《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_slurry infiltration and hot pressing.pdf_大学文库

c00.52es and manufacturing ELSEVIER opposites: Part A 32(2001)1021-1029 Fabrication of fiber-reinforced celsian matrix composites N.P. Bansal,".J.A. Setlock National Aeronautics and Space Administration, John H. Glenn Research Center, Cleveland, OH 44135-3191, USA Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, USA Abstract A method has been developed for the fabrication of small diameter, multifilament tow, fiber-reinforced ceramic matrix composites. Its application has been successfully demonstrated for the Hi-Nicalon/celsian system. Strong and tough celsian matrix composites, reinforced with BN/SiC-coated Hi-Nicalon fibers, have been fabricated by infiltrating the fiber tows with the matrix slurry, winding the tows on a drum, utting and stacking of the prepreg tapes in the desired orientation, and hot pressing. The monoclinic celsian phase in the matrix was produced in situ, during hot pressing, from the 0.75Bao-025SrO-Al2O3-2SiO2 mixed precursor synthesized by solid state reaction from metal oxides. Hot pressing resulted in almost fully dense fiber-reinforced composites. The unidirectional composites having 42 vol % o of fibers exhibited graceful failure with extensive fiber pullout in three-point bend tests at room temperature. values of yield stress and strain were 435 35 MPa and 0.27 + 0.01%, respectively, and ultimate strengths of 900 t 60 MPa were observed. Youngs modulus of the omposites was measured to be 165 +5 GPa. C 2001 Elsevier Science Ltd. All rights reserved Keywords: A Ceramic-matrix composites(CMCs): Celsian: B Mechanical properties 1. Introduction sian, and the orthorhombic phase are found only in synthetic products. The hexacelsian phase is thermodynamically Monoclinic celsian BaAl2Si2O8(BAS)and SrAlSi2O stable at temperatures between 1590C and the melting (SAS)are refractory materials having melting points higher point whereas the celsian phase is stable at temperatures than 1700.C. These materials are resistant to oxidation and below 1590C. however. hexacelsian can exist as a meta reduction and also show reasonably good resistance to alkali stable phase at all temperatures from 1590C to room ttack. These materials are phase stable up to.C and ture. At -300C. hexacelsian chemically compatible with alumina, mullite and silicon reversible structural transformation [7] into the orthorhor nitride (in inert or nitrogen atmospheres) at elevated bic form, accompanied by a large volume change of -3%0 temperatures. They show low values of dielectric constant Thus, hexacelsian is an undesirable phase and loss tangent which make them promising materials for In both the BAs and SAs systems, hexacelsian is always electromagnetic windows or radome applications [1] at high the first phase to form. However, on heat treatment at temperatures, packaging for microelectronics, high voltage -1200C or higher temperatures, its transformation into condensers and other electric insulating products. Celsian is the monoclinic phase is very sluggish in BAS [8] and very lso useful as an environmental barrier coating for SiC!Sic rapid in SAs [9]. It is known that doping of BAs with SAs composites and protects against the loss of silica as volatile accelerates the hexacelsian to monoclinic celsian transfor- silicon hydroxide species in the combustion products in mation [10]. Fortunately, BAS and SAs form solid solutions turbine engines at elevated temperatures [2]. Celsian is in the entire composition range [1, 10]. The starting compo- also being investigated as a matrix material for fiber-rein- sition of 0.75Bao-025SrO-Al2O3-2SiO,(BSAS)was forced composites [3-6] for high temperature structural used for the synthesis of monoclinic celsian in the present applications in hot sections of turbine engines study BAS exists in three different polymorphs, the monoclinic, Processing and properties of celsian glass-ceramic hexagonal, and orthorhombic phases. The monocline matrix composites reinforced with large diameter CVD phase, commonly known as celsian, is the naturally occur- SiC SCS-6 monofilaments [3-6] and the multifilament ring phase. The hexagonal phase, also known as hexacel- small diameter Nicalon [11] and HPZ [12] fibers have been described earlier. The objective of this study was to Corresponding author. Tel. +1-216-433-3855; fax: +1-216-433-5544 develop the fabrication of small diameter, multifilament tow E-mail address: narottamp bansal@lerc. nasa. gov(N P. Bansal) fiber-reinforced celsian matrix composites. Microstructures 9-835X/01/S- see front matter 2001 Elsevier Science Ltd. All rights reserved. S1359-835X(00)00169-X

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P. Bansal, J.A. Setlock/Composites: Part A 32(2001)1021-1029 A- BaAl2O4 2500 B-Ba2SiO4 C-Ba Sr2 A207 500 B BAcA 20, deg Fig 3. Powder XRD pattern of the mixed 0.75BaCO3-0 25SrCO3 -Al2O3-2Sio powder calcined at 915'C for 20 h in air. grinding. A small part of the calcined powder was loaded dual surface layer of BN overcoated with Sic were used in into a graphite die and hot pressed at 1300C for 2-3 h the present study. The fiber coatings were applied by a under 27. 5 MPa (4 ksi) pressure. commercial vendor using a continuous chemical vapor Polymer derived Hi-Nicalon fiber tows(1800 denier, 500 deposition(CVD)reactor. The Bn coating was deposited filaments/tow) with low oxygen content produced by at -1000C utilizing a proprietary precursor and was amor- Nippon Carbon Co were used as the reinforcement. These phous to partly turbostratic in nature. A thin overcoating of fibers have an average diameter of -14 um; a report Sic was also deposited by CVD onto the BN-coated fibers 14, 15] chemical composition(wt %)of 62.4% Si, 37 The SiC layer was crystalline. The nominal coating thick- C, and 0.5%O; and C/Si atomic ratio of -1.39. The Hi- nesses were 0. 4 um for BN and 0.3 um for SiC. The BN Nicalon fibers mainly consist of Sic microcrystals with an interfacial layer acts as a weak, crack-deflecting phase average grain size of 4 nm and amorphous carbon. These while the Sic overcoat acts as a barrier to diffusion of fibers have a density of 2.7 g/cm, room temperature tensile boron from bn into the oxide matrix and also prevents strength of -2.8 GPa, elastic modulus of 270 GPa, and an diffusion of matrix elements into the fiber. average coefficient of thermal expansion of 3.5 x 10 /C A sketch of the set-up used for infiltration of the matrix from room temperature to 500"C. Hi-Nicalon fibers having a slurry into the fiber tows is shown in Fig. 1. This is similar to 1000 25 eg Fig. 4. XRD spectra from the surface of a hot pressed plate of Bao.7sSro25Al2Si2Os. All the diffraction peaks match with the monoclinic celsian phase

N P. Bansal, J.A. Setlock /Composites: Part A 32(2001)1021-1029 99818Fn 888225KV Fig. 7. SEM micrographs showing polished cross-section of a unidirectional Hi-Nicalon/BN/SIC/BSAS cor followed by hot pressing under vacuum in a graphite die. curves recorded in three-point flexure using an Instron The hot pressed fiber-reinforced composite panel was 4505 universal testing instrument at a crosshead speed of surface polished and sliced into test bars(50.4 mm 1. 27 mm/min (0.05 in /min) and support span (L)of x6.4 mm x1.9 mm) for mechanical testing. 40 mm. Strain gauges were glued to the tensile surfaces TGA of the calcination process was carried out at a of the flexure test bars. Stress was calculated using beam heating rate of 5C/min under flowing air(60 ml/min) theory. The yield stress was calculated from the stress from room temperature to 1500C using a Perkin-Elmer strain curves from the point where the curve deviates TGA-7 system which was interfaced with a computerized from linearity Elastic modulus of the composite was deter data acquisition and analysis system. X-ray diffraction mined from the linear portion of the stress-strain curve (XRD) patterns were recorded at room temperature using to the yield point using linear interpolation a step scan procedure (0.02/26 step, time per step 0.5 or I s)on a Philips ADP-3600 automated diffractometer equipped with a crystal monochromator employing CuK a 3 Results and discussion adiation. density was measured from dimensions and mass as well as by the archimedes method. Microstruc The TGA curve of the mixed BSAS powder consisting of tures of the polished cross-sections and fracture surfaces metal carbonates and oxides is shown in Fig. 2. Minor were observed in an optical microscope as well as in a weight loss near room temperature is due to evaporation JEOL JSM-840A scanning electron microscope (SEM). of the residual moisture and acetone. A major event showing For transmission electron microscopy (TEM), thin foils a large weight loss, due to the decomposition of barium and of the composite samples were prepared by slicing, polish- strontium carbonates into oxides, is observed between -750 ing, dimple grinding, and argon ion beam milling. A thin and 1000.C. A calcination temperature of 900-920C was carbon coating was evaporated onto the TEM thin foils and chosen for decomposition of the carbonates. The mixed the SEM specimens for electrical conductivity prior to powder was calcined at this temperature for 20-24 h analysis. The thin foils were examined in a Philips air TGA analysis of this calcined powder showed no further EM400T operating at 120 keV. X-ray elemental analyses weight loss indicating complete decomposition of the metal on the tEM were acquired using a Kevex thin window carbonates during the calcination step. energy dispersive spectrometer(EDS) and analyzer. The XRD pattern of the mixed powder, calcined at Mechanical properties were determined from stress-strain -915C for 20 h in air, is presented in Fig. 3. SiO2

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P. Bansal, J.A. Setlock/Composites: Part A 32(2001)1021-1029 in Table 1. The fiber volume fraction in the composites was calculated to be -42%. From their densities, the composites ppear to be almost fully dense. The XRD pattern taken from the polished surface of the hot pressed composite was similar to that shown in Fig. 3. Monoclinic celsian was the only crystalline phase present and the undesired hexacelsian phase was not detected from XRD. This implies that the desired, thermodynamically stable, monoclinic celsian phase is formed in situ, from the mixed oxides recursor, during hot pressing of the composite. Doping with Sro facilitates 9, 10 the formation of monoclinic celsian in the matrix. In a recent study [17], a minor amount Fig 9. EDS spectra from(a)the coarsened BN region and(b) the corre of hexacelsian phase has been detected in the matrix using ponding microdiffraction pattern Raman micro-spectroscopy SEM micrographs taken from the polished cross-section (a-quartz) and BaAlO were the major phases preser of the unidirectional hot pressed composite are shown Small amounts of Ba2SiO4, a-Al2O3, and Ba2Sr2Al2O, Fig. 7. Uniform fiber distribution and good matrix infiltra- were also identified. Fig 4 shows the XRD pattern taken tion within the fiber tows is evident. Some of the filaments from the surface of a monolithic sample made by hot press- are of irregular shape rather than having circular cross- ing the precalcined powder at 1300.C for 2 h under section. The manufacturer reports an average fiber diameter 27.5 MPa(4 ksi). All the XRD peaks correspond to the of -14 um, but a large variation in the diameter of the monoclinic celsia filaments within a fiber tow can be seen. The BN/SiC undesirable hexacelsian phase. surface coating has been detached from some of the fibers SEM micrographs showing the surface and the cross- during metallography or composite processing Debonding tions of the BN/SiC coated Hi-Nicalon fibers are given or loss of the fiber coating may lead to adverse reactions in Fig. 5. The coatings on some of the fibers appear to be between the fibers and the oxide matrix at high temperature smooth and of uniform thickness whereas on other fibers the resulting in strong fiber -matrix bonding coating is very thick and granular. SEM micrographs taken TEM micrographs showing the fiber/matrix interface from the polished cross-sections of the fibers are shown in region of the Hi-Nicalon/BN/SIC/BSAS composite ig. 6. The double coating on the fiber surface is clearly presented in Fig 8. The BN visible. The dark layer is BN and the bright layer is Sic. layers as seen in Fig. 8(a). From EDS analysis, the fiber/BN Some of the composite physical characteristics are given interface was found to be rich in C along with the presence 800 08 10 Fig. 10. Stress-strain curves recorded in three-point flexure for unidirectional Hi-Nicalon/BN/SiC/BSAS composites hot pressed under(a) less and(b)more aggressive conditions

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1028 N P Bansal, J.A. Setlock/Composites: Part A 32(2001)1021-1029 Table 2 Room temperature mechanical properties of Hi-Nicalon fiber-reinforced Baa7sSro2s Al Si2Os celsian composites(Unidirectional; 12 Plies)(Measured in three- point flexure Yield Ultimate Ultimate content. modulus E(GPa) (MPa) (MPa) HI-NIC-BSAS-1-29. 9 BN/SiC 0.283 0.258 HI-NIC-BSAS-1-31-96 BN/SiC 0.42 0.283 0.771 Fig. 11. SEM micrographs from the fracture surfaces of unidirectional Nicalon/BNSIC/BSAS composites showing extensive fiber pullout; composites hot pressed under(a) less and(b)more aggressive condit of Si and O. The Sic overcoating was often found to be and elastic modulus of 160-170 GPa were observed. The missing from the BN/matrix interface, but was intact in this measured elastic modulus is in good agreement with a particular case. A crack running along the fiber/BN interface value of 169 GPa, calculated from the rule-of-mixtures may also be seen. The bn coating, when viewed via the (Ec= VmEm V Er where V is the volume fraction and TEM, did reveal an internal reaction. Some areas show no the subscripts c, m, and f refer to the composite, matrix, evidence of coarsening(Fig. &a) while others show varying and fiber, respectively) using Em=96 GPa[13]and Er amounts of reaction. Fig 8(b)shows coarsening of three Bn 270 GPa[14, 15]. Values of yield strain and the ultimate layers, from outside in towards the fiber, during hot pressing strain are -0.26-0.28% and -0.6-0.8%, respectively of the composite. However, the fiber/BN interface and the SEM micrographs of fracture surfaces of the two inner BN layer remain unchanged. EDS spectra obtained composites, after the three-point flexure tests, are shown from the coarsened region(Fig. 9a) show no obvious in Fig. 11. Extensive long lengths of fiber pullout are chemical changes in the various BN layers. Corresponding microdiffraction patterns(Fig. 9b) show coarsening to the point where individual diffraction spots are seen. It may be pointed out that reaction through all four BN layers or visi- ble degradation of the fiber was never observed. The sic layer remains apparently unaffected. Typical stress-strain curves recorded in three-point flex ure for the unidirectional BSAS matrix composites rein- forced with BN/SiC-coated Hi-Nicalon fibers hot pressed at two different temperatures are shown in Fig. 10. The fiber volume in the composites was%. Both the compo- sites show graceful failure. The values of yield stress, oy, yield strain, Ey, elastic modulus, E, ultimate strength, ou, and ultimate strain, Eu, of the composites hot pressed at two ifferent temperatures are given in Table 2. Values of yield Fig. 12. SEM micrograph from the polished cross-section of a unidirec- stress of 400-470 MPa, ultimate strength of 850-960 MPa tional Hi-Nicalon/BN/SiC/BSAS composite after the flexure test

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N.P. Bansal, J.A. Setlock/Composites: Part A 32(2001)1021-1029 1029 observed indicating toughening behavior. An sem micro- References graph of the polished cross-section of a Hi-Nicalon/BN/ BSAS composite, formed under more aggressive processing [1] Talmy IG. Haught DA. Ceramics in the system BaO-AlO3'2SiO2- conditions and flexure tested at room temperature under SrOAlOr 2SiO2 for advanced radome application. Naval Surface ambient conditions, is presented in Fig. 12. Debonding at the Warfare Center Technical Report. NSWC TR 89-162, September, fiber-matrix interface and crack deflection around the rein- [2] Lee KN. Current status of environmental barrier coatings for Si-based forcing fibers is observed, indicating a tough composite. The ceramics. Presented at The Intemational Conference on Metallic results of this study clearly indicate that reinforcement of Coatings and Thin Films(ICMCTF), San Diego, CA, April 10-14, BSAS matrix with Hi-Nicalon fibers having a duplex BN/ SiC coating results in a strong and tough composite at room [3] Bansal NP. Ceramic fiber reinforced glass-ceramic matrix compo- temperature. site. US Patent 5, 214, 004, May 25, 1993. [4] Bansal NP. Method of producing a silicon carbide fiber reinforced strontium aluminosilicate glass-ceramic matrix composite. US Patent 4. Summary 5,389,321, February14.1995 [5 Bansal NP. CVD SiC fiber-reinforced barium aluminosilicate ass-ceramic matrix composites. Mater Sci Engng. A Hot pressing of a mixed powder of BSAs composition 1996:220(1-2):129-39 obtained from calcination of metal carbonates and oxides 6 Bansal NP. Formation of monoclinic celsian in silicon results in monoclinic celsian with complete absence of the fiber-reinforced barium aluminosilicate undesirable hexacelsian phase. A method has been developed composites. NASA Technical Memorandum 10699 for the fabrication of small diameter multifilament tow fiber- reinforced ceramic matrix composites. BN/SiC-coated Hi- [7] Takeuchi Y. A detailed investigation of the structure of hexagonal BaAl2Si2Os with reference to its a-B inversion. Miner J Jp Nicalon fiber-reinforced monoclinic celsian composites have been produced by impregnation of the matrix slurry into the [8] Bahat D. Kinetic study on the hexacelsian-celsian phase transforma- ber tows, winding the tows on a drum cutting and stacking of tion. J Mater Sci 1970: 5: 805-10 the prepreg tapes, and hot pressing. Strong, tough, and almost transformation in SrAlSiyOs J Am Ceram Soc 1993: 76(5): 1321-4 fully dense unidirectional composites having -42 vol of [10] Bansal NP, Hyatt MJ, Drummond CH Crystallization and properties fibers were obtained. These composites exhibited graceful of Sr-Ba aluminosilicate glass-ceramic matrices. Ceram Engng sci failure with extensive fiber pull out in a three-point flexure Proc1991;12(7-8):122-34 test. The yield stress of -400-470 MPa and ultimate strength [11] Bansal NP, McCluskey P, Linsey G, Murphy D, Levan G Nicalon high as 960 MPa have been observed. The yield strain was fiber-reinforced celsian glass-ceramic matrix composites. Proceed- -0. 26-0.28%. The Youngs modulus of the composite was ings of Annual HITEMP Review, Cleveland, OH. October 23-25 measured to be -165 GPa 1995. NASA Conference Proceedings 10178, vol 3, 1995.p41-1- 41-14 [12] Bansal NP Processing and properties of HPz fiber-reinforced celsian 5 Conclusions c matrix composites, In preparation. [13] Bansal NP. Solid state synthesis and properties of monoclinic celsian. J Mater Sci1998:33(19):4711-5 It may be concluded that reinforcement of the monoclinic [14] Takeda M, Sakamoto J, Imai Y, Ichikawa H, Ishikawa T Properties of celsian with BN/SiC-coated Hi-Nicalon fiber results in stoichiometric silicon carbide fiber derived from polycarbosilane almost fully dense composites which are strong and tough Ceram Engng Sci Proc 1994: 15(4): 133-41 at room temperature [15] Takeda M, Sakamoto J, Saeki S, Imai Y, Ichikawa H. High silicon carbide fiber Hi-Nicalon for ceramic matrix sites. Ceram Engng Sci Proc 1995: 16(4): 37-44. Acknowledgements [16] Prewo KM. Fiber-reinforced glasses and glass-ceramics. In: Lewis MH, editor. Glasses and Glass-Ceramics. New York: Chapman Thanks are due to Rob Dickerson, Terry Kacik, Ron Hall1989.p.336-68. [17] Gouadec G, Colomban P, Bansal NP. Raman study of Hi-Nicalon Phillips and Ralph Garlick for technical assistance during fiber reinforced celsian matrix composites. Part 1: distribution and this research nanostructure of different phases. J Am Ceram Soc, in press

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《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_slurry infiltration and hot pressing

《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_slurry infiltration and hot pressing