case the residual biaxial compressive stress was expected in the layer with lower thermal expansion coecient (alumina), biaxial, tensile stresses were expected in the layer with the greater thermal expansion (zirconia). Piezospectroscopic measurements showed that the distribution of compressive stresses was dierent in both types of barrier layers. In the alumina layers compressive stress was not only a function of the layer thickness but also of the position across the layer (Figs 3 and 4). Maximum of compressive stress was observed at the interface (280MPa) and minimum in the center of alumina layer. The minimum stress was dependent on alumina layer thickness (Table 1). On the contrary, in barrier Fig. 1. Crack path in 60m thick alumina layer (bottom, inverted image) and in 45 m thick barrier layers made of an oxide mixture (top, normal age) of Y-TZP/Al2O3 composite. Fig. 2. Crack path during fracture of Ce-TZ/Al2O3 composite with 50m thick barrier layers made of alumina (bottom, inverted image) and an oxide mixture (top, normal image). Table 1. Crack de¯ection angle and compressive stress in minimum in alumina layers of Y-TZP/Al2O3 composite as a function of layer thickness Thickness of alumina layer (m) Crack de¯ection angle () Compressive stress in minimum (MPa) 10 0 266.8 25 225 229.2 40 628 121.9 60 90 91.6 1330 H. Tomaszewski

《复合材料 Composites》课程教学资源（学习资料）第五章 陶瓷基复合材料_residual stress in A-Z

《复合材料 Composites》课程教学资源（学习资料）第五章陶瓷基复合材料_residual stress in A-Z