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Stressed oxidation behaviors of SiC matrix composites in combustion environments
Materials Letters 61 (2007) 4114 – 4116 www.elsevier.com/locate/matlet
Stressed oxidation behaviors of SiC matrix composites in combustion environments Xin'gang Luan ⁎, Laifei Cheng, Yongdong Xu, Litong Zhang National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, P.R. China Received 29 August 2006; accepted 11 January 2007 Available online 23 January 2007
Abstract Performance of three kinds of continuous fiber reinforced SiC matrix composites prepared by chemical vapor infiltration (CVI) method, i.e. 2D C/SiC, 3D C/SiC and 3D SiC/SiC composites, have been investigated in the high temperature combustion environment gas with various creep stresses. The relationship between the life time of composite and the normalized peak strength, defined by the ratio of the test stress to the material strength, was studied. The life time of composites decreased with increasing the normalized peak strength following an exponential relationship. The oxidation resistance of the SiC/SiC composite was the best and that of the 2D C/SiC composite was the worst in the high temperature combustion environment with an applied stress. The experimental results suggested that there was a critical normalized peak strength which controls the oxidation mechanism of C/SiC. Below the critical normalized peak strength, the degradation of C/SiC in the combustion environment was controlled by the diffusion of oxygen and water vapor through the cracks in the composite. Above the critical normalized peak strength, the degradation was controlled by the oxidation of C fibers. © 2007 Elsevier B.V. All rights reserved. Keywords: Composites; Stress oxidation; Combustion environment; Creep
1. Introduction Ceramic matrix composite (CMC) materials will be one of the major contributions towards meeting the future propulsion needs by providing a significant potential improvement on fuel consumption and thrust-to-weight ratio compared with metallic materials. The low specific weight and high specific strength over a large temperature range compared to current nickel base superalloys, and their great damage tolerance compared to monolithic ceramics make this material extremely interesting as structural materials. The introduction of CMC materials into future combustor liners and turbine airfoil components will provide a major step towards realizing reduced component weights and cooling flow requirements [1,2]. Tests of C/SiC and SiC/SiC composites have been carried out in combustion atmospheres followed by analysis and
⁎ Corresponding author. Tel.: +86 029 8849 4622; fax: +86 029 8849 4620. E-mail address: [email protected] (X. Luan). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.01.038
comparison of the oxidation behaviors [3–10]. The oxidation resistance of the SiC/SiC composites was better than that of the C/SiC composites. The degradation mechanism has been determined from measurements of the residual strength of the sample and micrographs of the fracture face after the test. It was suggested that the oxidation of the interlayer and the fibers was responsible for the degradation of the composites. The degradation of the static components (i.e., combustor linears) has been assessed by the above-mentioned work; however, less information about the degradation of the dynamic components (i.e., turbine airfoil) is known. The purpose of this work is to evaluate the stressed oxidation of C/SiC and SiC/SiC composites in combustion environments to determine the degradation mechanism from microscopy and strain curves. 2. Experimental Carbon fiber (T-300, Japan Toray) and Silicon carbide fiber (Nicalon™ Japan ) were used. The 3D fiber preform was braided by a two-step method. The 2D fiber perform was prepared by the
X. Luan et al. / Materials Letters 61 (2007) 4114–4116
4115
Fig. 1. Length change of the 3D C/SiC composite in the combustion environment with stress during the testing.
layup of fabrics. The volume fraction of fiber was controlled in the range of 40–45%. The composites were prepared by a lowpressure chemical vapor infiltration (LPCVI) process. The preform was deposited with pyrolytic carbon (PyC) as an interlayer and densified with SiC as a matrix using butane and methyltrichlorosilane (MTS), respectively. The dog bone shaped specimens with dimensions of approximately 185 mm long, 3 mm thick and 3 mm wide in the gage section, were machined from the received composite. Finally, the two-layer SiC coatings with each layer of about 20 μm thickness were prepared by chemical vapor deposition (CVD) from MTS/H2. The specimens were tested in a high temperature combustion environment coupled with a creep stress until fracture. The test environment was obtained from the combustion of aircraft fuel in air. The fuel to oxidant ratio was 0.036, the total pressure was 1 atm and the gas velocity was 240 m/s. The temperature of the combustion gases were 1300 °C detected by a platinum– rhodium thermocouple during testing. The stresses, which are applied by hydraulic servo frame (INSRTON 8872), were 40, 60, 80 and 100 MPa, respectively. The strain curves were
Fig. 2. Length change of the 3D SiC/SiC composite in the combustion environment with stress during the testing.
Fig. 3. Microscopy of fracture section of 3D C/SiC exposed in 1300 °C combustion environment with normalized peak strength of (a) 0.24 and (b) 0.47.
recorded during the test. The fracture faces were observed by SEM. 3. Results and discussion The length changes of the 3D C/SiC composite and the 3D SiC/SiC composite in the 1300 °C combustion environment with the various normalized peak strengths during the testing were shown in Figs. 1 and 2, respectively. The critical normalized peak strength which controls the oxidation mechanism was between 0.35–0.47 for the 3D C/SiC composite
Fig. 4. Life time of composites in 1300 °C combustion environment with different normalized peak strengths.
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X. Luan et al. / Materials Letters 61 (2007) 4114–4116
Table 1 Fabricated tensile strength of composites Material
2D C/SiC
3D C/SiC
3D SiC/SiC
Strength ⁎ (MPa) Standard deviation
272 9.4
170 11.3
456 25.5
⁎ Average value of three results.
suggested by the curves shown in Fig. 1. Below the critical normalized peak strength, a stepwise increase of the sample length was found before the sample break which resulted from the intermittent fiber pullout and fibers fracture. This was attributed to the non-uniform oxidation of the pull-out fibers which was controlled by gas diffusion, as shown in Fig. 3(a). Above the critical normalized peak strength, the continuous fiber fracture resulted in a quasi-linear increase of the sample length. This was due to the uniform oxidation of pull-out fibers which was controlled by the reaction of the carbon fiber with oxygen and water vapor, as shown in Fig. 3(b). The stepwise increase of the sample length shown in Fig. 2 showed that the critical normalized peak strength for the 3D SiC/SiC composite was more than 0.22. Below the critical percentage, the degradation of the 3D SiC/Si C composite was controlled by gas diffusion. The lifetimes of the three kinds of composites exposed in the 1300 °C combustion environment with various normalized peak strengths are shown in Fig. 4. An exponential relationship was followed by the life time of the 2D C/SiC composite. The same relationship will also be followed by the 3D C/SiC composite because of the similar oxidation mechanism. It was found that the life time of 3D SiC/SiC composite was longest and that of the 2D C/SiC composite was shortest under the same normalized peak strength. According to the strength of the three kinds of composites listed in Table 1, it was concluded that there was another factor to affect the life time of the C/SiC composites besides fabricated strength; otherwise the life time of the 2D C/SiC should be longer than that of the 3D C/SiC because of the higher fabricated strength. The structure of the fiber preform was the other factor that affected the life time of C/SiC because this was the only difference between the 2D and the 3D C/SiC composite that we studied. The 3D C/SiC composite has the better oxidation resistance than the 2D composite because it has a more complex structure to slow down the gas diffusion and more fibers to carry the stress in the stress direction. The oxidation resistance of fibers also affected the life time of the composite as seen by comparing the life time of the 3D SiC/SiC with that of the 3D C/SiC.
4. Conclusions In the high temperature combustion environment with the stress, the oxidation resistance of the 3D SiC/SiC composite was best and that of the 2D C/SiC composite was worst.
The oxidation mechanism of composites was controlled by the critical normalized peak strength. Below the critical normalized peak strength, the oxidation was controlled by gas diffusion. Above the critical normalized peak strength, the oxidation was controlled by the reaction of fiber with oxygen and water vapor. In the same atmospheres, the fabricated composite strength, the fiber preform structure and the fiber oxidation resistance were the factors which impacted the life time of the composites. Acknowledgements The authors acknowledge the financial support of the Natural Science Foundation of China (Contract No.90405015), National young Elitists Foundation (Contract No. 50425208) and program for Changjiang Scholars and Innovative Research Team in University. References [1] D.G. LaChapelle, M.E. Noe, W.G. Edmondson, H.J. Stegemiller, J.D. Steibel, D.R. Chang. AIAA 98–3266. [2] S. Beyer, S. Schmidt, G. Cahuzac, R. Meistring, M. Bouchez. AIAA 2004–4019. [3] Cheng Laifei, Xu Yongdong, Zhang Litong, Yin Xiaowei, Carbon 38 (15) (2000) 2103–2108. [4] X. Yin, L. Cheng, L. Zhang, Y. Xu, J. Li, Composites Science and Technology 61 (7) (2001) 977–980. [5] Cheng Laifei, Xu Yongdong, Zhang Litong, Yin Xiaowei, Composites. Part A, Applied Science and Manufacturing 31 (9) (2000) 1015–1020. [6] D. Filsinger, S. Munz, A. Schulz, S. Wittig, G. Anrees, Journal of Engineering for Gas Turbines and Power 123 (2) (2001) 271–276. [7] N. Okabe, I. Murakami, H. Hirata, Y. Yoshioka, H. Ichikawa, Ceramic Engineering and Science Proceedings 16 (5) (1995) 885–892. [8] Sanokawa Yutaka, Ido Yasuji, Sohda Yoshio, Nakazawa Norio, Kaya Hiroshi, Ceramic Engineering and Science Proceedings 18 (4) (1997) 221–228. [9] P. Lipetzky, W.B. Hillig, Proceedings of the Engineering Foundation Conference, 1997, Sponsored by: TMS Minerals, Metals and Materials Soc (TMS), 1997, pp. 359–367. [10] Michael J. Verrilli, Greg Ojard, Terry R. Barnett, Jiangang Sun, George Baaklini, Ceramic Engineering and Science Proceedings 23 (3) (2002) 551–562.
Stressed oxidation behaviors of SiC matrix composites in combustion environments Xin'gang Luan ⁎, Laifei Cheng, Yongdong Xu, Litong Zhang National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, P.R. China Received 29 August 2006; accepted 11 January 2007 Available online 23 January 2007
Abstract Performance of three kinds of continuous fiber reinforced SiC matrix composites prepared by chemical vapor infiltration (CVI) method, i.e. 2D C/SiC, 3D C/SiC and 3D SiC/SiC composites, have been investigated in the high temperature combustion environment gas with various creep stresses. The relationship between the life time of composite and the normalized peak strength, defined by the ratio of the test stress to the material strength, was studied. The life time of composites decreased with increasing the normalized peak strength following an exponential relationship. The oxidation resistance of the SiC/SiC composite was the best and that of the 2D C/SiC composite was the worst in the high temperature combustion environment with an applied stress. The experimental results suggested that there was a critical normalized peak strength which controls the oxidation mechanism of C/SiC. Below the critical normalized peak strength, the degradation of C/SiC in the combustion environment was controlled by the diffusion of oxygen and water vapor through the cracks in the composite. Above the critical normalized peak strength, the degradation was controlled by the oxidation of C fibers. © 2007 Elsevier B.V. All rights reserved. Keywords: Composites; Stress oxidation; Combustion environment; Creep
1. Introduction Ceramic matrix composite (CMC) materials will be one of the major contributions towards meeting the future propulsion needs by providing a significant potential improvement on fuel consumption and thrust-to-weight ratio compared with metallic materials. The low specific weight and high specific strength over a large temperature range compared to current nickel base superalloys, and their great damage tolerance compared to monolithic ceramics make this material extremely interesting as structural materials. The introduction of CMC materials into future combustor liners and turbine airfoil components will provide a major step towards realizing reduced component weights and cooling flow requirements [1,2]. Tests of C/SiC and SiC/SiC composites have been carried out in combustion atmospheres followed by analysis and
⁎ Corresponding author. Tel.: +86 029 8849 4622; fax: +86 029 8849 4620. E-mail address: [email protected] (X. Luan). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.01.038
comparison of the oxidation behaviors [3–10]. The oxidation resistance of the SiC/SiC composites was better than that of the C/SiC composites. The degradation mechanism has been determined from measurements of the residual strength of the sample and micrographs of the fracture face after the test. It was suggested that the oxidation of the interlayer and the fibers was responsible for the degradation of the composites. The degradation of the static components (i.e., combustor linears) has been assessed by the above-mentioned work; however, less information about the degradation of the dynamic components (i.e., turbine airfoil) is known. The purpose of this work is to evaluate the stressed oxidation of C/SiC and SiC/SiC composites in combustion environments to determine the degradation mechanism from microscopy and strain curves. 2. Experimental Carbon fiber (T-300, Japan Toray) and Silicon carbide fiber (Nicalon™ Japan ) were used. The 3D fiber preform was braided by a two-step method. The 2D fiber perform was prepared by the
X. Luan et al. / Materials Letters 61 (2007) 4114–4116
4115
Fig. 1. Length change of the 3D C/SiC composite in the combustion environment with stress during the testing.
layup of fabrics. The volume fraction of fiber was controlled in the range of 40–45%. The composites were prepared by a lowpressure chemical vapor infiltration (LPCVI) process. The preform was deposited with pyrolytic carbon (PyC) as an interlayer and densified with SiC as a matrix using butane and methyltrichlorosilane (MTS), respectively. The dog bone shaped specimens with dimensions of approximately 185 mm long, 3 mm thick and 3 mm wide in the gage section, were machined from the received composite. Finally, the two-layer SiC coatings with each layer of about 20 μm thickness were prepared by chemical vapor deposition (CVD) from MTS/H2. The specimens were tested in a high temperature combustion environment coupled with a creep stress until fracture. The test environment was obtained from the combustion of aircraft fuel in air. The fuel to oxidant ratio was 0.036, the total pressure was 1 atm and the gas velocity was 240 m/s. The temperature of the combustion gases were 1300 °C detected by a platinum– rhodium thermocouple during testing. The stresses, which are applied by hydraulic servo frame (INSRTON 8872), were 40, 60, 80 and 100 MPa, respectively. The strain curves were
Fig. 2. Length change of the 3D SiC/SiC composite in the combustion environment with stress during the testing.
Fig. 3. Microscopy of fracture section of 3D C/SiC exposed in 1300 °C combustion environment with normalized peak strength of (a) 0.24 and (b) 0.47.
recorded during the test. The fracture faces were observed by SEM. 3. Results and discussion The length changes of the 3D C/SiC composite and the 3D SiC/SiC composite in the 1300 °C combustion environment with the various normalized peak strengths during the testing were shown in Figs. 1 and 2, respectively. The critical normalized peak strength which controls the oxidation mechanism was between 0.35–0.47 for the 3D C/SiC composite
Fig. 4. Life time of composites in 1300 °C combustion environment with different normalized peak strengths.
4116
X. Luan et al. / Materials Letters 61 (2007) 4114–4116
Table 1 Fabricated tensile strength of composites Material
2D C/SiC
3D C/SiC
3D SiC/SiC
Strength ⁎ (MPa) Standard deviation
272 9.4
170 11.3
456 25.5
⁎ Average value of three results.
suggested by the curves shown in Fig. 1. Below the critical normalized peak strength, a stepwise increase of the sample length was found before the sample break which resulted from the intermittent fiber pullout and fibers fracture. This was attributed to the non-uniform oxidation of the pull-out fibers which was controlled by gas diffusion, as shown in Fig. 3(a). Above the critical normalized peak strength, the continuous fiber fracture resulted in a quasi-linear increase of the sample length. This was due to the uniform oxidation of pull-out fibers which was controlled by the reaction of the carbon fiber with oxygen and water vapor, as shown in Fig. 3(b). The stepwise increase of the sample length shown in Fig. 2 showed that the critical normalized peak strength for the 3D SiC/SiC composite was more than 0.22. Below the critical percentage, the degradation of the 3D SiC/Si C composite was controlled by gas diffusion. The lifetimes of the three kinds of composites exposed in the 1300 °C combustion environment with various normalized peak strengths are shown in Fig. 4. An exponential relationship was followed by the life time of the 2D C/SiC composite. The same relationship will also be followed by the 3D C/SiC composite because of the similar oxidation mechanism. It was found that the life time of 3D SiC/SiC composite was longest and that of the 2D C/SiC composite was shortest under the same normalized peak strength. According to the strength of the three kinds of composites listed in Table 1, it was concluded that there was another factor to affect the life time of the C/SiC composites besides fabricated strength; otherwise the life time of the 2D C/SiC should be longer than that of the 3D C/SiC because of the higher fabricated strength. The structure of the fiber preform was the other factor that affected the life time of C/SiC because this was the only difference between the 2D and the 3D C/SiC composite that we studied. The 3D C/SiC composite has the better oxidation resistance than the 2D composite because it has a more complex structure to slow down the gas diffusion and more fibers to carry the stress in the stress direction. The oxidation resistance of fibers also affected the life time of the composite as seen by comparing the life time of the 3D SiC/SiC with that of the 3D C/SiC.
4. Conclusions In the high temperature combustion environment with the stress, the oxidation resistance of the 3D SiC/SiC composite was best and that of the 2D C/SiC composite was worst.
The oxidation mechanism of composites was controlled by the critical normalized peak strength. Below the critical normalized peak strength, the oxidation was controlled by gas diffusion. Above the critical normalized peak strength, the oxidation was controlled by the reaction of fiber with oxygen and water vapor. In the same atmospheres, the fabricated composite strength, the fiber preform structure and the fiber oxidation resistance were the factors which impacted the life time of the composites. Acknowledgements The authors acknowledge the financial support of the Natural Science Foundation of China (Contract No.90405015), National young Elitists Foundation (Contract No. 50425208) and program for Changjiang Scholars and Innovative Research Team in University. References [1] D.G. LaChapelle, M.E. Noe, W.G. Edmondson, H.J. Stegemiller, J.D. Steibel, D.R. Chang. AIAA 98–3266. [2] S. Beyer, S. Schmidt, G. Cahuzac, R. Meistring, M. Bouchez. AIAA 2004–4019. [3] Cheng Laifei, Xu Yongdong, Zhang Litong, Yin Xiaowei, Carbon 38 (15) (2000) 2103–2108. [4] X. Yin, L. Cheng, L. Zhang, Y. Xu, J. Li, Composites Science and Technology 61 (7) (2001) 977–980. [5] Cheng Laifei, Xu Yongdong, Zhang Litong, Yin Xiaowei, Composites. Part A, Applied Science and Manufacturing 31 (9) (2000) 1015–1020. [6] D. Filsinger, S. Munz, A. Schulz, S. Wittig, G. Anrees, Journal of Engineering for Gas Turbines and Power 123 (2) (2001) 271–276. [7] N. Okabe, I. Murakami, H. Hirata, Y. Yoshioka, H. Ichikawa, Ceramic Engineering and Science Proceedings 16 (5) (1995) 885–892. [8] Sanokawa Yutaka, Ido Yasuji, Sohda Yoshio, Nakazawa Norio, Kaya Hiroshi, Ceramic Engineering and Science Proceedings 18 (4) (1997) 221–228. [9] P. Lipetzky, W.B. Hillig, Proceedings of the Engineering Foundation Conference, 1997, Sponsored by: TMS Minerals, Metals and Materials Soc (TMS), 1997, pp. 359–367. [10] Michael J. Verrilli, Greg Ojard, Terry R. Barnett, Jiangang Sun, George Baaklini, Ceramic Engineering and Science Proceedings 23 (3) (2002) 551–562.