《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_Fracture behavior of laminated SiC composites.pdf

CERAMICS INTERNATIONAL SEVIER Ceramics International 30(2004)697-703 www.elsevier.com/locate/ceramint Fracture behavior of laminated SiC composites J.X. Zhang, D L. Jiang Sh.Y. Qin, Zh. R. Huang te Key Laboratory of High Performance Ceramics and Superfine Structure hai Institute of Ceramics hinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, China Received 25 May 2003: received in revised form 19 June 2003; accepted 25 July 2003 Available online 17 March 2004 Abstract Experimental investigation of the fexural properties of SiC/C laminates had been conducted. Effect of the interfacial thickness and compo- sition on the mechanical properties of SiC laminates was characterized. The diffusion of elements from adjacent Sic layers in the carbon-based interfacial layers was studied. Accordingly, the optimal thickness and composition of interfacial layers were determined experimentally o2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved eywords: B. Composites, C. Mechanical properties; C. Fracture; D SiC 1. Introduction The individual layers of laminates with weak interface are usually fabricated by extrusion [5,6, 8, 211, slip casting[19, Active research and development have been conducted electrophoretic deposition [22], non-aqueous tape casting to seek the application of ceramics as structural com- [10, 12, 14, 15, 17, 18, 20] and laminated object manufacturing ponents, however, the lack of damage tolerance abil 231, no paper had ever reported the using of aqueous tape has been a critical problem. It was reported that casting process. As far as we know, the interface layer of continuous-fiber-reinforced ceramic composites(CFCC) laminates are prepared by coating [5,6, 8, 10, 121, spraying are the most promising candidates and have shown a [21], electrophoretic deposition [22], screening [14]and tape non-brittle response [l], but the fabrication of these ad- casting [12, 15, 17, 18] vanced structural materials for high temperature applica- Understanding the fracture behavior of multilayered com- tions is time-consuming and expensive. The concept of posites requires the study of interface crack propagation laminated composite for improved performance of brittle mechanism[24-29]. Phillipps et al. [7, 301, Folsom [31, 32], materials is well established [2]. Such structure is found in and others proposed models of the fracture behavior of ce- many biological hard tissues, such as mollusk shell B3, 4] ramic laminates in bending test. The reliability and fric- and teeth. Clegg and co-workers [5-8] have produced lam- tional energy dissipation in laminates were also investigated inated Sic with graphite interface layers by rolling the [33-35 dough like powder mixture into sheets, coating the sheets Phillipps et al. proposed that the specimen size, in with graphite followed by laminating and sintering. These cluding the beam length, the interfacial toughness, the multilayer SiC composites showed stepped stress-strain lamina thickness will play important roles on the appar- behavior with the apparent toughness and work of fracture ent toughness, work of fracture of laminated composites as 15 MPam/ and 4625 Jm-, respectively. Multilayered [8]. In the present paper, SiC/C laminated composites ceramic materials with weak inter face have been evaluated were prepared through aqueous tape casting and lami- in other ceramic systems, such as Sic/Sic 191, Si]N4/Bn nation process. The properties of the thin C-SiC inter 10-15] or Al2O3/LaPO4 [16], etc. Recently, it was shown facial layers were adjusted by varying the composition that laminated composites without weak interfaces also of the C through the addition of SiC. Influence of the exhibited damage-tolerant behavior [9, 17-201 composition and thickness of interfacial layers on the me- chanical properties of Sic multilayers was studied. The s Corresponding author. microstructure and fracture behavior were investigated E-mailaddress:jxzh@yahoo.com(D.L.Jiang). 0272-8842/$30.00 0 2004 Elsevier Ltd and Techna Group S r l. All rights reserved doi:10.1016/ ceramist2003.07.016

Ceramics International 30 (2004) 697–703 Fracture behavior of laminated SiC composites J.X. Zhang, D.L. Jiang∗, Sh.Y. Qin, Zh.R. Huang The State Key Laboratory of High Performance Ceramics and Superfine Structure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, China Received 25 May 2003; received in revised form 19 June 2003; accepted 25 July 2003 Available online 17 March 2004 Abstract Experimental investigation of the flexural properties of SiC/C laminates had been conducted. Effect of the interfacial thickness and composition on the mechanical properties of SiC laminates was characterized. The diffusion of elements from adjacent SiC layers in the carbon-based interfacial layers was studied. Accordingly, the optimal thickness and composition of interfacial layers were determined experimentally. © 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: B. Composites; C. Mechanical properties; C. Fracture; D. SiC 1. Introduction Active research and development have been conducted to seek the application of ceramics as structural components; however, the lack of damage tolerance ability has been a critical problem. It was reported that continuous-fiber-reinforced ceramic composites (CFCC) are the most promising candidates and have shown a non-brittle response [1], but the fabrication of these advanced structural materials for high temperature applications is time-consuming and expensive. The concept of laminated composite for improved performance of brittle materials is well established [2]. Such structure is found in many biological hard tissues, such as mollusk shell [3,4] and teeth. Clegg and co-workers [5–8] have produced laminated SiC with graphite interface layers by rolling the dough like powder mixture into sheets, coating the sheets with graphite followed by laminating and sintering. These multilayer SiC composites showed stepped stress–strain behavior with the apparent toughness and work of fracture as 15 MPa m1/2 and 4625 J m−2, respectively. Multilayered ceramic materials with weak interface have been evaluated in other ceramic systems, such as SiC/SiC [9], Si3N4/BN [10–15] or Al2O3/LaPO4 [16], etc. Recently, it was shown that laminated composites without weak interfaces also exhibited damage-tolerant behavior [9,17–20]. ∗ Corresponding author. E-mail address: jx zh@yahoo.com (D.L. Jiang). The individual layers of laminates with weak interface are usually fabricated by extrusion [5,6,8,21], slip casting [19], electrophoretic deposition [22], non-aqueous tape casting [10,12,14,15,17,18,20] and laminated object manufacturing [23], no paper had ever reported the using of aqueous tape casting process. As far as we know, the interface layer of laminates are prepared by coating [5,6,8,10,12], spraying [21], electrophoretic deposition [22], screening [14] and tape casting [12,15,17,18]. Understanding the fracture behavior of multilayered composites requires the study of interface crack propagation mechanism [24–29]. Phillipps et al. [7,30], Folsom [31,32], and others proposed models of the fracture behavior of ceramic laminates in bending test. The reliability and frictional energy dissipation in laminates were also investigated [33–35]. Phillipps et al. proposed that the specimen size, including the beam length, the interfacial toughness, the lamina thickness will play important roles on the apparent toughness, work of fracture of laminated composites [8]. In the present paper, SiC/C laminated composites were prepared through aqueous tape casting and lamination process. The properties of the thin C–SiC interfacial layers were adjusted by varying the composition of the C through the addition of SiC. Influence of the composition and thickness of interfacial layers on the mechanical properties of SiC multilayers was studied. The microstructure and fracture behavior were investigated too. 0272-8842/$30.00 © 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2003.07.016

J.x. Zhang et al. /Ceramics International 30(2004)697-703 699 als and Y203(2.85 wt %)and Al203(2.15%)as sintering (SENB) method on test bars of 4 mm high, 3 mm wide and additives. Details concerning the aqueous tape casting pro- 36 mm long by a three-point bend using a span of 30mm cess could be obtained from previous published papers and a cross head speed of 0.05 mm-min. A straight notch [36, 37]. The thickness of the Sic green tapes was adjusted with fine diamond saw was introduced with a depth at about to -150 um To introduce weak interface between SiC lay- 2 mm. Work of fracture was obtained by dividing the area un ers, thin C-SiC sheets were also prepared by tape casting der the load-displacement curve by twice the cross-section process using doctor blade equipment. The C powders(Op- area of the sample [381 tical pure, Shanghai Carbon Element Factory) were firstly dispersed in deionized water followed by the addition of Sic powders with controlled composition. PVAl788 was 23. Microstructure characterization selected as binder and glycerol as plasticizer. The thickness of C sheets was adjusted to 30 um. Much thinner layer Microstructure characterization was performed by op- were also prepared by the so-called"screen printing"pro- cal microscopy and SEM. Energy dispersive X-ray cess. The surface of each SiC sheets was coated by passing (EDX)spectra were obtained across the interfacial layer the aforementioned C slurries through a 200-mesh screen. to determine the diffusion of elements from adjacent 46-20 um range through the adjustment of solid content of characterize Crack pattern of fractured surface was also The thickness of the interfacial layers was varied in the said slurry. After coating, the sheets were dried and stacked in the repeating sequence of SiC and C-sic layers Subsequently, organic additives were removed by heating to 800C in a flowing argon atmosphere. a slow heating rate was selected to minimize bloating and cracking during py- rolysis, which might result in distortion of the layers. After pyrolysis, the billets were placed in a BN-coated graphite die. Consolidation was performed by hot pressing at 35 MPa under an argon atmosphere at temperature of 1850C for 0.5h 2. 2. Mechanical and microstructure evaluation of Denection Specimens for flexural test were cut and ground into rect- angular bars. A schematic illustration of bending test process for laminated SiC composites is shown in Fig. 1. Three-point bending strength was determined at room temperature on five to six 3 mm x 4 mm x 36 mm bars with a span of 30 mm and a cross head speed of 0.5- min-.Apparent toughness was measured by the single-edge-notched-beam 0.10.2030.40.5 Denection(mm) p→ Fracture toughness 5 三品 s Content of C(wt%)/12 6 20 0.30.4 Content of C in interfacial layers(wt%) Deflection (mm) Fig. 4. Influence of interfacial composition on the mechanical properties Fig. 5. Load-deflection curves of SiC laminates(a)SiC30-C70,(b) of Sic laminates SiC40-C60,(c)SiC50-C50

J.X. Zhang et al. / Ceramics International 30 (2004) 697–703 699 als and Y2O3 (2.85 wt.%) and Al2O3 (2.15%) as sintering additives. Details concerning the aqueous tape casting process could be obtained from previous published papers [36,37]. The thickness of the SiC green tapes was adjusted to ∼150m. To introduce weak interface between SiC layers, thin C–SiC sheets were also prepared by tape casting process using doctor blade equipment. The C powders (Optical pure, Shanghai Carbon Element Factory) were firstly dispersed in deionized water followed by the addition of SiC powders with controlled composition. PVA1788 was selected as binder and glycerol as plasticizer. The thickness of C sheets was adjusted to ∼30m. Much thinner layers were also prepared by the so-called “screen printing” process. The surface of each SiC sheets was coated by passing the aforementioned C slurries through a 200-mesh screen. The thickness of the interfacial layers was varied in the 5–20m range through the adjustment of solid content of the said slurry. After coating, the sheets were dried and stacked in the repeating sequence of SiC and C–SiC layers. Subsequently, organic additives were removed by heating to 800 ◦C in a flowing argon atmosphere. A slow heating rate was selected to minimize bloating and cracking during pyrolysis, which might result in distortion of the layers. After pyrolysis, the billets were placed in a BN-coated graphite die. Consolidation was performed by hot pressing at 35 MPa under an argon atmosphere at temperature of 1850 ◦C for 0.5 h. 2.2. Mechanical and microstructure evaluation of laminated composites Specimens for flexural test were cut and ground into rectangular bars. A schematic illustration of bending test process for laminated SiC composites is shown in Fig. 1. Three-point bending strength was determined at room temperature on five to six 3 mm × 4 mm × 36 mm bars with a span of 30 mm and a cross head speed of 0.5 mm·min−1. Apparent toughness was measured by the single-edge-notched-beam 20 40 60 80 0 250 500 750 1000 20 40 60 0 1500 3000 4500 Work of fracture ( J.m-2) Content of C (wt%) Strength Fracture toughness Content of C in interfacial layers (wt%) Strength (MPa) 6 8 10 12 14 16 18 Fracture toughness (MPa.s-1 ) Fig. 4. Influence of interfacial composition on the mechanical properties of SiC laminates. (SENB) method on test bars of 4 mm high, 3 mm wide and 36 mm long by a three-point bend using a span of 30 mm and a cross head speed of 0.05 mm·min−1. A straight notch with fine diamond saw was introduced with a depth at about 2 mm. Work of fracture was obtained by dividing the area under the load–displacement curve by twice the cross-section area of the sample [38]. 2.3. Microstructure characterization Microstructure characterization was performed by optical microscopy and SEM. Energy dispersive X-ray (EDX) spectra were obtained across the interfacial layer to determine the diffusion of elements from adjacent layers. The crack pattern of fractured surface was also characterized. Fig. 5. Load–deflection curves of SiC laminates (a) SiC30-C70, (b) SiC40-C60, (c) SiC50-C50

J.x. Zhang et al/Ceramics International 30(2004)697-703 3. Results and discussion Table 1 Mechanical properties of interfacial layers 3.1. Interfacial thickness Sample SiC30-C70 SiC50-C50 SiC60-C40 733 1567 Efects of thickness of interfacial layers on the strength, Fracture toughness(MPam/2)0.30 parent toughness and work of fracture of Sic samples are Work of fracture (-) 35.4 shown in Fig. 2 The strength of SiC samples shows an increase trend with the decrease of the thickness of interfacial layers; while the 3.2. Interfacial composition and mechanical properties apparent toughness and work of fracture exhibit a differ- ent character(see Fig. 2). When the interfacial thickness The properties of interfacial layers are adjusted by con- is 3 um, SiC laminates exhibit a catastrophic fracture be- trolling their composition Effects of interfacial composition havior; on the other hand, when the interfacial thickness is on the properties of SiC laminates are shown in Fig 4.The higher than 25 um, graceful failure occurs, the mechanical C-SiC bulk samples with the same composition as interfa- properties of Sic laminates drop altogether. An optimal in- cial layers were also sintered under the same condition for terfacial thickness is shown to be around 10 um(see Fig. 2). comparison. The mechanical properties of these C-SiC bulk The microstructure of fractured surface of SiC samples samples are shown in Table 1 is shown in Fig. 3. The belt between parallel lines is the As shown in Table 1, the addition of SiC powders has very interfacial layer, see Fig. 3(a), the left side(marked as"b) limited effects on the mechanical properties of C-Sic bulk and right side(marked as"")are shown in Fig 3(b)and samples. However, as shown in Fig 4, the mechanical prop- (c), respectively. The SiC layers(left side and right side)are erties of SiC laminates exhibit a considerable dependence well densified. However, it is difficult to detect exactly the on the composition of interfacial layers: the flexural strength layers. This may be due to the diffusion of elements from layers, similar to that of Si3N4 samples [13, 14]. The li,? interface between the interfacial layers and the adjacent decreases constantly with the increase of C in interfac Sic layers, which will be discussed later ture toughness and work of fracture first show an increase 250 (a)SiC40-C60 (b)SiC40-C60 250um 50um (c)SiC50-C50 d) siC60-C40 Fig. 6. Optical micrographs showing the side surface of fexural specimens containing (a)40 vol %,(b)40 vol %,(c)50 vol %, (d)60 vol. SiC in the

700 J.X. Zhang et al. / Ceramics International 30 (2004) 697–703 3. Results and discussion 3.1. Interfacial thickness Effects of thickness of interfacial layers on the strength, apparent toughness and work of fracture of SiC samples are shown in Fig. 2. The strength of SiC samples shows an increase trend with the decrease of the thickness of interfacial layers; while the apparent toughness and work of fracture exhibit a different character (see Fig. 2). When the interfacial thickness is ∼3m, SiC laminates exhibit a catastrophic fracture behavior; on the other hand, when the interfacial thickness is higher than 25 m, graceful failure occurs, the mechanical properties of SiC laminates drop altogether. An optimal interfacial thickness is shown to be around 10 m (see Fig. 2). The microstructure of fractured surface of SiC samples is shown in Fig. 3. The belt between parallel lines is the interfacial layer, see Fig. 3(a), the left side (marked as “b”) and right side (marked as “c”) are shown in Fig. 3(b) and (c), respectively. The SiC layers (left side and right side) are well densified. However, it is difficult to detect exactly the interface between the interfacial layers and the adjacent SiC layers. This may be due to the diffusion of elements from SiC layers, which will be discussed later. Fig. 6. Optical micrographs showing the side surface of flexural specimens containing (a) 40 vol.%, (b) 40 vol.%, (c) 50 vol.%, (d) 60 vol.% SiC in the interfacial layers (after testing). Table 1 Mechanical properties of interfacial layers Sample SiC30-C70 SiC50-C50 SiC60-C40 Strength (MPa) 7.33 15.67 19.33 Fracture toughness (MPa m1/2) 0.30 – 0.34 Work of fracture (J m−2) 10 33.3 35.4 3.2. Interfacial composition and mechanical properties The properties of interfacial layers are adjusted by controlling their composition. Effects of interfacial composition on the properties of SiC laminates are shown in Fig. 4. The C–SiC bulk samples with the same composition as interfacial layers were also sintered under the same condition for comparison. The mechanical properties of these C–SiC bulk samples are shown in Table 1. As shown in Table 1, the addition of SiC powders has very limited effects on the mechanical properties of C–SiC bulk samples. However, as shown in Fig. 4, the mechanical properties of SiC laminates exhibit a considerable dependence on the composition of interfacial layers: the flexural strength decreases constantly with the increase of C in interfacial layers, similar to that of Si3N4 samples [13,14]. The fracture toughness and work of fracture first show an increase

《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_Fracture behavior of laminated SiC composites

《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_Fracture behavior of laminated SiC composites