MATERIALS IENGE& EGEERIG ELSEVIE Materials Science and Engineering A 412(2005)177-181 www.elsevier.com/locate/msea C/C-SiC composites for space applications and advanced friction systems W. Krenkel* Ceramic Materials Engineering, Department of Ceramic Materials, University of Bayreuth, Ludwig-Thoma-Str 36b, D-95440 Bayreuth. Germany Received in revised form 29 July 2005 Ceramic matrix composite materials are being considered the primary materials for hot structures of future launch vehicles. Melt infiltrated based on the liquid silicon infiltration process have proven their suitability under extreme thermo-mechanical environments in different structural parts like nose caps, nozzle jet vanes and engine flaps. Considerable progress has been achieved within the last few years to mature the manufacture technology and to tailor the properties of the materials. Among low densities and high damage tolerance behaviour C/C-SiC composites show superior tribological properties predestining these materials for advanced friction systems O 2005 Elsevier B. v. All rights reserved Keyword: Space applications; Friction systems; Ceramic matrix composites 1. Introduction process was developed which also allows the use of uncoated and non-graphitized fibres [4-71 The liquid silicon infiltration process is based on the impreg- nation of porous carbon/carbon composites by molten silicon 2. C/C-SiC composites for aerospace applications and its reaction to silicon carbide. A fibre preform with an interconnecting network of cracks is infiltrated by liquid sili- 2.1. Process description and microstructure formation con,mostly applying only capillary forces. The application of pressure or the processing in vacuum can improve the infiltra- Generally, carbon fibres show a high amount of active sur- tion process. The temperatures involved are at least beyond the face groups to increase the adhesion with the polymer matrix melting point of silicon(1415C). Typically, the operation tem- Therefore, the use of as-received fibres(without any coatings) perature is in the range of 1600C. The low melt viscosity, the leads to strong fibre/matrix bondings in the carbon fibre rein- high chemical reactivity, the good wetting of the fibre reinforce- forced plastic(CFRP) composite, measured in terms of high ment and the anomaly of silicon during the phase transition interlaminar shear strengths(ILSS). Typical ILSS-values for bi- ( density change of silicon is approximately 8%)are critical pro- directionally reinforced CFRP composites used as preforms for cessing parameters to be considered the LSl-process are in the range of 40-50 MPa irst attempts to infiltrate carbon/carbon composites by liq The CFRP composites are pyrolyzed under inert atmosphere uid silicon have been conducted for more than 20 years[1-3]. (N2) at temperatures between 900 and 1650 C to convert the According to these basic investigations, the surface of the carbon polymer matrix to amorphous carbon. Thermo-optical analy- fibres has to be coated prior to the infiltration of silicon in order sis of the pyrolysis step show that first fibre/matrix debondings to reduce the degree of fibre degradation. Also, highly graphi- in bi-directionally reinforced CFRP composites occur beyond ized carbon fibres are assumed to be mandatory for the fibre 505C [8]. With increasing pyrolysis temperature, the shrink preform because they are more stable in contact with silicon age stresses locally exceed the tensile strength of the matrix, than non-graphitized fibres. Both requirements are contrary to a resulting in a relaxation of the matrix by cracking. In the case of cost-efficient processing of CMCs In the last few years, the LsI- high fibre/matrix bondings(FMB)this procedure repeats several times for each fibre bundle, As a result, a segmentation of the fibre tows occurs and leads to a translaminar microcrack pattern Corresponding author. 49921555501;fax:+49921555502. with dense C/C segments consisting of about 300-500 individ- E-mail address: walter @uni-bayreuth de(w Krenkel) ual fibres. The subsequent infiltration of molten silicon at about 0921-5093/S-see front matter e 2005 Elsevier B V. All rights reserved doi:10.1016 J.msea.200508204
Materials Science and Engineering A 412 (2005) 177–181 C/C–SiC composites for space applications and advanced friction systems W. Krenkel ∗, F. Berndt Ceramic Materials Engineering, Department of Ceramic Materials, University of Bayreuth, Ludwig-Thoma-Str. 36b, D-95440 Bayreuth, Germany Received in revised form 29 July 2005 Abstract Ceramic matrix composite materials are being considered the primary materials for hot structures of future launch vehicles. Melt infiltrated composites based on the liquid silicon infiltration process have proven their suitability under extreme thermo-mechanical environments in different structural parts like nose caps, nozzle jet vanes and engine flaps. Considerable progress has been achieved within the last few years to mature the manufacture technology and to tailor the properties of the materials. Among low densities and high damage tolerance behaviour C/C–SiC composites show superior tribological properties predestining these materials for advanced friction systems. © 2005 Elsevier B.V. All rights reserved. Keyword: Space applications; Friction systems; Ceramic matrix composites 1. Introduction The liquid silicon infiltration process is based on the impregnation of porous carbon/carbon composites by molten silicon and its reaction to silicon carbide. A fibre preform with an interconnecting network of cracks is infiltrated by liquid silicon, mostly applying only capillary forces. The application of pressure or the processing in vacuum can improve the infiltration process. The temperatures involved are at least beyond the melting point of silicon (1415 ◦C). Typically, the operation temperature is in the range of 1600 ◦C. The low melt viscosity, the high chemical reactivity, the good wetting of the fibre reinforcement and the anomaly of silicon during the phase transition (density change of silicon is approximately 8%) are critical processing parameters to be considered. First attempts to infiltrate carbon/carbon composites by liquid silicon have been conducted for more than 20 years [1–3]. According to these basic investigations, the surface of the carbon fibres has to be coated prior to the infiltration of silicon in order to reduce the degree of fibre degradation. Also, highly graphitized carbon fibres are assumed to be mandatory for the fibre preform because they are more stable in contact with silicon than non-graphitized fibres. Both requirements are contrary to a cost-efficient processing of CMCs. In the last few years, the LSI- ∗ Corresponding author. Tel.: +49 921 55 55 01; fax: +49 921 55 55 02. E-mail address: walter.krenkel@uni-bayreuth.de (W. Krenkel). process was developed which also allows the use of uncoated and non-graphitized fibres [4–7]. 2. C/C–SiC composites for aerospace applications 2.1. Process description and microstructure formation Generally, carbon fibres show a high amount of active surface groups to increase the adhesion with the polymer matrix. Therefore, the use of as-received fibres (without any coatings) leads to strong fibre/matrix bondings in the carbon fibre reinforced plastic (CFRP) composite, measured in terms of high interlaminar shear strengths (ILSS). Typical ILSS-values for bidirectionally reinforced CFRP composites used as preforms for the LSI-process are in the range of 40–50 MPa. The CFRP composites are pyrolyzed under inert atmosphere (N2) at temperatures between 900 and 1650 ◦C to convert the polymer matrix to amorphous carbon. Thermo-optical analysis of the pyrolysis step show that first fibre/matrix debondings in bi-directionally reinforced CFRP composites occur beyond 505 ◦C [8]. With increasing pyrolysis temperature, the shrinkage stresses locally exceed the tensile strength of the matrix, resulting in a relaxation of the matrix by cracking. In the case of high fibre/matrix bondings (FMB) this procedure repeats several times for each fibre bundle. As a result, a segmentation of the fibre tows occurs and leads to a translaminar microcrack pattern with dense C/C segments consisting of about 300–500 individual fibres. The subsequent infiltration of molten silicon at about 0921-5093/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2005.08.204
W. KrenkeL, F Berndt Materials Science and Engineering A 412(2005)177-181 1600C rapidly fills the cracks within some minutes. The dense 3. C/C-SiC composites for advanced friction systems carbon matrix inside the fibre bundles shields off the highl reactive silicon. A layer of silicon carbide is formed around the 3. 1. Mechanical and thermo-physical properties segments and only a small amount of lead-bearing carbon fibres are converted and damaged First investigations with respect to brake applications started A thermal treatment of the carbon fibres prior to their imple- in 1994 with C/C-SiC composites using a 2D fibre architec- mentation into the polymer matrix de-activates the fibre surfaces ture with a fibre orientation parallel to the friction surface[12] and reduces the FMB in the polymer stage. Exposing the fibres The disks were tested against pads of the same ceramic mate in inert atmosphere at temperatures beyond 600C removes the rial as no conventionally available pad material sustained the functional surface groups of the fibres to a certain degree, result- high temperatures. This tribological system resulted in surface ing in reduced bonding forces in the fibre-matrix interphase. temperatures of more than 1000C, high coefficients of friction By increasing the pre-treatment temperature beyond 900 C the(CoFand considerably low wear rates. Nevertheless, these first FMB decreases further and the ILSS for the CFRP composite generation C/C-SiC composites were not suitable for an indus- is typically below 20 MPa. During pyrolysis these weak inter- trial use in brake disks and pads, as they were too expensive phases lead to a shrinkage away from the matrix to the fibres, to produce and their Cof was not stable enough. Consequently, resulting in carbon fibre tows without any segmentation. During C/C-SiC composites and adapted processes have to be devel siliconization much more silicon in comparison to composites oped to improve these CMC materials for their applicability in with untreated fibres is absorbed, resulting in higher densities. high-performance brake systems As there is no coating of the fibres used, the liquid silicon ca Different C/C-SiC composites have been developed by react with most of the filaments. This reduces the load-bearing diverse manufacturers, all characterised by low porosities(lower capability of the fibres considerably and the fracture behaviour than 6%), high fibre volume contents(higher than 30%)and of the composite becomes more similar to that of monolithic moderate mechanical properties. Table 1 summarizes the cu ceramics[9,101 rent status of the mechanical and thermo-physical properties of short fibre reinforced C/C-SiC composites, available in the open 2. 2. Aerospace applications literature, in comparison with grey cast iron and carbon/carbon materials [13-20]. Due to the different ceramic and fibre frac The LSI process was established 1990 at the german tions of the composites, the properties vary in a wide range. If Aerospace Center in Stuttgart (DLR)to develop C/C-SiC com- higher mechanical properties are required, e.g. in brake linings posites for space applications. First tests concentrated on the of elevators and cranes, a two-dimensional fibre reinforcement n-fight verification of material samples, which were integrated is preferred. Table 2 gives a complemental overview of the prop- into ablative heat shields. The nose cap of X-38, which was erties of C/C-SiC brake materials with a 2D fibre reinforcement planned to serve as a technology carrier for a new Crew Return As most of this r&d work is conducted under confidentiality. Vehicle of the International Space Station, is regarded as the there is a lack of comparative properties and statistical data. current stage of the materials development for thermal protec- Nevertheless, the variety of published properties demonstrates tion systems(TPS)of spacecraft [11]. It is made of C/C-Sic the high flexibility of the lsi process opposites derived from fabric prepregs using the autoclave technique. The thin-walled shell(wall thickness approximately 3.2. Tribological properties 6 mm)was manufactured in a net-shape technology, realised y the non-destructive evaluation of the microstructure and an The main requirements on new high performance brake mate accurate control of the shrinkage behaviour during all thermal rials are processing steps Much shorter operational times of only some seconds are stable dynamic and static coefficients of friction demanded for jet vanes which are used to divert the direction high wear stability for lifetime brake systems; of thrust in solid fuel rockets of missiles. However, they are low weight to reduce the unsprung mass of the transportation loaded by considerably higher thermo-mechanical stresses than TPS-structures of spacecraft. Advanced jet vanes are made of high degree of freedom in the structural design(e.g for inter- C/C-SiC composites and coated with a ceramic surface pro- nal cooling ducts, attachments) tection(e.g. CVD-SiC) in order to withstand the immense low life cycle costs blast of solid particles (e.g. Al2O3). The tailoring of the microstructure of C/C-Sic composites for jet vanes conse- th transverse heat fluxes from the outer region(friction quently requires a compromise between high fracture toughness surface)to the centre of the composite are necessary to avoid (high carbon fibre contents) and high resistance to abrasion an overheating of the friction surface, i.e. high transverse con- (high SiC contents). Both applications, hot structures for space- ductivities must be adjusted. Standard C/C-SiC composites with craft as well as jet vanes for missiles were designed as lim- bi-directional reinforcements used in hot structures of spacecraft ited life structures, whereas quite longer lifetimes are required have been modified in their composition and microstructure and for terrestrial applications like new brake disks in passenger led to essential improvements. Particularly, by increasing the silicon carbide content of the composite the transverse thermal
178 W. Krenkel, F. Berndt / Materials Science and Engineering A 412 (2005) 177–181 1600 ◦C rapidly fills the cracks within some minutes. The dense carbon matrix inside the fibre bundles shields off the highly reactive silicon. A layer of silicon carbide is formed around the segments and only a small amount of lead-bearing carbon fibres are converted and damaged. A thermal treatment of the carbon fibres prior to their implementation into the polymer matrix de-activates the fibre surfaces and reduces the FMB in the polymer stage. Exposing the fibres in inert atmosphere at temperatures beyond 600 ◦C removes the functional surface groups of the fibres to a certain degree, resulting in reduced bonding forces in the fibre–matrix interphase. By increasing the pre-treatment temperature beyond 900 ◦C the FMB decreases further and the ILSS for the CFRP composite is typically below 20 MPa. During pyrolysis these weak interphases lead to a shrinkage away from the matrix to the fibres, resulting in carbon fibre tows without any segmentation. During siliconization much more silicon in comparison to composites with untreated fibres is absorbed, resulting in higher densities. As there is no coating of the fibres used, the liquid silicon can react with most of the filaments. This reduces the load-bearing capability of the fibres considerably and the fracture behaviour of the composite becomes more similar to that of monolithic ceramics [9,10]. 2.2. Aerospace applications The LSI process was established 1990 at the German Aerospace Center in Stuttgart (DLR) to develop C/C–SiC composites for space applications. First tests concentrated on the in-flight verification of material samples, which were integrated into ablative heat shields. The nose cap of X-38, which was planned to serve as a technology carrier for a new Crew Return Vehicle of the International Space Station, is regarded as the current stage of the material’s development for thermal protection systems (TPS) of spacecraft [11]. It is made of C/C–SiC composites derived from fabric prepregs using the autoclave technique. The thin-walled shell (wall thickness approximately 6 mm) was manufactured in a net-shape technology, realised by the non-destructive evaluation of the microstructure and an accurate control of the shrinkage behaviour during all thermal processing steps. Much shorter operational times of only some seconds are demanded for jet vanes which are used to divert the direction of thrust in solid fuel rockets of missiles. However, they are loaded by considerably higher thermo-mechanical stresses than TPS-structures of spacecraft. Advanced jet vanes are made of C/C–SiC composites and coated with a ceramic surface protection (e.g. CVD–SiC) in order to withstand the immense blast of solid particles (e.g. Al2O3). The tailoring of the microstructure of C/C–SiC composites for jet vanes consequently requires a compromise between high fracture toughness (high carbon fibre contents) and high resistance to abrasion (high SiC contents). Both applications, hot structures for spacecraft as well as jet vanes for missiles were designed as limited life structures, whereas quite longer lifetimes are required for terrestrial applications like new brake disks in passenger cars. 3. C/C–SiC composites for advanced friction systems 3.1. Mechanical and thermo-physical properties First investigations with respect to brake applications started in 1994 with C/C–SiC composites using a 2D fibre architecture with a fibre orientation parallel to the friction surface [12]. The disks were tested against pads of the same ceramic material as no conventionally available pad material sustained the high temperatures. This tribological system resulted in surface temperatures of more than 1000 ◦C, high coefficients of friction (CoF) and considerably low wear rates. Nevertheless, these first generation C/C–SiC composites were not suitable for an industrial use in brake disks and pads, as they were too expensive to produce and their CoF was not stable enough. Consequently, C/C–SiC composites and adapted processes have to be developed to improve these CMC materials for their applicability in high-performance brake systems. Different C/C–SiC composites have been developed by diverse manufacturers, all characterised by low porosities (lower than 6%), high fibre volume contents (higher than 30%) and moderate mechanical properties. Table 1 summarizes the current status of the mechanical and thermo-physical properties of short fibre reinforced C/C–SiC composites, available in the open literature, in comparison with grey cast iron and carbon/carbon materials [13–20]. Due to the different ceramic and fibre fractions of the composites, the properties vary in a wide range. If higher mechanical properties are required, e.g. in brake linings of elevators and cranes, a two-dimensional fibre reinforcement is preferred. Table 2 gives a complemental overview of the properties of C/C–SiC brake materials with a 2D fibre reinforcement. As most of this R&D work is conducted under confidentiality, there is a lack of comparative properties and statistical data. Nevertheless, the variety of published properties demonstrates the high flexibility of the LSI process. 3.2. Tribological properties The main requirements on new high performance brake materials are • stable dynamic and static coefficients of friction; • high wear stability for lifetime brake systems; • low weight to reduce the unsprung mass of the transportation system; • high degree of freedom in the structural design (e.g. for internal cooling ducts, attachments); • low life cycle costs. High transverse heat fluxes from the outer region (friction surface) to the centre of the composite are necessary to avoid an overheating of the friction surface, i.e. high transverse conductivities must be adjusted. Standard C/C–SiC composites with bi-directional reinforcements used in hot structures of spacecraft have been modified in their composition and microstructure and led to essential improvements. Particularly, by increasing the silicon carbide content of the composite the transverse thermal
w. Krenkel, F Berndt/ Materials Science and Engineering A 412(2005)177-181 Table 1 Properties of short fibre reinforced C/C-SiC composites in comparison with grey cast iron and carbon/carbon materials C/C-SiC (short fibre) C/C GJL-250 HITCo/SGL (typica nk SGL carbon DaimlerCh Brembo MS production DLR silca FU2952 sigrasic C-brake 25 2.25 6-1.9 1.71.8 Flexural strength[MPa 320-370 0=140 40-170 Youngs modulus [ gPa 30-35 103-118 Open porosity [ SiC-fraction [ Specific heat [J/kg K] 800-1200 800-1400 Specific heat [J/kg k]at[C] RI1200 RT-1200 1200 CTE⊥[0-6K 10-4.0 1.8-3.0 2.4-2.7 CTEn[10-6K-]at ['C 300 Thermal conductivity 1[W/m 25-30 Thermal conductivity [W/mK] 25 Thermal conductivity n [W/mk] at [C] Process conductivity was doubled in comparison to the original space strate. Depending on this CtE mismatch, a microcracked surface materials [13] occurs as a result of the tensile stresses within the coating during However, high Sic levels and low carbon contents also infu- cooling after processing. The formation of the microcrack pat ence the mechanical properties and decrease the damage tol- tern depends on the fibre architecture of the core material. The erance of the brake disk. As high ceramic contents are mainly most pronounced crack pattern with plenty of randomly orien- necessary in the outer region of the disk, two approaches for a tated cracks can be observed for bi-dimensionally reinforced further material improvement were pursued C/C-SiC composites whose thermal shrinkage during cooling is close to zero in direction of the fibres short fibre reinforce- development of C/C-SiC composites with a gradual increase ments with their higher CTE result in nearly crack-free surfaces of SiC from the centre to the surfaces(functionally graded The width of the microcracks depends on the thickness of the Sic-layer. During braking, when the coating is heated up, the development of homogeneous C/C-Sic composites with cracks get narrower as the outer region expands more than the Si-SiC coatings on the surfaces substrate. All cracks normally run through the total thickness of the layer, but stop in the ductile core region and no breakage of Both approaches successfully fulfil the conflicting require- the fibres occurs ments on high ductility, high hardness and good wear resistance In the last few years, many tribological tests for different The coefficient of thermal expansion(CTE)of the ceramic-rich brake applications have been conducted in order to optimize surface is considerably higher than the CTE of the C/C-SiC sub- C/C-Sic brake disks. In particular for high performance vehi- cles. combinations of C/C-Sic brake disks with organic and intermetallic pads were tested which allow operating times C/C-SiC brake materials with a two-dimensional fibre reinforcement omparable to the lifetime of a car (300,000 km). Most of the test results as well as the material s compositions of the pads are con- C/C-SiC(2D reinforcement) fidential and not published. At least, some values are depicted in Schunk DLR sila DLR silca Figs. 1-2 showing the decisive role of the pad material for high CF226/2 XS and stable CoFs. Small changes in the composition of the pad's material influence the CoF heavily. As a consequence, the tribo- 1.8-1.9 gical behaviour of a new brake system can hardly be predicted Flexural strength[MPa and has to be determined by extensive tests Youngs modulus [GPa] Open porosity [% CTE [10KI 4. Advanced friction systems Thermal conductivity, (W/mK 20 189 Thermal conductivity [W/mk] 30 Due to the high thermal stability and the low specific mass SiC content [ of C/C-SiC composites a great leap in brake technology LSI achievable, combining non-fading characteristics with better 50° C up to 1600°C driving dynamics. Different sports cars from Porsche, Ferrari Si- plus SiC-content and Daimler Chrysler are already equipped with ceramic brakes
W. Krenkel, F. Berndt / Materials Science and Engineering A 412 (2005) 177–181 179 Table 1 Properties of short fibre reinforced C/C–SiC composites in comparison with grey cast iron and carbon/carbon materials C/C–SiC (short fibre) C/C HITCO/SGL GJL-250 (typical) Schunk FU2952 SGL carbon sigrasic DaimlerChrysler C-brake Brembo CCM MS production sicom DLR silca SF Density [g/cm3] 2.0 2.4 2.25 2.25 1.6–1.9 2.0–2.1 1.7–1.8 7.2 Flexural strength [MPa] 65 80 67 – 320–370 90–140 140–170 340 Young’s modulus [GPa] 25 30 30–35 – 75 50–70 50 103–118 Open porosity [%] 160 80 Young’s modulus [GPa] 55 63 41 Open porosity [%] <6 <3 <5 CTE|| [10−6 K−1] – 0.4–2.6a 1.1–2.5a Thermal conductivity⊥ [W/mK] 20 15.3 18.9 Thermal conductivity|| [W/mK] 30 26.3 – SiC content [%] 25 30 50b Process LSI LSI LSI a −50 ◦C up to 1600 ◦C. b Si- plus SiC-content. strate. Depending on this CTE mismatch, a microcracked surface occurs as a result of the tensile stresses within the coating during cooling after processing. The formation of the microcrack pattern depends on the fibre architecture of the core material. The most pronounced crack pattern with plenty of randomly orientated cracks can be observed for bi-dimensionally reinforced C/C–SiC composites whose thermal shrinkage during cooling is close to zero in direction of the fibres. Short fibre reinforcements with their higher CTE result in nearly crack-free surfaces. The width of the microcracks depends on the thickness of the SiC-layer. During braking, when the coating is heated up, the cracks get narrower as the outer region expands more than the substrate. All cracks normally run through the total thickness of the layer, but stop in the ductile core region and no breakage of the fibres occurs. In the last few years, many tribological tests for different brake applications have been conducted in order to optimize C/C–SiC brake disks. In particular for high performance vehicles, combinations of C/C–SiC brake disks with organic and sintermetallic pads were tested which allow operating times comparable to the lifetime of a car (300,000 km). Most of the test results as well as the material’s compositions of the pads are con- fidential and not published. At least, some values are depicted in Figs. 1–2 showing the decisive role of the pad material for high and stable CoFs. Small changes in the composition of the pad’s material influence the CoF heavily. As a consequence, the tribological behaviour of a new brake system can hardly be predicted and has to be determined by extensive tests. 4. Advanced friction systems Due to the high thermal stability and the low specific mass of C/C–SiC composites a great leap in brake technology is achievable, combining non-fading characteristics with better driving dynamics. Different sports cars from Porsche, Ferrari and DaimlerChrysler are already equipped with ceramic brakes
w.Krenkel, F Berndt Materials Science and Engineering A 412(2005)177-181 0.7 D C/C-SiC disk 80 v=23.7ms 言04a=068ms2 03 EE市 iron 0.0 Fig 1. Influence of the pad material on the frictional behaviour of 2D reinforced Fig. 2. Wear rates of C/C-SiC brake disks in combination with commercial C/C-SiC brake disks ining materials(materials composition see Fig. 1). was adapted with six pistons and the brake pads include an insu- and several companies are currently producing C/C-SiC brake lating ceramic back side to prevent the metallic and polymer disks and pads under series conditions brake parts from the high temperature. Additionally, Porsche The Porsche company offers internally ventilated ceramic offers a highly wear resistant dual disk clutch for the Carrera composite brakes(Fig 3)for different car models with a diam- GT model(Fig 3). The clutch plate is made of titanium with eter of 350 mm gaining weight savings of about 50% compared a lining of C/C-SiC, transmitting a maximum torque of more with conventional brake systems. The ceramic brake disk is than 1000 Nm. The small clutch diameter of 169mm leads to ounted on a metallic hub and can resist a maximum applica- a lower gearbox mounting and the reduced mass improves the ion temperature of about 800oC. The aluminium brake calliper motor dynamic Fig. 3. Left: Porsche ceramic composite brake(PCCB); right: Porsche ceramic clutch PCCC (left), in comparison with the conventional clutch 21] Energy per brake of different transportation systems Transportation system Train Aircraft Automotive Elevator(emergency) Crane(emergency) CE I Boeing 777 Porsche GT2 Schindler 700 Mayr roba-stop Max speed (m/s 88.9 Mass[103H Deceleration [m/ Brake energy [M] 1850 1.7 No of brake di Energy per brake disk [M] 5b/ 1.7 a 75% of brake c Emergency
180 W. Krenkel, F. Berndt / Materials Science and Engineering A 412 (2005) 177–181 Fig. 1. Influence of the pad material on the frictional behaviour of 2D reinforced C/C–SiC brake disks. and several companies are currently producing C/C–SiC brake disks and pads under series conditions. The Porsche company offers internally ventilated ceramic composite brakes (Fig. 3) for different car models with a diameter of 350 mm gaining weight savings of about 50% compared with conventional brake systems. The ceramic brake disk is mounted on a metallic hub and can resist a maximum application temperature of about 800 ◦C. The aluminium brake calliper Fig. 2. Wear rates of C/C–SiC brake disks in combination with commercial lining materials (material’s composition see Fig. 1). was adapted with six pistons and the brake pads include an insulating ceramic back side to prevent the metallic and polymer brake parts from the high temperature. Additionally, Porsche offers a highly wear resistant dual disk clutch for the Carrera GT model (Fig. 3). The clutch plate is made of titanium with a lining of C/C–SiC, transmitting a maximum torque of more than 1000 Nm. The small clutch diameter of 169 mm leads to a lower gearbox mounting and the reduced mass improves the motor dynamic. Fig. 3. Left: Porsche ceramic composite brake (PCCB); right: Porsche ceramic clutch PCCC (left), in comparison with the conventional clutch [21]. Table 3 Energy per brake of different transportation systems Transportation system Train Aircraft Automotive Elevator (emergency) Crane (emergency) ICE 1 Boeing 777 Porsche GT2 Schindler 700 Mayr roba-stop Max. speed [m/s] 91.7 72.2 88.9 13.8 30 Mass [103 kg] 440 208 1.7 18 3.1 Deceleration [m/s2] 1.3 2.4 14.5 Brake energy [MJ] 1850 542 6.7 1.7 1.4 No. of brake disks 192 48 4 8 1 Energy per brake disk [MJ] 7.2a 4.5b/20c 1.7 0.21 1.4 a 75% of brake energy. b 40% of brake energy. c Emergency (RTO)
w. Krenkel, F. Berndt /Materials Science and Engineering A 412(2005)177-181 Besides automotive cars, other transportation systems are [4] W. Krenkel, Development of a Cost Efficient Process for the Manu- also under consideration to be equipped with CMC brakes. High facture of CMC Components, Doctoral Thesis, University of Stuttgart, speed trains, aircraft(civil and military)and emergency brakes DLR-Forschungsbericht 2000-2004, 2000. for elevators and cranes are potential candidates. As shown in [ 5] w Krenkel, Proceedings of the Ceramic Engineering and Science,vol 22 Issue 3, American Ceramic Society, 2001, pp. 443-454 Table 3 the requirements differ widely for these braking sys- w. Krenkel, H. Hald, Liquid Infiltrated C/SiC-An Alternative tems, resulting in a wide span ofenergy(between 0. 2 and 20 MJ), for Hot Space Structures in Spacecraft Structures and Mechanical Test- which has to be absorbed in the brake disks. Consequently, there ing, European Space Agency Publications Division, ESASP-289, Paris, are big differences in shape, size and construction of the brake France, 1989, p. 325 disks, comprising solid and thick disks of up to 800 mm in diam- [7R Kochendorfer, w. Krenkel, High-temperature ceramic-matrix com- posites 1: Design durability and performance, in: A.G. Evans, R. Naslain eter(e.g. for trains), internally ventilated disks with ribs and Eds ) Ceramic Transactions, vol. 57, American Ceramic Society, 1995 evolvent-shaped cooling ducts for sports cars and rather thin, p.13-22 fabric-reinforced rotors, stators and linings for emergency brake [8]J. Schulte-Fischedick, M. FrieB, wKrenkel,R. Kochendorfer, M Konig, Proceedings of the 12th International Conference on Composite Mate. rials(ICCM-12), July 5-7, Paris, France, 1999. [9] w. Krenkel, Designing with C/C-SiC composites, in: N.R. Bansal, J. P 5. Summary Singh, W.K.Riven, H. Schneider(Eds ) Advances in Ceramic Matrix Composites IX, vol. 153, Ceramic Transactions, 2003, pp. 103-123 C-fibre reinforced SiC composites( C/C-SiC)can be widely [10]w Krenkel, Ceramic Engineering and Science Proceedings, vol 24, No 4,2003,pp.583-592 tailored in their microstructures and properties. They show supe- [11]H. Hald, H. Weihs, T. Reimer, Proceedings of the 53rd International rior tribological properties in comparison to grey cast iron Astronautical Congress, October 10-19, Houston/Texas, USA, 2002 carbon/carbon. In combination with their low density, high ther-[12]W. Krenkel, Proceedings of the ISATA Conference on Supercars, 31 mal shock resistance and good abrasive resistance, they are October-4 November, Aachen, Germany, 1994 promising candidates for advanced brake and clutch systems. [3]w. Krenkel, B. Heidenreich, R. Renz, Adv. Eng. Mater. 4(7)(2002 High improvements in wear resistance were achieved by func- [14)S. Vaidyaraman, P. Purdy, T. Walker, S. Horst, C/SiC material evaluation Almost wear-free brake disks in combination with acceptable for aircraft brake applications, in: w. Krenkel, R. Naslain, H. Schnei- der(Eds ) High Temperature Ceramic Matrix Composites, Wiley-VCH, low wear rates of the pads show a high potential for lifetime Weinheim, Germany, 2001, Pp. 802-808 brake disks. The future challenges comprise the reduction of the [15]M. Krupka, A Kienzle, Fiber Reinforced Ceramic Composites for Brake material costs and improvements of the quality assurance Discs, SAE Technical Paper Series 2000-01-2761, 2000 [16 R Gadow, M. Speicher, Ceram. Trans. 128(2001)25-41 [17]R Weiss, Carbon fiber reinforced CMCs: manufacture, properties, oxi- dation protection, in: w. Krenkel, R. Naslain, H. Schneider(Eds ) High Temperature Ceramic Matrix Composites, Wiley-VCH, Weinheim Ge [1] C.C. Evans, A.C. Parmee, R.W. Rainbow, Proceedings of Fourth London pp. Conference on Carbon and Graphite, 1974, pp. 231-235 [18 Data sheet from SGL Carbon Group, SIGRASIC 6010 GNJ [2 W B. Hillig, R.L. Mehan, C.R. Morelock, V.l. De Carlo, W. Laskow Faserverstarkte Keramik fur Bremsscheiben, 1998 [3]R. Gadow, Die Silizierung von Kohlenstoff, Doctoral Thesis, University [20] Data sheet from Brembo Brake Systems, 20 brakes.de Ceram.Bul54(12)(1975) [19DatasheetfromSicomGmbh2004,www.sicon of Karlsruhe. 1986 [21] C. Becker, Keramik im Carrera GT, Christophorus 306/Porsche, 2004
W. Krenkel, F. Berndt / Materials Science and Engineering A 412 (2005) 177–181 181 Besides automotive cars, other transportation systems are also under consideration to be equipped with CMC brakes. High speed trains, aircraft (civil and military) and emergency brakes for elevators and cranes are potential candidates. As shown in Table 3 the requirements differ widely for these braking systems, resulting in a wide span of energy (between 0.2 and 20 MJ), which has to be absorbed in the brake disks. Consequently, there are big differences in shape, size and construction of the brake disks, comprising solid and thick disks of up to 800 mm in diameter (e.g. for trains), internally ventilated disks with ribs and evolvent-shaped cooling ducts for sports cars and rather thin, fabric-reinforced rotors, stators and linings for emergency brake systems. 5. Summary C-fibre reinforced SiC composites (C/C–SiC) can be widely tailored in their microstructures and properties. They show superior tribological properties in comparison to grey cast iron or carbon/carbon. In combination with their low density, high thermal shock resistance and good abrasive resistance, they are promising candidates for advanced brake and clutch systems. High improvements in wear resistance were achieved by functionally graded C/C–SiC composites or by ceramic coatings. Almost wear-free brake disks in combination with acceptable low wear rates of the pads show a high potential for lifetime brake disks. The future challenges comprise the reduction of the material costs and improvements of the quality assurance. References [1] C.C. Evans, A.C. Parmee, R.W. Rainbow, Proceedings of Fourth London Conference on Carbon and Graphite, 1974, pp. 231–235. [2] W.B. Hillig, R.L. Mehan, C.R. Morelock, V.I. DeCarlo, W. Laskow, Ceram. Bull. 54 (12) (1975). [3] R. Gadow, Die Silizierung von Kohlenstoff, Doctoral Thesis, University of Karlsruhe, 1986. [4] W. Krenkel, Development of a Cost Efficient Process for the Manufacture of CMC Components, Doctoral Thesis, University of Stuttgart, DLR-Forschungsbericht 2000–2004, 2000. [5] W. Krenkel, Proceedings of the Ceramic Engineering and Science, vol. 22 Issue 3, American Ceramic Society, 2001, pp. 443–454. [6] W. Krenkel, H. Hald, Liquid Infiltrated C/SiC—An Alternative Material for Hot Space Structures in Spacecraft Structures and Mechanical Testing, European Space Agency Publications Division, ESASP-289, Paris, France, 1989, p. 325. [7] R. Kochendorfer, W. Krenkel, High-temperature ceramic–matrix com- ¨ posites I: Design durability and performance, in: A.G. Evans, R. Naslain (Eds.), Ceramic Transactions, vol. 57, American Ceramic Society, 1995, pp. 13–22. [8] J. Schulte-Fischedick, M. Frieß, W. Krenkel, R. Kochendorfer, M. K ¨ onig, ¨ Proceedings of the 12th International Conference on Composite Materials (ICCM-12), July 5–7, Paris, France, 1999. [9] W. Krenkel, Designing with C/C–SiC composites, in: N.R. Bansal, J.P. Singh, W.K. Kriven, H. Schneider (Eds.), Advances in Ceramic Matrix Composites IX, vol. 153, Ceramic Transactions, 2003, pp. 103–123. [10] W. Krenkel, Ceramic Engineering and Science Proceedings, vol. 24, No. 4, 2003, pp. 583–592. [11] H. Hald, H. Weihs, T. Reimer, Proceedings of the 53rd International Astronautical Congress, October 10–19, Houston/Texas, USA, 2002. [12] W. Krenkel, Proceedings of the ISATA Conference on Supercars, 31 October–4 November, Aachen, Germany, 1994. [13] W. Krenkel, B. Heidenreich, R. Renz, Adv. Eng. Mater. 4 (7) (2002) 427–436. [14] S. Vaidyaraman, P. Purdy, T. Walker, S. Horst, C/SiC material evaluation for aircraft brake applications, in: W. Krenkel, R. Naslain, H. Schneider (Eds.), High Temperature Ceramic Matrix Composites, Wiley-VCH, Weinheim, Germany, 2001, pp. 802–808. [15] M. Krupka, A. Kienzle, Fiber Reinforced Ceramic Composites for Brake Discs, SAE Technical Paper Series 2000-01-2761, 2000. [16] R. Gadow, M. Speicher, Ceram. Trans. 128 (2001) 25–41. [17] R. Weiss, Carbon fiber reinforced CMCs: manufacture, properties, oxidation protection, in: W. Krenkel, R. Naslain, H. Schneider (Eds.), High Temperature Ceramic Matrix Composites, Wiley-VCH, Weinheim Germany, 2001, pp. 440–456. [18] Data sheet from SGL Carbon Group, SIGRASIC 6010 GNJ, Faserverstarkte Keramik f ¨ ur Bremsscheiben, 1998. ¨ [19] Data sheet from Sicom GmbH, 2004, www.sicon-brakes.de. [20] Data sheet from Brembo Brake Systems, 2002, www.brembo.com. [21] C. Becker, Keramik im Carrera GT, Christophorus 306/Porsche, 2004
