Current Opinion in Materials science PERGAMON Current Opinion in Solid State and Materials Science 5(2001)283-289 Ceramics for future power generation technology: fiber reinforced oxide composites DB all*.JB. Day Rockwell Science Center. 1049 Camino Dos Rios. Thousand Oaks. CA 91360. USA Major advances have been made during the past 2 years in the development of fiber-reinforced oxide composites for long-life combustion components. These include demonstration of long-term stability of mullite-based porous-matrix composites at 1200C, development of fiber coating and slurry infiltration methods to produce composites with weakly bonded La-monazite interphases, and development of new alumina-based fibers. o 2001 Elsevier Science Ltd. All rights reserved eywords: Ceramics, Power generation technology, Fiber-reinforced oxide composites; Long-life combustion components; Alumina-based fibers, Porus matrix: Weak interface: La-monazite 1. Introduction temperatures, processing r infiltration of the matrix into fiber preforms been developed to the The need for high temperature ceramic composites for degree of sophistication for chemical vapor he power generation industry(both land-based and trans- infiltration, melt infiltration and polymer precursor infiltra- portation) to achieve significant gains in efficiency and tion of SiC; and until recently, weakly bonded interphases, reductions in NO, emissions is well established. Typical a key ingredient needed for damage tolerance(cf. carbon components include combustors, exhaust components, high or BN in SiC-based composites) were not available or even temperature ducts, thermal insulation, heat exchangers and identified. During the period covered by this review, 1999 hot gas filters. Engine and burner rig testing during the past and 2000, key advances have been made towards overcom- few years have demonstrated encouraging progress, the ing each of these limitations. See Refs. 3, 4,59] for reviews result of 20 years of world-wide research. However, the of testing has also shown that the long-term survival of Three approaches have been taken to design micro- Sic-containing composites, the materials which have re- structures of oxide composites that are damage tolerant ceived the vast majority of attention to date, can be limited All aim to prevent damage(cracking) in the matrix from by recession of the matrix by volatility of Sio, scale in crossing to the fibers, thereby allowing the dissipation of combustion environments containing water vapor [1, 21, stress concentrations while retaining the high strengths of contrary to previous expectations that oxidation embrittle- the fibers. Two of these are analogous to the conventional ment would be life-limiting. The undesirable need for approach taken with SiC-based composites, based on fiber environmental barrier coatings to protect these composites coatings that bond weakly, if at all, to the surface of the adds motivation to develop oxide composite systems that fibers, or coatings that are inherently weak(e.g, layered or are inherently stable in oxidizing environments porous). The third relies on the weakness and low stiffness However, oxide composites introduce a new set of of a porous matrix itself to prevent damage from extending imitations:their development is relatively immature, into the fibers, even though the interface between the fibers having received widespread attention only during the past and matrix might be strongly bonded. Tough composites years,the available fibers are not as microstructurally that show wood-like fracture have now been demonstrated able or creep resistant as non-oxide fibers at high using all three approaches. The key remaining challenges are to optimize high temperature properties, demonstrate long-term stability in high-temperature combustion en ding author. Tel. +1-805-373-4170. vironments, and develop robust economical manufacturing ress:dbmarsha@rsc.rockwell.com(.B.Marshall) methods 1359-0286/01/S- see front matter 2001 Elsevier Science Ltd. All rights reserved PII:S1359-0286(01)00017-1
Current Opinion in Solid State and Materials Science 5 (2001) 283–289 Ceramics for future power generation technology: fiber reinforced oxide composites D.B. Marshall , J.B. Davis * Rockwell Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91360, USA Abstract Major advances have been made during the past 2 years in the development of fiber-reinforced oxide composites for long-life combustion components. These include demonstration of long-term stability of mullite-based porous-matrix composites at 12008C, development of fiber coating and slurry infiltration methods to produce composites with weakly bonded La-monazite interphases, and development of new alumina-based fibers. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Ceramics; Power generation technology; Fiber-reinforced oxide composites; Long-life combustion components; Alumina-based fibers; Porus matrix; Weak interface; La-monazite 1. Introduction temperatures; processing methods for infiltration of the matrix into fiber preforms have not been developed to the The need for high temperature ceramic composites for degree of sophistication available for chemical vapor the power generation industry (both land-based and trans- infiltration, melt infiltration and polymer precursor infiltraportation) to achieve significant gains in efficiency and tion of SiC; and until recently, weakly bonded interphases, reductions in NO emissions is well established. Typical a key ingredient needed for damage tolerance (cf. carbon x components include combustors, exhaust components, high or BN in SiC-based composites) were not available or even temperature ducts, thermal insulation, heat exchangers and identified. During the period covered by this review, 1999 hot gas filters. Engine and burner rig testing during the past and 2000, key advances have been made towards overcomfew years have demonstrated encouraging progress, the ing each of these limitations. See Refs. [3,4,59] for reviews result of 20 years of world-wide research. However, the of developments before 1999. testing has also shown that the long-term survival of Three approaches have been taken to design microSiC-containing composites, the materials which have re- structures of oxide composites that are damage tolerant. ceived the vast majority of attention to date, can be limited All aim to prevent damage (cracking) in the matrix from by recession of the matrix by volatility of SiO scale in crossing to the fibers, thereby allowing the dissipation of 2 combustion environments containing water vapor [1,2], stress concentrations while retaining the high strengths of contrary to previous expectations that oxidation embrittle- the fibers. Two of these are analogous to the conventional ment would be life-limiting. The undesirable need for approach taken with SiC-based composites, based on fiber environmental barrier coatings to protect these composites coatings that bond weakly, if at all, to the surface of the adds motivation to develop oxide composite systems that fibers, or coatings that are inherently weak (e.g., layered or are inherently stable in oxidizing environments. porous). The third relies on the weakness and low stiffness However, oxide composites introduce a new set of of a porous matrix itself to prevent damage from extending limitations: their development is relatively immature, into the fibers, even though the interface between the fibers having received widespread attention only during the past and matrix might be strongly bonded. Tough composites 5 years; the available fibers are not as microstructurally that show wood-like fracture have now been demonstrated stable or creep resistant as non-oxide fibers at high using all three approaches. The key remaining challenges are to optimize high temperature properties, demonstrate long-term stability in high-temperature combustion en- *Corresponding author. Tel.: 11-805-373-4170. vironments, and develop robust economical manufacturing E-mail address: dbmarsha@rsc.rockwell.com (D.B. Marshall). methods. 1359-0286/01/$ – see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S1359-0286(01)00017-1
D B. Marshall, J.B. Davis Current Opinion in Solid State and Materials Science 5(2001)283-20 2. Fiber developments erties of such composites see Refs. [*16, 17]. The optimum strength for the matrix in such composites The major constraint on further development of oxide involves a trade-off of properties: the matrix strength must during processing of the matrix and during use. The between a broken fiber and its neighbors, whereas a low highest performance fibers that are now available in matrix strength leads to poor off-axis properties, compres- adequate quantities and at reasonable cost are fine-grained sive strength, and erosion/abrasion resistance. The major high-purity alumina(Nextel 610) and alumina/mullite challenge is to ensure the high temperature stability of the (Nextel 720")fibers produced by the 3M company. The optimum microstructure creep, grain growth and strength characteristics of these The earliest work on porous matrix composites used fibers are now well documented [*5, 6]. The Nextel 610 silica-based matrices [18], which place a restrictive limit fibers have the higher strengths(3.3 GPa, cf. 2. 1 GPa) on high temperature stability. Recent measurements from a and are expected to be more corrosion resistant in certain composite produced by geae (Gen IV ), consisting of environments, whereas the Nextel 720 fibers are more stacked layers of woven alumina fibers(Nextel 610)in an creep resistant and stable to higher temperatures. Based on alumino-silicate matrix, indicate a significant loss in data presently available, the anticipated maximum tem- properties and embrittlement at 950C [19]. The high peratures for extended use are about 1 100C for the Nextel temperature tensile strengths were reduced compared with 610 and 1200 C for the Nextel 720(but dependent on room temperature values by 15 and 50% for unnotched and tress levels and lifetimes) notched test specimens, while observations of fracture a promising approach for improving the creep resist- morphologies indicated a large reduction in the degree of Ice of the alumina fibers has been exploited in a new uncorrelated fiber fracture and pullout. Significant notch fiber (Nextel 650")from 3M[+7. These fibers contain sensitivity was observed even at room temperature(30% 1%Y2O3 as well as -10% ZrO2, based on studies reduction in net-section strength). Large improvements showing that doping of grain boundaries in bulk poly- were seen in another alumino-silicate matrix composite crystalline alumina with Y or La leads to large reductions with more stable mullite fibers(Nextel 720), with no effect in creep and grain growth [8]. Improvements were of notches on net section strength at temperatures up to achieved in the creep resistance compared with Nextel 1100.C, and small effect at 1200.C(20% reduction)[20 610, although the creep rates remain higher than those of However, under creep conditions the effect of notches was the mullite-containing Nextel 720 fibers. Most of the stronger (-40% reduction in net section strength at properties of the new fibers fall between those of Nextel 1100.C)[21], while long-term aging at temperatures of 1 100C and above caused significant reductions in ro main on the role of the ZrO, in changing the properties temperature strengths(60% reduction at 1200C)/222om 610 and Nextel 720. Some interesting questions re and in the relative amounts of Y,O3 in the grain A major advance for porous matrix composites came boundaries and in solid solution in the zro with the development of a mullite-based matrix consisting Further increases in temperature capabilities of poly- of relatively large(l um)mullite powder particles, which crystalline oxide fibers are possible with multi-phase are resistant to sintering, forming a continuous network microstructures designed to resist creep and grain growth bonded together with smaller alumina particles (-0.2 um) or with other systems such as YAG. However, large which sinter more readily [14, 15]. Zirconia has also beer increases will be difficult, for the fine grain sizes required used as the more readily sintered phase [23]. With a to achieve high strengths lead to relatively rapid creep and processing temperature(1200C) close to the limit of the grain growth. Laboratory-scale fabrication of polycrystal- most refractory oxide fibers presently available(Nextel line mullite fibers with promising, but very preliminary 720), these or related matrix compositions appear to offer property data have been reported [9]. Several groups are the most promising prospects for long-term stability developing directionally solidified alumina/YAG eutectic Recent high temperature aging experiments with a 2-D fibers, which if they could be produced in small sizes and woven mullite-alumina composite(formed from multiple large quantities would provide very large increases in layers of fabric)[24] have demonstrated that room-tem- temperature capabilities and expand the options for matrix perature tensile properties were not degraded after aging for 1000 h at temperatures up to 1200C in air, as shown in Fig. 1. The 0/90 strengths and failure strains were unchanged(Fig. 1), while the +45 strength, Youngs 3. Weak(porous)matrix composites modulus, and matrix hardness all increased after aging at the highest temperature. The increases indicate that the effectiveness of the porous matrix concept in mullite/alumina matrix underwent some degree of sinter- allowing damage-tolerant composites without the presence ing during the aging period. Under the same conditions, of fiber coatings was previously demonstrated [14, 15]. Fo the previously mentioned alumino-silicate composites suf- up-to-date accounts of the design and mechanical prop- fered strength loss of more than 60%
284 D.B. Marshall, J.B. Davis / Current Opinion in Solid State and Materials Science 5 (2001) 283–289 2. Fiber developments erties of such composites see Refs. [**16,*17]. The optimum strength for the matrix in such composites The major constraint on further development of oxide involves a trade-off of properties: the matrix strength must composites in the near future will be the temperature limit be low enough to prevent damage in the matrix from imposed by the microstructural stability of the fibers, both extending into the fibers and to prevent transfer of stress during processing of the matrix and during use. The between a broken fiber and its neighbors, whereas a low highest performance fibers that are now available in matrix strength leads to poor off-axis properties, compresadequate quantities and at reasonable cost are fine-grained sive strength, and erosion/abrasion resistance. The major high-purity alumina (Nextel 610E) and alumina/mullite challenge is to ensure the high temperature stability of the (Nextel 720E) fibers produced by the 3M company. The optimum microstructure. creep, grain growth and strength characteristics of these The earliest work on porous matrix composites used fibers are now well documented [**5,6]. The Nextel 610 silica-based matrices [18], which place a restrictive limit fibers have the higher strengths (|3.3 GPa, cf. 2.1 GPa) on high temperature stability. Recent measurements from a and are expected to be more corrosion resistant in certain composite produced by GEAE (Gen IVE), consisting of environments, whereas the Nextel 720 fibers are more stacked layers of woven alumina fibers (Nextel 610) in an creep resistant and stable to higher temperatures. Based on alumino-silicate matrix, indicate a significant loss in data presently available, the anticipated maximum tem- properties and embrittlement at 9508C [19]. The high peratures for extended use are about 11008C for the Nextel temperature tensile strengths were reduced compared with 610 and 12008C for the Nextel 720 (but dependent on room temperature values by 15 and 50% for unnotched and stress levels and lifetimes). notched test specimens, while observations of fracture A promising approach for improving the creep resist- morphologies indicated a large reduction in the degree of ance of the alumina fibers has been exploited in a new uncorrelated fiber fracture and pullout. Significant notch fiber (Nextel 650E) from 3M [**7]. These fibers contain sensitivity was observed even at room temperature (30% |1% Y O as well as |10% ZrO , based on studies reduction in net-section strength). Large improvements 23 2 showing that doping of grain boundaries in bulk poly- were seen in another alumino-silicate matrix composite crystalline alumina with Y or La leads to large reductions with more stable mullite fibers (Nextel 720), with no effect in creep and grain growth [8]. Improvements were of notches on net section strength at temperatures up to achieved in the creep resistance compared with Nextel 11008C, and small effect at 12008C (|20% reduction) [20]. 610E, although the creep rates remain higher than those of However, under creep conditions the effect of notches was the mullite-containing Nextel 720E fibers. Most of the stronger (|40% reduction in net section strength at properties of the new fibers fall between those of Nextel 11008C) [21], while long-term aging at temperatures of 610E and Nextel 720E. Some interesting questions re- 11008C and above caused significant reductions in room main on the role of the ZrO in changing the properties temperature strengths (60% reduction at 12008C) [22]. 2 and in the relative amounts of Y O in the grain A major advance for porous matrix composites came 2 3 boundaries and in solid solution in the ZrO . with the development of a mullite-based matrix consisting 2 Further increases in temperature capabilities of poly- of relatively large (|1 mm) mullite powder particles, which crystalline oxide fibers are possible with multi-phase are resistant to sintering, forming a continuous network microstructures designed to resist creep and grain growth bonded together with smaller alumina particles (|0.2 mm), or with other systems such as YAG. However, large which sinter more readily [14,15]. Zirconia has also been increases will be difficult, for the fine grain sizes required used as the more readily sintered phase [23]. With a to achieve high strengths lead to relatively rapid creep and processing temperature (12008C) close to the limit of the grain growth. Laboratory-scale fabrication of polycrystal- most refractory oxide fibers presently available (Nextel line mullite fibers with promising, but very preliminary 720), these or related matrix compositions appear to offer property data have been reported [9]. Several groups are the most promising prospects for long-term stability. developing directionally solidified alumina/YAG eutectic Recent high temperature aging experiments with a 2-D fibers, which if they could be produced in small sizes and woven mullite-alumina composite (formed from multiple large quantities would provide very large increases in layers of fabric) [*24] have demonstrated that room-temtemperature capabilities and expand the options for matrix perature tensile properties were not degraded after aging processing [10–13]. for 1000 h at temperatures up to 12008C in air, as shown in Fig. 1. The 0/908 strengths and failure strains were unchanged (Fig. 1), while the 6458 strength, Young’s 3. Weak (porous) matrix composites modulus, and matrix hardness all increased after aging at the highest temperature. The increases indicate that the The effectiveness of the porous matrix concept in mullite/alumina matrix underwent some degree of sinterallowing damage-tolerant composites without the presence ing during the aging period. Under the same conditions, of fiber coatings was previously demonstrated [14,15]. For the previously mentioned alumino-silicate composites sufup-to-date accounts of the design and mechanical prop- fered strength loss of more than 60%
D B. Marshall, J B. Davis /Current Opinion in Solid State and Materials Science 5(2001)28. all the proposed compounds, has attracted the most atten- 39% Nextel 720 fiber Further studies of debonding and sliding at the LaPo Al, O3 interface have confirmed the weak bondi 0, * 31], but have also indicated a possibly important role of plastic deformation in the monazite itself to accommo- date interfacial roughness [31. Both La-monazite and CaWO,(scheelite) have been shown to deform relatively 48% Nextel 720 fiber easily at room temperature by twinning and dislocation motion[ 32]. Connections may exist between unique resistance of monazite to amorphizaton from o00 hour exposure radiation damage, which makes it the prime candidate for long-term storage of actinide wastes 33] 1100 The effectiveness of monazite interface coatings in Heat Treatment Temperature (C) providing a phase-compatible debond layer has now been us matrix composites after high temperature confirmed from tensile strength testing in a variety aging in air(from Ref.[#16 specimen configurations(using uncoated control specimens or comparisons): coatings and coating/matrix combina- tions on individual sapphire fibers [31, 341: individual tows of nextel 610 alumina fibers coated with monazite Detailed measurements are now available for the room and infiltrated with alumina matrix 35]; and unidirectional mperature in-plane tensile properties of a 2-D composi composites of Nextel fibers(610, 650 and 720)with consisting of Nextel 610 fibers(stacked layers of woven monazite coatings and alumina matrix [**36]. In the last fabric)in a porous mullite-alumina matrix(both 0/90 and case the matrix, although porous, was sufficiently strong 45)[*16, 25]. Measurements of notch sensitivity using that very little fragmentation of the matrix took place center-hole tension tests indicate some loss of net -sectio during fracture. Clear evidence was found on the fracture strength in the presence of notches, but much less than for surfaces for the role of the weak interface rather than a a fully notch-sensitive material. Effects of hole size on weak matrix in allowing extensive debonding and pullout strength were rationalized by comparing with stress dis- of fibers. After heat treatment at 1100 and 1200.C, the ributions predicted using non-linear continuum and shear strengths of composites with monazite coatings were all band models: a size-scale dependence in the failur higher than those of the corresponding control specimens, condition is implied. The trends are similar to those the largest differences being seen after 1200.C treatment observed in conventional weak-interface composites (e.g, strength of 200 MPa for coated Nextel 610 composite Systematic studies have now been done to vary the after 5 h at 1200'C compared with 45 MPa for uncrate strength and density of the matrix of the mullite-based control composite composite and measure the effect on the mechanical Although an effective method has been developed for properties [17, *26]. These involved further processing producing thin coatings of monazite on fiber tows(see with multiple cycles of reinfiltration and heat treatment Section 6), a method for coating fibers in a woven fabric using an alumina precursor(Al,(OH)S CI). Bonding of the has not been demonstrated. An approach that circumvents particle network by evaporation-condensation in reactive the need for a separate coating step has been developed on atmosphere has also been used to strengthen the matrix the basis of observations that monazite deposits pref- without decreasing the porosity [23]. As the matrix was erentially between adjacent fibers in tows or fabrics after strengthened and densified there was a trend to increase the infiltration with solution precursors and heat treatment tensile strength in the +45 direction, decrease the strength [ 37]. Infiltration of a slurry consisting of alumina powder in the 0/90 direction, and decrease the degree of uncorre- in a solution precursor for monazite results in a two-phase lated fiber fracture and pullout lengths on the fracture (porous) matrix of alumina and monazite, with a continu- surface ous layer of monazite around all of the fibers. Composites formed by infiltrating fabrics of Nextel 610 and 720 in this manner, followed by stacking, pressing and sintering, have 4. Weak interface developments shown damage-tolerant behavior and absence of notch sensitivity when tested at room temperature and at 1000C Since the discovery that rare-earth phosphates (most (Fig. 2)[37-39]. Although this behavior may be partly notably La-monazite)bond sufficiently weakly with other due to the porous nature of the mati significant oxides to allow debonding of fibers [27], other mixed difference in notch sensitivity is seen between this and the oxide compounds have been proposed and tested for the porous matrix composites described in the previous sec same purpose(tungstates, vanad dates, niobates [9, 28, 29]). tion, thus implying an additional effect of the Nevertheless, La-monazite, which is the most refractory of interface
D.B. Marshall, J.B. Davis / Current Opinion in Solid State and Materials Science 5 (2001) 283–289 285 all the proposed compounds, has attracted the most attention. Further studies of debonding and sliding at the LaPO –4 Al O interface have confirmed the weak bonding 2 3 [30,*31], but have also indicated a possibly important role of plastic deformation in the monazite itself to accommodate interfacial roughness [*31]. Both La-monazite and CaWO (scheelite) have been shown to deform relatively 4 easily at room temperature by twinning and dislocation motion [*32]. Connections may exist between this and the unique resistance of monazite to amorphizaton from radiation damage, which makes it the prime candidate for long-term storage of actinide wastes [33]. The effectiveness of monazite interface coatings in providing a phase-compatible debond layer has now been confirmed from tensile strength testing in a variety of Fig. 1. Strengths of porous matrix composites after high temperature aging in air (from Ref. [**16]). specimen configurations (using uncoated control specimens for comparisons): coatings and coating/matrix combinations on individual sapphire fibers [*31,34]; individual tows of Nextel 610 alumina fibers coated with monazite Detailed measurements are now available for the room and infiltrated with alumina matrix [35]; and unidirectional temperature in-plane tensile properties of a 2-D composite composites of NextelE fibers (610, 650 and 720) with consisting of Nextel 610 fibers (stacked layers of woven monazite coatings and alumina matrix [**36]. In the last fabric) in a porous mullite-alumina matrix (both 0/90 and case the matrix, although porous, was sufficiently strong 458) [**16,*25]. Measurements of notch sensitivity using that very little fragmentation of the matrix took place center-hole tension tests indicate some loss of net-section during fracture. Clear evidence was found on the fracture strength in the presence of notches, but much less than for surfaces for the role of the weak interface rather than a a fully notch-sensitive material. Effects of hole size on weak matrix in allowing extensive debonding and pullout strength were rationalized by comparing with stress dis- of fibers. After heat treatment at 1100 and 12008C, the tributions predicted using non-linear continuum and shear strengths of composites with monazite coatings were all band models: a size-scale dependence in the failure higher than those of the corresponding control specimens, condition is implied. The trends are similar to those the largest differences being seen after 12008C treatment observed in conventional weak-interface composites. (e.g., strength of 200 MPa for coated Nextel 610 composite Systematic studies have now been done to vary the after 5 h at 12008C compared with 45 MPa for uncoated strength and density of the matrix of the mullite-based control composite). composite and measure the effect on the mechanical Although an effective method has been developed for properties [*17,*26]. These involved further processing producing thin coatings of monazite on fiber tows (see with multiple cycles of reinfiltration and heat treatment Section 6), a method for coating fibers in a woven fabric using an alumina precursor (Al (OH) Cl). Bonding of the has not been demonstrated. An approach that circumvents 2 5 particle network by evaporation–condensation in reactive the need for a separate coating step has been developed on atmosphere has also been used to strengthen the matrix the basis of observations that monazite deposits prefwithout decreasing the porosity [23]. As the matrix was erentially between adjacent fibers in tows or fabrics after strengthened and densified there was a trend to increase the infiltration with solution precursors and heat treatment tensile strength in the 6458 direction, decrease the strength [*37]. Infiltration of a slurry consisting of alumina powder in the 0/908 direction, and decrease the degree of uncorre- in a solution precursor for monazite results in a two-phase lated fiber fracture and pullout lengths on the fracture (porous) matrix of alumina and monazite, with a continusurface. ous layer of monazite around all of the fibers. Composites formed by infiltrating fabrics of Nextel 610 and 720 in this manner, followed by stacking, pressing and sintering, have 4. Weak interface developments shown damage-tolerant behavior and absence of notch sensitivity when tested at room temperature and at 10008C Since the discovery that rare-earth phosphates (most (Fig. 2) [*37–39]. Although this behavior may be partly notably La-monazite) bond sufficiently weakly with other due to the porous nature of the matrix, a significant oxides to allow debonding of fibers [27], other mixed difference in notch sensitivity is seen between this and the oxide compounds have been proposed and tested for the porous matrix composites described in the previous secsame purpose (tungstates, vanadates, niobates [9,28,29]). tion, thus implying an additional effect of the weak Nevertheless, La-monazite, which is the most refractory of interface
D B. Marshall, J.B. Davis/ Current Opinion in Solid State and Materials Science 5(2001)283-28 Al2O3 fiber /AL2O3-LaPO4 matrix plumbite with intrinsically weak cleavage planes, analo- gous to mica. These approaches have not proven as effective as either the porous matrix approach or the weakly bonded interface materials described in the previ ous sections [34]. Nevertheless, some useful progress has been made in demonstrating composite properties, refining coating methods, and in defining the relative merits of porosity being concentrated at an interface or distributed 50英z 瞿 throughout the matrix Porous interphases are most commonly produced by 100 mixing fugitive carbon with the fiber coating material ●1100°c/1h; Room Temp Zirconia. rare-earth aluminates. and zircon have been 1100°c/24h; Room Temp investigated recently [45-48]. Composites have been ■1100c/1h;1025 C Test produced by hot pressing sapphire fibers with porous zirconia coatings in an alumina matrix [45, 46]. Althor the composites had relatively low strengths (-100-130 MPa for 0/90 cross-ply ) they were not degraded after ycling at 1200C (1300 cycles)and aging at tempera- Fig. 2. Effect of notch depth and heat-treatment conditions on net-section rengths measured at room temperature and at 1025C. Monazite/ tures that would severely degrade composites with poly umina matrix, Nextel"610 fibers. Specimen width: w=13 mm. crystalline oxide fibers (100 h at 1400C Several groups have produced composites with a thin continuous gap between the fibers and matrix by using a Several studies have shown that infiltration of Nextel fugitive carbon coating on the fibers [49-52]. Useful fiber tows and fabrics with solution precursors, followed insight into the merit of the approach is provided in Ref. by heat treatment to form monazite, often leads to strength [491, where comparisons with uncoated control specimens degradation [40-**44]. Many combinations of precu indicated that the gap was effective in enabling fiber chemistry, fiber composition, temperature, and time have pullout in composites of Nextel 720 fibers in a dense been assessed, with strength measurements being obtained calcium alumino-silicate(CAS)matrix, whereas the gap both from individual fibers with thin monazite coatings of had no effect composite with a porous matrix of 100 nm thickness(see Section 6 for coating method) mullite-alumina. Although the starting strengths were low [*42-**44 and from infiltrated fiber tows that form in this study (130 MPa), there was no degradation in the mini-composites [40, **41]. Although the detailed mecha- porous matrix composite after 500 h at 1150C and a smal nisms of degradation in most cases are not known, it is loss(-20%)in the CAs matrix composite after aging for clear that the mechanisms involve the precursor chemistry 500 h at 1000C rather than the monazite itself, since degradation does not The use of layered crystal structures presents several occur with coatings formed from aqueous slurries of challenges:(1) to form the desired phase at a rhabdophane particles (hydrated monazite) and in low temperature that the fibers are not degraded during minicomposites formed by infiltration with slurries of processing; (ii) to orient the weak basal planes of the monazite particles. Indeed, in these cases the strengths crystals parallel to the fiber surface; and (iii) to control the after heat treatment are often higher than strengths of roughness of the fracture in the coating to allow con- uncoated control specimens. Strength loss is also avoided strained sliding of the fibers. Progress has been made in in some cases when fiber tows are infiltrated with slurries lowering the formation temperature for refractory hexa- consisting of alumina particles in solution precursors described above, possibly a result of the alumina acting as techniques [53-57. However, although textured coatings internal buffer. Many observations are consistent with a have been grown on single-crystal YAG plates at 1200C, hypothesis that trapped gases remaining from the pre- there is a suggestion that on polycrystalline alumina fibers (Nextel 610) there may not be an adequate driving forc during heat treatment and react with the fiber surface for grain growth and texturing at this temperature(which the limit to which these fibers may be exposed during 5. Layered and porous interphases 6. Fiber coating methods Some of the earliest attempts to produce damage-toler nt oxide composites were based on forming weak fiber Although chemical and physical vapor methods have coatings,either by the introduction of porosity or by use of been used to deposit coatings of monazites and hexalumi- layered crystal structures such as B-alumina/magneto- nates [29], the deposition of stoichiometric multicom
286 D.B. Marshall, J.B. Davis / Current Opinion in Solid State and Materials Science 5 (2001) 283–289 plumbites with intrinsically weak cleavage planes, analogous to mica. These approaches have not proven as effective as either the porous matrix approach or the weakly bonded interface materials described in the previous sections [34]. Nevertheless, some useful progress has been made in demonstrating composite properties, refining coating methods, and in defining the relative merits of porosity being concentrated at an interface or distributed throughout the matrix. Porous interphases are most commonly produced by mixing fugitive carbon with the fiber coating material. Zirconia, rare-earth aluminates, and zircon have been investigated recently [*45–48]. Composites have been produced by hot pressing sapphire fibers with porous zirconia coatings in an alumina matrix [*45,46]. Although the composites had relatively low strengths (|100–130 MPa for 0/90 cross-ply), they were not degraded after cycling at 12008C (.1300 cycles) and aging at temperaFig. 2. Effect of notch depth and heat-treatment conditions on net-section tures that would severely degrade composites with poly- strengths measured at room temperature and at 10258C. Monazite/ crystalline oxide fibers (100 h at 14008C). alumina matrix, NextelE 610 fibers. Specimen width: w513 mm. Several groups have produced composites with a thin continuous gap between the fibers and matrix by using a Several studies have shown that infiltration of Nextel fugitive carbon coating on the fibers [*49–52]. Useful fiber tows and fabrics with solution precursors, followed insight into the merit of the approach is provided in Ref. by heat treatment to form monazite, often leads to strength [*49], where comparisons with uncoated control specimens degradation [40–**44]. Many combinations of precursor indicated that the gap was effective in enabling fiber chemistry, fiber composition, temperature, and time have pullout in composites of Nextel 720 fibers in a dense been assessed, with strength measurements being obtained calcium alumino-silicate (CAS) matrix, whereas the gap both from individual fibers with thin monazite coatings of had no effect in a composite with a porous matrix of |100 nm thickness (see Section 6 for coating method) mullite-alumina. Although the starting strengths were low [**42–**44] and from infiltrated fiber tows that form in this study (|130 MPa), there was no degradation in the mini-composites [40,**41]. Although the detailed mecha- porous matrix composite after 500 h at 11508C and a small nisms of degradation in most cases are not known, it is loss (|20%) in the CAS matrix composite after aging for clear that the mechanisms involve the precursor chemistry 500 h at 10008C. rather than the monazite itself, since degradation does not The use of layered crystal structures presents several occur with coatings formed from aqueous slurries of challenges: (i) to form the desired phase at a sufficiently rhabdophane particles (hydrated monazite) and in low temperature that the fibers are not degraded during minicomposites formed by infiltration with slurries of processing; (ii) to orient the weak basal planes of the monazite particles. Indeed, in these cases the strengths crystals parallel to the fiber surface; and (iii) to control the after heat treatment are often higher than strengths of roughness of the fracture in the coating to allow conuncoated control specimens. Strength loss is also avoided strained sliding of the fibers. Progress has been made in in some cases when fiber tows are infiltrated with slurries lowering the formation temperature for refractory hexaconsisting of alumina particles in solution precursors as luminates as low as 10008C using sol–gel and doping described above, possibly a result of the alumina acting as techniques [*53–57]. However, although textured coatings an internal buffer. Many observations are consistent with a have been grown on single-crystal YAG plates at 12008C, hypothesis that trapped gases remaining from the pre- there is a suggestion that on polycrystalline alumina fibers cursors can build up high pressures in dense coatings (Nextel 610) there may not be an adequate driving force during heat treatment and react with the fiber surface for grain growth and texturing at this temperature (which is [**44]. the limit to which these fibers may be exposed during processing) [*53]. 5. Layered and porous interphases 6. Fiber coating methods Some of the earliest attempts to produce damage-tolerant oxide composites were based on forming weak fiber Although chemical and physical vapor methods have coatings, either by the introduction of porosity or by use of been used to deposit coatings of monazites and hexalumilayered crystal structures such as b-alumina/magneto- nates [29], the deposition of stoichiometric multicom-
D B. Marshall, J B. Davis/ Current Opinion in Solid State and Materials Science 5(2001)283-289 287 ponent oxide coatings by such methods is difficult. Solu- References tion precursor, sol-gel, or slurry methods potentially allow better control of stoichiometry, although it is more difficult Papers of particular interest, published within the annual to obtain uniform bridge-free coatings on individual fibers period of review, have been highlighted in tows or woven preforms s of special interest A technique that minimizes the bridging problem in- ** of outstanding interest volves passing the fiber tows through a coating solution or slurry covered with a layer of immiscible liquid that [1] Robinson RC, Smialek JL. SiC recession caused by SiO, scale displaces excess coating solution from between the fibers volatility under combustion conditions: I. Experimental results as they are withdrawn [58]. This method has proven nd empirical model. J Am Ceram Soc 1999: 82: 1817-25 effective for depositing thin coatings of monazite(=50- 2]Opila EJ, Smialek JL, Robinson RC, Fox DS, Jacobson NS. Sic 100 nm thickness ) on Nextel 610 and 720 fiber tows using caused by SiO, scale volatility under combustion conditions: Il. Thermodynamics and gaseous diffusion model. J a variety of different solution precursors and slurries Am Ceram Soc1999;82:1826-34 [42-44].It has also been used to deposit po 3]Cox BN, Zok Fw. Advances in ceramic composites reinforced by coatings using a fugitive carbon phase (La-hexaluminate, ontinuous fibers. Curr Opin Solid State Mater Sci 1996: 1: 666- YAG and zircon)[47, 48 14 Evans AG, Marshall DB, Zok F, Levi C. Recent advances in 7. Matrix processing methods 1999;8:17-23. [*5 Hay Rs, Boakeye E, Petry MD, Berta Y, Von Lehmden K, Welch J. Grain growth and tensile strength of 3-M Nextel 720TM after The composites described above were processed using a thermal exposure. Ceram Eng Sci Proc 1999, 20: 165-72, Tensile riety of liquid-based infiltration methods(slurry, sol-gel rength and grain growth of 3M Nextel 720 fibers measured recursor) to infiltrate the matrix material into fiber tows after heat-treatment from 1000 to 1500C for 20 min to 300 h woven fabrics at, or near room temperature, followed by Possible mechanisms for strength degradation are discussed sintering to strengthen the matrix. a challenge remains to [6]Petry MD, Mah T. Effect of thermal exposures on the strengths of extel 550 and 720 filaments. J Am Ceram Soc 1999: 82: 2801-7 develop more versatile methods capable of infiltrating high More strength and grain growth data for Nextel 720 and Nextel volume fractions of matrix into fiber preforms. An innova- 550 as a function of aging temperature and environment, with and tive method was described in Ref [23] for producing tapes ithout carbon coatings with very high particle packing and shear thinning charac u*7 Wilson DM, Visser LR. Nextel 650 ceramic oxide fiber. New teristics that allow infiltration by simple stacking of fabrics alumina-based fiber for high temperature composite rein- forcement. Ceram Eng Sci Proc 2000: 21: 363-73, Properties of and tapes followed by application of shear displacements new polycrystalline alumina fiber doped with Y2 O, and ZrO,to by vibration aprove microstructural stability and creep resistance. [8] Bruley J, Cho J, Chan HM, Harmer MP, Rickman JM. Scanning ansmission electron microscopy analysis of grain boundaries in 8. Conclusions creep-resistant yttrium- and lanthanum-doped alumina microstruc tures. J Am Ceram Soc 1999: 81: 2865-70. Several types of oxide composite now appear capable 9 Lewis MH, York S, Freeman C, Alexander IC, Al-Dawery 1 providing sustained use at temperatures as high as 1200C. butler EG, Doleman PA Oxide CMCs, novel fibres, coatings and abrication procedures. Ceram Eng Sci Proc 2000,21: 535-47 While considerable testing in combustion environments Laboratory scale polycrystalline mullite fibers with very prelimin- with realistic gas flow rates and compositions is still ry property measurement. Compatibility tests of LaPO, NdPO needed to prove their viability, and further improvements and Lavo, interphases in properties and processing methods are desirable, there is [10 Mah Tl, Parthasarathy TA, Kerans R, Processing, microstructure now an opportunity to explore innovative combustion and strength of Alumina-YAG eutectic polycrystals. J Am Ceram Soc2000;83:2088-90 component designs that avoid limitations of metallic [11] Sayir A editor, Directional Solidification of eutectic ceramics. In: ystems. Applications of monazite-based composites Pechenik A, Kalia RK, Vashita P, editors. Computer Aided Desig thermal protection systems for space re-entry vehicles are of High-Temperature Materials, New York: Oxford University already progressing rapidly in this direction [**41]. Sub- Press. 1999 component testing in wind tunnel, arc jet, and impact [12] Yoshikawa A, Epelbaum BM, Fukuda T, Suzuki K, Waku Y. environments at temperatures up to 1300.C, have shown rowth of Al203/Y3A15o12 eutectic fiber by micro-pulling down method and its high temperature strength and thermal large gains compared with conventional silica-based sys- bility. Jpn J Appl Phys 1999, 38: 55-8 [13 Yoshikawa A, Haseg Fukuda T. Suzuki K. Waku Growth and diameter control of Al2031Y3A15012 eutectic fiber by micro-pulling-down method and its high temperature strength Acknowledgements d thermal stability. Ceram Eng Sci Proc 1999: 20:275-82. [14 Lange FF, Tu w-C, Evans AG. Processing of damage-tolerant, oxidation-resistant ceramic-matrix composites by a precur Financial support was supplied by the Us Air Force infiltration and pyrolysis method. Mater Sci Eng 1995; A195: 145- Office of Scientific Research. contract No. F49620-00-C [15] Levi CG, Yang JY, Dalgleish BJ, Zok FW, Evans AG. Processing
D.B. Marshall, J.B. Davis / Current Opinion in Solid State and Materials Science 5 (2001) 283–289 287 ponent oxide coatings by such methods is difficult. Solu- References tion precursor, sol–gel, or slurry methods potentially allow better control of stoichiometry, although it is more difficult Papers of particular interest, published within the annual to obtain uniform bridge-free coatings on individual fibers period of review, have been highlighted as: in tows or woven preforms. * of special interest; A technique that minimizes the bridging problem in- ** of outstanding interest. volves passing the fiber tows through a coating solution or slurry covered with a layer of immiscible liquid that [1] Robinson RC, Smialek JL. SiC recession caused by SiO scale 2 displaces excess coating solution from between the fibers volatility under combustion conditions: I. Experimental results and empirical model. J Am Ceram Soc 1999;82:1817–25. as they are withdrawn [58]. This method has proven [2] Opila EJ, Smialek JL, Robinson RC, Fox DS, Jacobson NS. SiC effective for depositing thin coatings of monazite (|50– recession caused by SiO scale volatility under combustion 2 100 nm thickness) on Nextel 610 and 720 fiber tows using conditions: II. Thermodynamics and gaseous diffusion model. J a variety of different solution precursors and slurries Am Ceram Soc 1999;82:1826–34. [**42–**44]. It has also been used to deposit porous [3] Cox BN, Zok FW. Advances in ceramic composites reinforced by coatings using a fugitive carbon phase (La-hexaluminate, continuous fibers. Curr Opin Solid State Mater Sci 1996;1:666– 73. YAG and zircon) [47,48]. [4] Evans AG, Marshall DB, Zok F, Levi C. Recent advances in oxide-oxide composite technology. Adv Composite Mater 1999;8:17–23. 7. Matrix processing methods [**5] Hay RS, Boakeye E, Petry MD, Berta Y, Von Lehmden K, Welch J. Grain growth and tensile strength of 3-M Nextel 720TM after The composites described above were processed using a thermal exposure. Ceram Eng Sci Proc 1999;20:165–72, Tensile variety of liquid-based infiltration methods (slurry, sol–gel, strength and grain growth of 3M Nextel 720E fibers measured after heat-treatment from 1000 to 15008C for 20 min to 300 h. precursor) to infiltrate the matrix material into fiber tows or Possible mechanisms for strength degradation are discussed. woven fabrics at, or near room temperature, followed by [6] Petry MD, Mah T. Effect of thermal exposures on the strengths of sintering to strengthen the matrix. A challenge remains to Nextel 550 and 720 filaments. J Am Ceram Soc 1999;82:2801–7, develop more versatile methods capable of infiltrating high More strength and grain growth data for Nextel 720 and Nextel volume fractions of matrix into fiber preforms. An innova- 550 as a function of aging temperature and environment, with and without carbon coatings. tive method was described in Ref. [23] for producing tapes [**7] Wilson DM, Visser LR. Nextel 650 ceramic oxide fiber. New with very high particle packing and shear thinning charac- alumina-based fiber for high temperature composite rein- teristics that allow infiltration by simple stacking of fabrics forcement. Ceram Eng Sci Proc 2000;21:363–73, Properties of and tapes followed by application of shear displacements new polycrystalline alumina fiber doped with Y O and ZrO to 23 2 by vibration. improve microstructural stability and creep resistance. [8] Bruley J, Cho J, Chan HM, Harmer MP, Rickman JM. Scanning transmission electron microscopy analysis of grain boundaries in 8. Conclusions creep-resistant yttrium- and lanthanum-doped alumina microstructures. J Am Ceram Soc 1999;81:2865–70. [9] Lewis MH, York S, Freeman C, Alexander IC, Al-Dawery I, Several types of oxide composite now appear capable of butler EG, Doleman PA. Oxide CMCs, novel fibres, coatings and providing sustained use at temperatures as high as 12008C. fabrication procedures. Ceram Eng Sci Proc 2000;21:535–47, While considerable testing in combustion environments Laboratory scale polycrystalline mullite fibers with very preliminwith realistic gas flow rates and compositions is still ary property measurement. Compatibility tests of LaPO , NdPO 4 4 and LaVO interphases. needed to prove their viability, and further improvements 4 [10] Mah TI, Parthasarathy TA, Kerans RJ. Processing, microstructure, in properties and processing methods are desirable, there is and strength of Alumina-YAG eutectic polycrystals. J Am Ceram now an opportunity to explore innovative combustion Soc 2000;83:2088–90. component designs that avoid limitations of metallic [11] Sayir A. editor, Directional Solidification of eutectic ceramics. In: systems. Applications of monazite-based composites in Pechenik A, Kalia RK, Vashita P, editors. Computer Aided Design thermal protection systems for space re-entry vehicles are of High-Temperature Materials, New York: Oxford University Press, 1999: 197–211. already progressing rapidly in this direction [**41]. Sub- [12] Yoshikawa A, Epelbaum BM, Fukuda T, Suzuki K, Waku Y. component testing in wind tunnel, arc jet, and impact Growth of Al2O3/Y3Al5O12 eutectic fiber by micro-pulling- environments at temperatures up to 13008C, have shown down method and its high temperature strength and thermal large gains compared with conventional silica-based sys- stability. Jpn J Appl Phys 1999;38:L55–8. tems. [13] Yoshikawa A, Hasegawa K, Fukuda T, Suzuki K, Waku Y. Growth and diameter control of Al2O31Y3Al5012 eutectic fiber by micro-pulling-down method and its high temperature strength Acknowledgements and thermal stability. Ceram Eng Sci Proc 1999;20:275–82. [14] Lange FF, Tu W-C, Evans AG. Processing of damage-tolerant, oxidation-resistant ceramic-matrix composites by a precursor Financial support was supplied by the US Air Force infiltration and pyrolysis method. Mater Sci Eng 1995;A195:145– Office of Scientific Research, contract No. F49620-00-C- 50. 0010. [15] Levi CG, Yang JY, Dalgleish BJ, Zok FW, Evans AG. Processing
88 D B. Marshall, J.B. Davis Current Opinion in Solid State and Materials Science 5(2001)283-20 d performance of an all-oxide ceramic composite. J Am Ceram site (mullite alumina) with systematically varied density and Socl998;81:2077-86 strength of the matrix L*16 Zok Fw, Levi CG. Mechanical es of porous-matrix [27 Morgan PED, Marshall DB. Ceramic composites of monazite and omposites. Adv Eng Mater 2001; 3: 15-23, Review of porous lumina. J Am Ceram Soc 1995: 78: 1553-63 posites, covering mechanics considerations in th [28]Goettler RW, Sambasivan S, Dravid V, Kim S Interfaces in oxide fiber- oxide matrix ceramic composites. In: Pechenik A, Kalia rties under tensile loading in various directions as well as in RH, Vashita P, eds Computer Aided Design of sence of notches and holes, and assessment of prospects for Materials, New York: Oxford University Press, 1999: 333-349 CawO, ErTaO, interphases: strengths of Scheelite-coated [17 Levi ok FW, Yang JY, Mattoni M, Lofvander JPA N6100 fibers after 1100C/1 h-no strength loss. howeve Microstructural design of stable po matrices for strength loss in comp made with Al, O, polymer ceramic composites. Z Metallkde 1999: 90: 1037-47, The princi- [29] Lewis MH, Tye A, Butler EG, Doleman PA. Oxide CMCs les guiding the microstructural design of porous matrix compos thesis and novel fibre development. J Eur Ceram ites using two particulate oxide constituents, in different size Soc 2000, 20: 639-44, Deposition of rare-earth vanadates and scales and with distinctly different sintering kinetic hosphate from colloidal precursors or by magnetron sputterin Thermal stability with reference to al fibres and matrice recursor(Al, (OH)s CI) on microstructure and tensile 30] Marshall DB, Waldrop JR, Morgan PED. Thermal grooving at the described monazite. Acta Mate [18 Harrison MG, Millard ML, Szweda A. Fiber Reinforced Ceramic 2000: 48: 4471-4, Atomic force microscopy of monazite alumina Matrix ce te Member and method for Making. US Patent interface fracture surfaces No.5306554; UK Patent No.2230259(1994 [31 Marshall DB, Davis JB, Morgan PED, Waldrop JR, Porter JP [19]Kramb VA, John R, Zawada LP Notched fracture behavior of an Properties of La-monazite as an interphase in oxide composites. Z oxide/oxide ceramic-matrix composite. J Am Ceram Soc Metallkde 1999: 90: 1048-52, Room temperature deformation of 1999: 82: 3087-96, Tensile test data from Gen IV(N610) at room onazite at rough sliding interfaces. temperature and 950"C: shows some notch sensitivity at RT(66% [32 Hay Rs Monazite and scheelite deformation mechanisms. Ceram net section strength) and large notch sensitivity at 950C(30% net Eng Sci Proc 2000: 21: 203-28, TEM observations showing dislo- ection strength ). Observations of damage from fracture surfaces cations and twins in materials deformed at room temperature nd polished sections indicate embrittlement at 950C [33] Meldrum A, Boatner LA, Ewing RC. A comparison of radiation [20 Buchanan DJ, John R, Zawada LP. Notched fracture behavior of effects in crystalline ABO4 type phosphates and silicates. Mineral xide-oxide Nextel 720/As composite. Ceram Eng Sci Proc Mag 2000: 64: 185-94, Radiation damage was monitored 2000: 21: 567-74, Tensile test data showing no effect of notches function of temperature in situ in a transmission electron micro- on net section strength of Nextel 710/alumino-silicate matrix ope. The critical temperature, above which the recrystallization omposite at temperatures up to 1100.C, and small effect at processes are faster than damage accumulation and amorphization 1200.C (-20% reduction). annot be induced, was only 35C for LaPO4, much lower than [21] John R, Buchanan DJ, Zawada LP. Creep deformation and ruptur for other phosphates and silicates behavior of a notched oxide-oxide Nextel 720/As composite. [34] Parthasarathy TA, Boakeye E, Cinibulk MK, Perry MD. Fabrica- Ceram Eng Sci Proc 2000: 21: 567-74, Tensile creep data from the tion and testing of oxide/oxide microcomposites with monazite same composites as in Ref. 20). and hibonite as interlayers. J Am Ceram Soc 1999: 82: 3575-83 [22] Jurf RA, Butner SC. Advances in oxide-oxide CMC J Eng Gas Strengths of single fiber composites: sapphire+LaPO, +10 ur Turbines Power 2000: 122: 202-5. Tensile strengths lextel Al,O, Also hibonite(CaAln,g) 710/alumino-silicate matrix composite after long-term aging at 35] Keller KA, Mah T-L, Boakye EE, Parthasarathy TA Gel-casting temperatures up to 1200.C nd reaction bonding of oxide-oxide minicomposites with mona [23] Haslam JJ, Berroth KE, Lange FF. Processing and properties of zite interphase. Ceram Eng Sci Proc 2000, 21: 525-34 n all-oxide composite with a porous matrix J Eur Ceram Soc [*36 Keller KA, Mah T, Parthasarathy TA, Boakye EE, Cinibulk M. 2000: 20: 607-18, Formation of mullite-zirconia matrix composite Evaluation of all-oxide composites based on coated Nextel 610 using a vibro- impregnation process with tape freezing followed and 650 fibers. Ceramic Engineering and Science Proceedings by sintering without shrinkage in a reactive atmosphere 2001, in press. Unidirectional composites of Nextel fibers(610, [24] Carelli E, Fujita H, Yang J, Zok Fw. On the mechanical properties 650 and 720) with monazite coatings and alumina matrix: after of a porous-matrix ceramic composite following thermal aging, J heat treatments at 1100 and 1200C, the strengths of composites Am. Ceram. Soc. (in press). Effect of long-term aging at with monazite coatings were all higher than those of the core. temperatures up to 1200"C on properties of Nextel 720/mullite sponding control specimens, the largest differences being seen lumina matrix composite after 1200.C treatment (e.g, 200 MPa for coated Nextel 610 [25 Heathcote JA, Gong XY, Yang JY, Ramamurty U, Zok Fw omposite after 5 h at 1200C, 45 MPa for uncoated control J Am Ceram Soc 1999: 82. 2721-30. Detailed measurements of [37] Davis JB, Marshall DB, Morgan PED. Monazite containing room temperature tensile properties of 2-D composite consisting oxide-oxide composites. J Eur Ceram Soc 2000: 20:583-7, Prop- of Nextel 610 fibers in porous mullite- alumina matrix(both 0/90 erties of composite formed by infiltrating Nextel" 610 fibe nd 45). Notch sensitivity is assessed using center-hole tension preform with slurry of alumina in solution precursor for monazite tests: some loss of strength is observed in the presence of notches. *38] Davis JB, Marshall DB, Morgan PED. Oxide composites o but much less than for a fully notch sensitive material. Effects o AlO and LaPO. J Eur Ceram Soc 1999 19: 2421-6. Fracture ole size on strength were rationalized by comparing with stres servations from composite formed by infiltrating NextelTM 610 tributions predicted using non-linear continuum and shear band fiber preform with slurry of alumina in solution precursor for monazite and from composite with sapphire fibers and fully dense [26] Mattoni M, Yang JY, Levi CG, Zok Fw. Effects of a precursor. monazite matrIx derived alumina on the mechanical properties of a porous matrix, [39] Morgan PED, Marshall DB, Davis JB, Housley RM. The weak all-oxide ceramic composite, Mater. Sci. Eng.(2000)in press interface between monazites and refractory ceramic oxides. In Measurements of changes in properties of porous matrix compo- Pechenik A, Kalia RK Vashishta P, eds Computer Aided Design
288 D.B. Marshall, J.B. Davis / Current Opinion in Solid State and Materials Science 5 (2001) 283–289 and performance of an all-oxide ceramic composite. J Am Ceram site (mullite alumina) with systematically varied density and Soc 1998;81:2077–86. strength of the matrix. [**16] Zok FW, Levi CG. Mechanical properties of porous-matrix [27] Morgan PED, Marshall DB. Ceramic composites of monazite and composites. Adv Eng Mater 2001;3:15–23, Review of porous alumina. J Am Ceram Soc 1995;78:1553–63. matrix composites, covering mechanics considerations in the [28] Goettler RW, Sambasivan S, Dravid V, Kim S. Interfaces in oxide design of the composite microstructures, a survey of mechanical fiber — oxide matrix ceramic composites. In: Pechenik A, Kalia properties under tensile loading in various directions as well as in RH, Vashita P, eds. Computer Aided Design of High-Temperature the presence of notches and holes, and assessment of prospects for Materials, New York: Oxford University Press, 1999: 333–349. long-term stability. CaWO & ErTaO interphases: strengths of Scheelite-coated 4 4 [*17] Levi CG, Zok FW, Yang JY, Mattoni M, Lofvander JPA. N6100 fibers after 11008C/1 h — no strength loss. However Microstructural design of stable porous matrices for all-oxide strength loss in composites made with Al O polymer 2 3 ceramic composites. Z Metallkde 1999;90:1037–47, The princi- [29] Lewis MH, Tye A, Butler EG, Doleman PA. Oxide CMCs: ples guiding the microstructural design of porous matrix compos- interphase synthesis and novel fibre development. J Eur Ceram ites using two particulate oxide constituents, in different size Soc 2000;20:639–44, Deposition of rare-earth vanadates and scales and with distinctly different sintering kinetics are are phosphates from colloidal precursors or by magnetron sputtering. reviewed. The effects of multiple reinfiltration with an alumina Thermal stability with reference to potential fibres and matrices. precursor (Al (OH) Cl) on microstructure and tensile properties 2 5 [30] Marshall DB, Waldrop JR, Morgan PED. Thermal grooving at the are described. interface between alumina and monazite. Acta Mater [18] Harrison MG, Millard ML, Szweda A. Fiber Reinforced Ceramic 2000;48:4471–4, Atomic force microscopy of monazite alumina Matrix Composite Member and method for Making. US Patent interface fracture surfaces. No. 5 306 554; UK Patent No. 2 230 259 (1994). [*31] Marshall DB, Davis JB, Morgan PED, Waldrop JR, Porter JP. [19] Kramb VA, John R, Zawada LP. Notched fracture behavior of an Properties of La-monazite as an interphase in oxide composites. Z oxide/oxide ceramic-matrix composite. J Am Ceram Soc Metallkde 1999;90:1048–52, Room temperature deformation of 1999;82:3087–96, Tensile test data from Gen IV (N610) at room monazite at rough sliding interfaces. temperature and 9508C: shows some notch sensitivity at RT (66% [*32] Hay RS. Monazite and scheelite deformation mechanisms. Ceram net section strength) and large notch sensitivity at 9508C (30% net Eng Sci Proc 2000;21:203–28, TEM observations showing dislosection strength). Observations of damage from fracture surfaces cations and twins in materials deformed at room temperature. and polished sections indicate embrittlement at 9508C. [33] Meldrum A, Boatner LA, Ewing RC. A comparison of radiation [20] Buchanan DJ, John R, Zawada LP. Notched fracture behavior of effects in crystalline ABO -type phosphates and silicates. Mineral 4 oxide-oxide Nextel 720/AS composite. Ceram Eng Sci Proc Mag 2000;64:185–94, Radiation damage was monitored as a 2000;21:567–74, Tensile test data showing no effect of notches function of temperature in situ in a transmission electron microon net section strength of Nextel 710/alumino-silicate matrix scope. The critical temperature, above which the recrystallization composite at temperatures up to 11008C, and small effect at processes are faster than damage accumulation and amorphization 12008C (|20% reduction). cannot be induced, was only 358C for LaPO , much lower than 4 [21] John R, Buchanan DJ, Zawada LP. Creep deformation and rupture for other phosphates and silicates. behavior of a notched oxide-oxide Nextel 720/AS composite. [34] Parthasarathy TA, Boakeye E, Cinibulk MK, Perry MD. FabricaCeram Eng Sci Proc 2000;21:567–74, Tensile creep data from the tion and testing of oxide/oxide microcomposites with monazite same composites as in Ref. [20]. and hibonite as interlayers. J Am Ceram Soc 1999;82:3575–83, [22] Jurf RA, Butner SC. Advances in oxide-oxide CMC. J Eng Gas Strengths of single fiber composites: sapphire1LaPO4110 mm Turbines Power 2000;122:202–5, Tensile strengths of Nextel Al O Also hibonite (CaAl O ). 2 3 12 19 710/alumino-silicate matrix composite after long-term aging at [35] Keller KA, Mah T-I, Boakye EE, Parthasarathy TA. Gel-casting temperatures up to 12008C. and reaction bonding of oxide-oxide minicomposites with mona- [23] Haslam JJ, Berroth KE, Lange FF. Processing and properties of zite interphase. Ceram Eng Sci Proc 2000;21:525–34. an all-oxide composite with a porous matrix. J Eur Ceram Soc [**36] Keller KA, Mah T, Parthasarathy TA, Boakye EE, Cinibulk M. 2000;20:607–18, Formation of mullite-zirconia matrix composite Evaluation of all-oxide composites based on coated Nextel 610 using a vibro-impregnation process with tape freezing followed and 650 fibers. Ceramic Engineering and Science Proceedings by sintering without shrinkage in a reactive atmosphere. 2001, in press. Unidirectional composites of NextelE fibers (610, [*24] Carelli E, Fujita H, Yang J, Zok FW. On the mechanical properties 650 and 720) with monazite coatings and alumina matrix: after of a porous-matrix ceramic composite following thermal aging, J. heat treatments at 1100 and 12008C, the strengths of composites Am. Ceram. Soc. (in press). Effect of long-term aging at with monazite coatings were all higher than those of the corretemperatures up to 12008C on properties of Nextel 720/mullite- sponding control specimens, the largest differences being seen alumina matrix composite. after 12008C treatment (e.g., 200 MPa for coated Nextel 610 [*25] Heathcote JA, Gong XY, Yang JY, Ramamurty U, Zok FW. composite after 5 h at 12008C, 45 MPa for uncoated control In-plane mechanical properties of an all-oxide ceramic composite. composite). J Am Ceram Soc 1999;82:2721–30, Detailed measurements of [*37] Davis JB, Marshall DB, Morgan PED. Monazite containing room temperature tensile properties of 2-D composite consisting oxide-oxide composites. J Eur Ceram Soc 2000;20:583–7, Propof Nextel 610 fibers in porous mullite-alumina matrix (both 0/90 erties of composite formed by infiltrating NextelE 610 fiber and 458). Notch sensitivity is assessed using center-hole tension preform with slurry of alumina in solution precursor for monazite. tests: some loss of strength is observed in the presence of notches, [*38] Davis JB, Marshall DB, Morgan PED. Oxide composites of but much less than for a fully notch sensitive material. Effects of Al O and LaPO . J Eur Ceram Soc 1999;19:2421–6, Fracture 23 4 hole size on strength were rationalized by comparing with stress observations from composite formed by infiltrating NextelTM 610 distributions predicted using non-linear continuum and shear band fiber preform with slurry of alumina in solution precursor for models. monazite and from composite with sapphire fibers and fully dense [*26] Mattoni M, Yang JY, Levi CG, Zok FW. Effects of a precursor- monazite matrix. derived alumina on the mechanical properties of a porous-matrix, [39] Morgan PED, Marshall DB, Davis JB, Housley RM. The weak all-oxide ceramic composite, Mater. Sci. Eng. (2000) in press. interface between monazites and refractory ceramic oxides. In: Measurements of changes in properties of porous matrix compo- Pechenik A, Kalia RK Vashishta P, eds. Computer Aided Design
D B. Marshall, J.B. Davis Current Opinion in Solid State and Materials Science 5(2001)283-20 of High-Temperature Materials, New York: Oxford University YAG with fugitive carbon phase and with black glass matrix. Press,1999:229-243. La-hexaluminate coatings degrade tow strengths(40%) but help 140 Davis JB, Marshall DB, Oka Ks, Housley RH, MorgaN otect the fibers from reaction with the matrix. YAg coatings die Ceramic composites for thermal protection systems. Composites: Part A1999;30:483-8 [48] Boakye E, Hay RS, Petry MD, Parthasarathy TA. Sol-gel [*41 Davis JB, Marshall DB, Morgan PED, Oka Ks, Barney AO, thesis of zircon-carbon precursors and of Nextel Hogenson PA. Damage tolerant thermal protection systems, in 720TM fiber tows. Ceram Eng Sci Proc 65-72,A Proc Space 2000, American Institute of Aeronautics and As- ircon-carbon precursor was continuously tronautics, Long Beach, CA, 2000. Infiltration and heat treatmen 720TM fibers using a sol-gel method. Zircon formation was f fiber tows and fabrics with monazite slurries and solution tarded by the presence of carbon. recursors. Strength degradation observed for solution precursor [49 Keller KA, Mah Tl, Parthasarathy TA et al. Fugitive interfacial atings for oxide/oxide composites. J Am Ceram Soc arries of monazite powder, giving 53: 329-36, Comparison of effect of interface gap in com monazite matrix. Retained strengths =: with dense and porous matrices [50] Peters PWM, Daniels B, Clemens F et al. Mechanical characteri- 442] Boakye E, Hay RS, Petry MD Continuous coating of oxide fiber ation of mullite-based ceramic matrix composites at test tem tows using liquid precursors: monazite coatings on Nextel 720. J up to 1200C. J Eur Ceram Soc 2000: 20: 53 1-5, Nextel 610 Ceram Soc 1999: 82- 2321-31. Seven different fibre-reinforced mullite-based matrix with a 0. 1-Hm thick carbon ethanolic precursors were used to coat monazite on Nextel 720 oating on fibers. Tensile strength decreased rapidly at tempera- fiber tows using the immiscible liquid displacement method to minimize bridging of coating between filaments. Coatings were [ Halverson HG, Curtin WA pture of Nextel 610/alumina cured in-line at 1200-1400C. Tensile strengths measured from yttria composites. Ceram Eng Sci Proc 2000: 21:559-66, HT individual coated fibers showed significant degradation. strength, stress-rupture, and creep of composite with porous [] Hay Rs, Boakye E, Petry MD. Effect of coating deposition natrix/interface: large decreases in rupture stress at 1050"C mperature on monazite coated fiber. J Eur Ceram Soc [52] Mackin TJ, Roberts MC. Evaluation of damage evolution in 2000: 20: 589-97, Further studies as in previous reference and ceramic-matrix composites using thermoelastic stress analysis microstructural analysis. Tensile strengths of coated fibers de Am Ceram Soc 2000: 83: 337-43, Thermoelastic stress analysis creased with increasing deposition temperature and with time at from several composites, including Al, O3 /Al,O,(c-coating on temperature after deposition. Possible reasons for the strength fibers). The Al, O, /AL,O, composite showed notch insensitivity decrease are discussed milar to other composites. [*44] Boakye EE, Petry MD, Hay RS, Douglas LM. Monazite coatings [53 Cinibulk MK. Hexaluminates as a cleavable fiber-matrix inter on Nextel 720, 610, and Tyranno-SA fiber tows: effects of phase: synthesis, texture development, and phase compatibility, J recursors on fiber strength. Ceram Eng Sci Proc 2000: 21: 229- Eur Cer Soc 2000: 20: 569-82, Review of current state of research Further studies previous two references, with three on hexaluminate as a potential cleavable oxide fiber-matrix ifferent precursors and curing in-line at temperatures betweer 900 and 1300C. Fibers with coatings formed from colloidal 54] Cinibulk MK. Effect of divalent cations on the synthesis of rhabdophane particles showed higher strengths than ed citrate-gel-derived lanthanum hexaluminate powders and films. J fibers after 100 h at 1200C. Discussion of potential Mater Res 1999; 14: 3581-93, Achieved improved [0001] texture gaseous species and coating porosity of thin films. However, degree of basal texture achieved at 145 Holmquist M, Lundberg R, Sudre O, Razzell AG, Molliex L, sufficiently low temp to coat polycrystalline fibers is very lot Benoit J, Adlerborn J Alumina/alumina composite with a porous [55] Callender RL, Barron AR. Facile synthesis of aluminum irconia interphase ocessing,properties and componen taining mixed metal oxides doped carboxylate-alumoxane testing. J Eur Ceram Soc 2000: 20: 599-606, Composite consisting nanoparticles. J Am Ceram Soc 2000: 83: 1777-89 of sapphire fibers with porous zirconia coating in an alumina 56 Callender RL, Barron AR. A new route to hexaluminate ceramics matrix. Moderate strength(100-130 MPa), but retained compo- via a novel transmetalation reaction. Ceram Eng Sci Proc site properties at high temperatures and after aging(1000 h at 1999;20:27-34 1400C). Combustor tiles were manufactured and successfully [57] Saruhan B, Schneider H, Komarneni S, Abothu IR. Electro- tested in a rig at temperatures>1260.C and up to 46 cycles statically deposited surface seeding and promotion of allia. [46] Holmquist M, Adlerborn J, Razzell T, Sudre O, Molliex L tion of sol-gel derived La All1018 coating on oxide J EL Processing and properties of oxide matrix/oxide fibre composite Ceram Soc1999;192427-35 Br Ceram Trans 2000- 99: 266-9 [58] Hay RS, Hermes EE. Sol-gel coatings on continuous ceramic [47] Cinibulk MK, Parthasarathy TA, Keller KA, Mah T-l. Porous fibers. Ceram Eng Sci Proc 1990, 11: 1526-38 are-earth aluminate fiber coatings for oxide-oxide composites. 59] Kerans RJ, Hay RS. Parthasarathy TA. Structural ceramic cor Ceram Eng Sci Proc 2000: 21: 219-28, Strengths of tows and posites. Current Opinion in Solid State Materials Science inicomposites with porous coatings of La-hexaluminate and 99;4:45-51
D.B. Marshall, J.B. Davis / Current Opinion in Solid State and Materials Science 5 (2001) 283–289 289 of High-Temperature Materials, New York: Oxford University YAG with fugitive carbon phase and with black glass matrix. Press, 1999: 229–243. La-hexaluminate coatings degrade tow strengths (40%) but help [40] Davis JB, Marshall DB, Oka KS, Housley RH, Morgan PED. protect the fibers from reaction with the matrix. YAG coatings did Ceramic composites for thermal protection systems. Composites: not degrade the tow strengths. Part A 1999;30:483–8. [48] Boakye E, Hay RS, Petry MD, Parthasarathy TA. Sol–gel [**41] Davis JB, Marshall DB, Morgan PED, Oka KS, Barney AO, synthesis of zircon-carbon precursors and coatings of Nextel Hogenson PA. Damage tolerant thermal protection systems, in: 720TM fiber tows. Ceram Eng Sci Proc 1999;20:165–72, A Proc Space 2000, American Institute of Aeronautics and As- zircon–carbon precursor was continuously coated on Nextel tronautics, Long Beach, CA, 2000. Infiltration and heat treatment 720TM fibers using a sol–gel method. Zircon formation was of fiber tows and fabrics with monazite slurries and solution retarded by the presence of carbon. precursors. Strength degradation observed for solution precursors. [*49] Keller KA, Mah TI, Parthasarathy TA et al. Fugitive interfacial Highest strengths were achieved by infiltration with aqueous carbon coatings for oxide/oxide composites. J Am Ceram Soc slurries of monazite powder, giving composites with a porous 2000;83:329–36, Comparison of effect of interface gap in commonazite matrix. Retained strengths higher than uncoated control posites with dense and porous matrices. specimen [50] Peters PWM, Daniels B, Clemens F et al. Mechanical characteri- [**42] Boakye E, Hay RS, Petry MD. Continuous coating of oxide fiber sation of mullite-based ceramic matrix composites at test temperatows using liquid precursors: monazite coatings on Nextel 720. J tures up to 12008C. J Eur Ceram Soc 2000;20:531–5, Nextel 610 Am Ceram Soc 1999;82:2321–31, Seven different aqueous or fibre-reinforced mullite-based matrix with a 0.1-mm thick carbon ethanolic precursors were used to coat monazite on Nextel 720 coating on fibers. Tensile strength decreased rapidly at tempera- fiber tows using the immiscible liquid displacement method to tures above 8008C. minimize bridging of coating between filaments. Coatings were [51] Halverson HG, Curtin WA. Stress-rupture of Nextel 610/alumina cured in-line at 1200–14008C. Tensile strengths measured from yttria composites. Ceram Eng Sci Proc 2000;21:559–66, HT individual coated fibers showed significant degradation. strength, stress-rupture, and creep of composite with porous [*43] Hay RS, Boakye E, Petry MD. Effect of coating deposition matrix/interface: large decreases in rupture stress at 10508C. temperature on monazite coated fiber. J Eur Ceram Soc [52] Mackin TJ, Roberts MC. Evaluation of damage evolution in 2000;20:589–97, Further studies as in previous reference and ceramic-matrix composites using thermoelastic stress analysis. J microstructural analysis. Tensile strengths of coated fibers de- Am Ceram Soc 2000;83:337–43, Thermoelastic stress analysis creased with increasing deposition temperature and with time at from several composites, including Al O /Al O (c-coating on 23 23 temperature after deposition. Possible reasons for the strength fibers). The Al O /Al O composite showed notch insensitivity 23 23 decrease are discussed. similar to other composites. [**44] Boakye EE, Petry MD, Hay RS, Douglas LM. Monazite coatings [*53] Cinibulk MK. Hexaluminates as a cleavable fiber-matrix interon Nextel 720, 610, and Tyranno-SA fibert tows: effects of phase: synthesis, texture development, and phase compatibility. J precursors on fiber strength. Ceram Eng Sci Proc 2000;21:229– Eur Cer Soc 2000;20:569–82, Review of current state of research 36, Further studies as in previous two references, with three on hexaluminates as a potential cleavable oxide fiber-matrix different precursors and curing in-line at temperatures between interphase. 900 and 13008C. Fibers with coatings formed from colloidal [54] Cinibulk MK. Effect of divalent cations on the synthesis of rhabdophane particles showed higher strengths than uncoated citrate-gel-derived lanthanum hexaluminate powders and films. J fibers after 100 h at 12008C. Discussion of potential effects of Mater Res 1999;14:3581–93, Achieved improved [0001] texture gaseous species and coating porosity. of thin films. However, degree of basal texture achieved at [*45] Holmquist M, Lundberg R, Sudre O, Razzell AG, Molliex L, sufficiently low temp to coat polycrystalline fibers is very low. Benoit J, Adlerborn J. Alumina/alumina composite with a porous [55] Callender RL, Barron AR. Facile synthesis of aluminum conzirconia interphase — processing, properties and component taining mixed metal oxides using doped carboxylate-alumoxane testing. J Eur Ceram Soc 2000;20:599–606, Composite consisting nanoparticles. J Am Ceram Soc 2000;83:1777–89. of sapphire fibers with porous zirconia coating in an alumina [56] Callender RL, Barron AR. A new route to hexaluminate ceramics matrix. Moderate strength (100–130 MPa), but retained compo- via a novel transmetalation reaction. Ceram Eng Sci Proc site properties at high temperatures and after aging (1000 h at 1999;20:27–34. 14008C). Combustor tiles were manufactured and successfully [57] Saruhan B, Schneider H, Komarneni S, Abothu IR. Electrotested in a rig at temperatures.12608C and up to 46 cycles. statically deposited surface seeding and promotion of crystalliza- [46] Holmquist M, Adlerborn J, Razzell T, Sudre O, Molliex L. tion of sol–gel derived La Al11018 coating on oxide fibers. J Eur Processing and properties of oxide matrix/oxide fibre composite. Ceram Soc 1999;19:2427–35. Br Ceram Trans 2000;99:266–9. [58] Hay RS, Hermes EE. Sol–gel coatings on continuous ceramic [47] Cinibulk MK, Parthasarathy TA, Keller KA, Mah T-I. Porous fibers. Ceram Eng Sci Proc 1990;11:1526–38. rare-earth aluminate fiber coatings for oxide-oxide composites. [59] Kerans RJ, Hay RS. Parthasarathy TA. Structural ceramic comCeram Eng Sci Proc 2000;21:219–28, Strengths of tows and posites. Current Opinion in Solid State & Materials Science minicomposites with porous coatings of La-hexaluminate and 1999;4:445–51