《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_fiber100.pdf_大学文库

Energy Conters. Mgmr Vol 38. No, 10-13, pp. 1035-1 Pergamon All rights reserved. Printed in Great PI:S01%689049)001331 0196-8904/9751700+0.00 ADVANCED MATERIALS AND COATINGS FOR ENERGY CONVERSION SYSTEMS GEORGE R ST PIERRE Department of Materials Science and Engineering. The Ohio State University, 2041 N. College Road Columbus, OH 43210-1178, U.S.A Abstract--Following an historical review of the development of high-temperature alloys for energy advances In single intermetallics, metal-matrix composites, and ceramic-matrix composites are discussed. Particular attention is directed at creep phenomena, fatigue properties, and oxidation resistance. Included within the discussions is the current status of carbon/carbon co aposites as potential high-temperature engineering materials and the development of coating systems for thermal barrier and oxidation protection. The of combustion gas compositions, i.e., oxidation potential, sulfur, halides, etc. are nt list of eligible advanced materials and coatings systems is presented and assessed failure mechanism and life-prediction parameters for some of the new classes of terials are elaborated with the view to achieving affordability and extended life with a high degree of reliability. Examples are drawn from a variety of energy conversion systems. c 997 Elsevier Science Ltd High temperature materials Oxidation Superalloys Carbon/carbon composites INTRODUCTION From the development of thermodynamic principles, it became clear that engine efficiency improves with increased operating temperature and lowered heat rejection temperature. In application rotating engines, this was referred to as the Brayton concept [1]. Gas turbines were used for electric power generation by 1904. The early twentieth century also saw the development of austenitic stainless steels and the 80/20", nickel-chromium alloy. Hence, engine performance improved with the development of high-temperature alloys. Around 1930, the coherent precipitation-strengthened gamma prime"alloys were discovered and calledsuperalloys".In the ensuing years gradual improvements in high-temperature alloys were achieved as illustrated in Fig. 1 from Ohnabe et al [2]. These gains in performance of high-temperature alloys resulted from: improved understanding of microstructure/property relationships; improved control of composition and microstructure during processing; and development of advanced methods for oxidation resistance and creep strength. Table 1 from Kim [3], illustrates the current status of superalloys and some titanium aluminide candidate materials. The creep properties of selected alloys are illustrated in Fig. 2 from In addition, recent attention has been focused on ceramic materials and carbon/carbon composites for high-temperature structural applications as illustrated in Fig. 3 where specific strength is shown as a function of temperature [2]. In still more advanced material developments, multilayered materials, ceramic fiber composites and nanostrured materials are under investigation. Although many critical properties must be carefully evaluated and controlled for all materials insure reliable performance, we may focus our attention on creep strength and oxidation resistance The densities and service temperature range for some selected materials is shown in Fig 4 from Dimiduk ef al. [4]. Included in Fig. 4 are some of the experimental niobium-based intermetallics with projected higher operating temperatures. again, it must be remembered that these materials have not been qualified through processing and performance tests. Sims [1] has related very

Pergamon Energy Convers. Mgmt Vol. 38, No. 10-13, pp. 1035-1041, 1997 © 1997 Elsevier Science Ltd All rights reserved. Printed in Great Britain Pll: S0196-8904(96)00133-1 0196-8904/97 $17.00 + 0.00 ADVANCED MATERIALS AND COATINGS FOR ENERGY CONVERSION SYSTEMS GEORGE R. ST. PIERRE Department of Materials Science and Engineering, The Ohio State University, 2041 N. College Road, Columbus, OH 43210-1178, U.S.A. Abstract--Following an historical review of the development of high-temperature alloys for energy conversion systems including turbine engines, some of the current advances in single crystal materials. intermetallies, metal-matrix composites, and ceramic-matrix composites are discussed. Particular attention is directed at creep phenomena, fatigue properties, and oxidation resistance. Included within the discussions is the current status of carbon/carbon co" Lposites as potential high-temperature engineering materials and the development of coating systems for thermal barrier and oxidation protection. The specific influences of combustion gas compositions, i.e., oxidation potential, sulfur, halides, etc. are discussed. A current list of eligible advanced materials and coatings systems is presented and assessed. Finally, the critical failure mechanism and life-prediction parameters for some of the new classes of advanced structural materials are elaborated with the view to achieving affordability and extended life with a high degree of reliability. Examples are drawn from a variety of energy conversion systems. © 1997 Elsevier Science Ltd. High temperature materials Oxidation Superalloys Carbon/carbon composites INTRODUCTION From the development of thermodynamic principles, it became clear that engine efficiency improves with increased operating temperature and lowered heat rejection temperature. In application to rotating engines, this was referred to as the Brayton concept [1]. Gas turbines were used for electric power generation by 1904. The early twentieth century also saw the development of austenitic stainless steels and the "80/20", nickel--chromium alloy. Hence, engine performance improved with the development of high-temperature alloys. Around 1930, the coherent precipitation-strengthened "gamma prime" alloys were discovered and called "superalloys". In the ensuing years gradual improvements in high-temperature alloys were achieved as illustrated in Fig. 1 from Ohnabe et al. [2]. These gains in performance of high-temperature alloys resulted from: improved understanding of microstructure/property relationships; improved control of composition and microstructure during processing; and development of advanced methods for oxidation resistance and creep strength. Table 1 from Kim [3], illustrates the current status of superalloys and some titanium aluminide candidate materials. The creep properties of selected alloys are illustrated in Fig. 2 from Dimiduk et al., [4]. In addition, recent attention has been focused on ceramic materials and carbon/carbon composites for high-temperature structural applications as illustrated in Fig. 3 where specific strength is shown as a function of temperature [2]. In still more advanced material developments, multilayered materials, ceramic fiber composites and nanostrured materials are under investigation. Although many critical properties must be carefully evaluated and controlled for all materials to insure reliable performance, we may focus our attention on creep strength and oxidation resistance as two principal criteria. CURRENT STATUS The densities and service temperature range for some selected materials is shown in Fig. 4 from Dimiduk et al. [4]. Included in Fig. 4 are some of the experimental niobium-based intermetaUics with projected higher operating temperatures. Again, it must be remembered that these materials have not been qualified through processing and performance tests. Sims [1] has related very 1035

ST PIERRE: ENERGY CONVERSION SYSTEMS Recession rate Fractional xposed are 0016002000240028003200 Fig. 9. Schematic illustration of critical temperature regime and eed for sealant that for SiC in the in-plane direction. with complex three-dimensional weaving in the preparation of C/C composites it might be possible to reduce these differences. However, in a structural component there would always be some regions in which the Si3N4 or SiC coating(conversion plus deposition) is developed on the in-plane direction of the C/C. The protective coatings are developed at high temperature, Fig. 7. H ence, upon cooling, the coating is put in tension and a pattern of cracks develops. If the crack pattern is tight and regular and the coating is not too thick, the coating may be stable against spalling. In such cases, the cracks may reversibly close upon reheating and reopen again upon cooling. At high temperature, the coating is protective; however, in the intermediate temperature region it is susceptible to localized oxidative attack as illustrated in Fig. 8. Analysis of this phenomenon [6] yields oxidation rate curves represented in Fig 9. Clearly, active inhibitors and sealants are necessary to protect C/C composites during heating and cooling through these temperature regimes. Otherwise severe burn out occurs at the base of the crack. Appropriate sealants that operate repeatedly and consistently in this manner have not been proven. However, it has been demonstrated that SiC or Si3, coated C/C composites have excellent oxidation resistance when held near 1600.C for extended time Functionally graded coatings hold some promise for protection of alloys; however, it is difficul to apply this concept to C/C composites Ceramic fiber materials are fascinating to consider particularly as we learn more about the nature of the fiber-matrix interface and"pull-out"phenomena. Present ceramic materials are still limited by the inherent strength creep properties illustrated in Fig. 3. Also, some of the most promising fibers are highly susceptible to oxidation Some interesting and difficult materials protection problems arise where exposure to halogens nd sulfur occurs, e.g. hot corrosion. Some of the newer coated systems show promise in this regard CONCLUDING COMMENTS Remarkable advances have been made in developing alloys, intermetallics and ceramic fiber materials during the twentieth century. Much lowered creep and oxidation rates are now achievable. These materials have enabled marked improvement in the efficiency and performance of turbines, jet engines and other energy conversion systems. Advances during the next decade will depend upon our ability to improve the microstructure and composition of our candidate systems and to achieve fuller understanding of the microstructure/property relationships. It will be necessary to demonstrate that our advanced material systems can exhibit fully reliable performance under the broad spectrum of conditions arising in energy conversion syste

1040 ST. PIERRE: ENERGY CONVERSION SYSTEMS • 0.010 ~R 0.008 o.oo6 ecession Rate 0 " ! Temperature (F) Fig. 9. Schematic illustration of critical temperature regime and the need for sealants. that for SiC in the in-plane direction. With complex three-dimensional weaving in the preparation of C/C composites it might be possible to reduce these differences. However, in a structural component there would always be some regions in which the Si3N4 or SiC coating (conversion plus deposition) is developed on the in-plane direction of the C/C. The protective coatings are developed at high temperature, Fig. 7. Hence, upon cooling, the coating is put in tension and a pattern of cracks develops. If the crack pattern is tight and regular and the coating is not too thick, the coating may be stable against spalling. In such cases, the cracks may reversibly close upon reheating and reopen again upon cooling. At high temperature, the coating is protective; however, in the intermediate temperature region it is susceptible to localized oxidative attack as illustrated in Fig. 8. Analysis of this phenomenon [6] yields oxidation rate curves represented in Fig. 9. Clearly, active inhibitors and sealants are necessary to protect C/C composites during heating and cooling through these temperature regimes. Otherwise severe burn out occurs at the base of the crack. Appropriate sealants that operate repeatedly and consistently in this manner have not been proven. However, it has been demonstrated that SiC or Si3N4 coated C/C composites have excellent oxidation resistance when held near 1600°C for extended time. Functionally graded coatings hold some promise for protection of alloys; however, it is difficult to apply this concept to C/C composites. Ceramic fiber materials are fascinating to consider particularly as we learn more about the nature of the fiber-matrix interface and "pull-out" phenomena. Present ceramic materials are still limited by the inherent strength/creep properties illustrated in Fig. 3. Also, some of the most promising fibers are highly susceptible to oxidation. Some interesting and difficult materials protection problems arise where exposure to halogens and sulfur occurs, e.g. hot corrosion. Some of the newer coated systems show promise in this regard. CONCLUDING COMMENTS Remarkable advances have been made in developing alloys, intermetallics and ceramic fiber materials during the twentieth century. Much lowered creep and oxidation rates are now achievable. These materials have enabled marked improvement in the efficiency and performance of turbines, jet engines and other energy conversion systems. Advances during the next decade will depend upon our ability to improve the microstructure and composition of our candidate systems and to achieve fuller understanding of the microstructure/property relationships. It will be necessary to demonstrate that our advanced material systems can exhibit fully reliable performance under the broad spectrum of conditions arising in energy conversion systems

《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_fiber100

《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_fiber100