Continuous Fiber Ceramic Composites Research Articles

Advancements in carbon fibre reinforced ultra-refractory ceramic composites: Effect of rare earth oxides addition

Continuous carbon fibre ceramic matrix composites capable of tolerating multiple thermal-shock cycles and resisting ablation are needed for aerospace and hypersonic systems. Carbon fibre around 50 vol% and ultra-refractory matrices are fundamental parameters. The influence of rare earth (RE) oxides on the microstructure and mechanical properties of carbon fibre-ZrB2/SiC composites was investigated. Materials were produced by slurry infiltration and hot pressing. The addition of Y2O3, La2O3 and CeO2 led to the formation of lamellar boro-carbides that improved the densification, while Sc2O3 promoted the formation of (Zr,Sc)B2 solid solutions in the matrix. All these composites exhibited improved mechanical properties compared to a RE-free baseline, with room temperature strengths and toughness above 330 MPa and 9 MPa m0.5, respectively, and strengths above 600 MPa at 1500 °C. The lamellar phase was identified as a fibre by-product with general formula REB2C2. Only CeO2 was detrimental on the long run due to its high reactivity with humidity which induced swelling and jeopardized the structural stability of the composite.This study revealed new fundamental insights into the microstructure evolution of carbon-fibre refractory composites and its impact on the mechanical properties, which will contribute to the development of new generation of reusable ceramic matrix composites for harsh environments.

FEM predictions of damage in continous fiber ceramic matrix composites under transverse tension using the crack band method

This paper develops a numerical micromechanics fracture model based on the crack band methodology for the prediction of damage in continuous fiber ceramic matrix composites (CMCs). The energy based crack band formulation offers mesh objective predictions in finite element simulations. Detailed finite element models of CMCs are created based on the actual microstructure and compared with randomly created representative volume elements (RVE). The influence of geometrical inhomogeneities, such as fiber clustering and variations of the fiber coating thickness, on the stress-strain response and the crack development are investigated. Furthermore, FEM models of multi-layer cross-ply laminates are created including thousands of explicitly modeled fibers and fiber coatings. Crack density predictions are compared with well established analytical models by Laws and Dvorak [1] and Nairn [2]. An eight layer FEM model is used to predict damage propagation within each layer. The Numerical prediction of the stress-strain response is compared with experimental results of smooth bar tensile coupons.

Multiscale damage characterization in continuous fiber ceramic matrix composites using digital image correlation

Damage in continuous fiber CMCs with weakly bonded fiber–matrix interfaces evolves in several stages that span multiple length scales. Comprehensive damage characterization necessitates identifying how damage initiates as well as how it accumulates (through final failure), which is not feasible with information gathered from a single length scale. Using digital image correlation to measure full-field surface deformations, damage evolutions in continuous fiber SiC/SiC laminates were analyzed at three distinct length scales: constituent, lamina, and laminate. Constituent scale analyses indicated that fine matrix cracks initiated in localized regions of transverse fiber coatings at low stresses. Investigations at the larger lamina scale revealed that some, but not all, of the coating cracks evolved into matrix cracks, the propagation of which was dependent on the state of stress near the crack tip and the local microstructure. Many of these matrix cracks morphed into cracks large enough to be detected at the (largest) laminate scale. The density of the large matrix cracks increased with load, reaching saturation prior to failure. While the constituent scale identifies when (with respect to stress state) and where (with respect to local microstructure) damage initiates, the lamina scale elucidates damage progression between neighboring constituents. Only laminate scale fields of view are large enough to capture the accumulation of the large matrix cracks that ultimately lead to final fracture. However, as spatial resolution is reduced at this scale, finer cracks (which may provide pathways for environmental ingress) go undetected. As each length scale provides a unique perspective of damage evolution in CMCs, multiscale analysis is essential for comprehensive damage characterization.

Cyclic creep and recovery behavior of Nextel™720/alumina ceramic composite at 1200 °C

The cyclic creep and recovery behavior of an oxide–oxide continuous fiber ceramic composite was investigated at 1200°C in laboratory air and in steam environments. The composite consists of a porous alumina matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. The main objective of this study was to assess the influence of various sustained creep and cyclic creep loading histories on the creep lifetime, creep strain rate, accumulated creep strain as well as on the recovery of creep strain at near zero stress. Cyclic creep-recovery tests were performed for maximum stress levels of 100 and 125MPa with creep and recovery periods ranging from 3min to 1h. In laboratory air, lifetimes produced in cyclic creep and recovery tests significantly exceeded those obtained in sustained creep tests. Introduction of intermittent periods of unloading and recovery at near zero stress into the creep loading history resulted in an appreciable improvement in creep lifetime. Presence of steam considerably degraded the material performance. In steam, lifetimes produced in cyclic creep and recovery tests were close to those obtained in sustained creep tests. Composite microstructure, as well as damage and failure mechanisms were investigated.

Effects of steam environment on creep behavior of Nextel™720/alumina–mullite ceramic composite at elevated temperature

The tensile creep behavior of an oxide–oxide continuous fiber ceramic composite was investigated at 1000 and 1100 °C in laboratory air and in steam. The composite consists of a porous alumina–mullite matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. The tensile stress–strain behavior was investigated and the tensile properties measured. Tensile creep behavior was examined for creep stresses in the 70–140 MPa range. The presence of steam accelerated creep rates and dramatically reduced creep lifetimes. The degrading effects of steam become more pronounced with increasing temperature. At 1000 °C, creep run-out (set to 100 h) was achieved in all tests. At 1100 °C, creep run-out was achieved in all tests in air and only in the 87.5 MPa test in steam. Composite microstructure, as well as damage and failure mechanisms were investigated.

Experimental Investigation of Optimal Nanoparticle Inclusion for Enhanced Flexural Performance in Continuous Fiber Ceramic Nanocomposites

This work reports the effects of using varying weight percentage of nanoparticle inclusions on mechanical performance of continuous fiber ceramic composites. The ceramic fiber reinforcement was NicalonTM, and KiON CERASET ® preceramic polymer was mixed with nanoparticle inclusions in the presence of a surfactant agent, which gave good dispersion of the particles within the matrix. Yttrium oxide nanoparticles with an average size of 29 nm was used as the inclusion with varying weight percentages of 5, 10, 15, and 20%. For comparison, samples without nanoparticles were also manufactured. Two different types of nanoparticle filled composites were manufactured. The first one followed neat preceramic polymer reinfiltration cycle, whereas the second system was manufactured with corresponding nanoparticle dispersed preceramic polymer reinfiltration. A characterization analysis of the samples using scanning electron microscopy revealed proper dispersion of nanoparticle along with good quality of the parts. In general, the weight gain percentage at each stage of reinfiltration/pyrolysis for both types of nanoparticle filled ceramic composites is consistently less than that for ceramic composites manufactured without nanoparticle. This indicates the compactness of the material and retention of shape during the B-staging. Four-point bending test was also conducted to evaluate the mechanical performance of the ceramic composite samples at room temperature. Nanoparticle filled samples consistently showed significant improvement in flexural strength compared to their counterparts without nanoparticle reinforcement.

Creep of Nextel™720/alumina–mullite ceramic composite at 1200 °C in air, argon, and steam

The tensile creep behavior of an oxide–oxide continuous fiber ceramic composite was investigated at 1200 °C in laboratory air, in steam and in argon. The composite consists of a porous alumina–mullite matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. The tensile stress–strain behavior was investigated and the tensile properties measured at 1200 °C. The elastic modulus was 74.5 GPa and the ultimate tensile strength was 153 MPa. Tensile creep behavior was examined for creep stresses in the 70–140 MPa range. Primary and secondary creep regimes were observed in all tests. Creep run-out (set to 100 h) was achieved in laboratory air for creep stress levels ⩽91 MPa. The presence of either steam or argon accelerated creep rates and reduced creep lifetimes. Composite microstructure, as well as damage and failure mechanisms were investigated.

Control of Interface Properties in Oxide Composites Via Fugitive Coatings

Long‐term durability of ceramic composites requires the retention of weak interfaces to promote crack deflection and subsequent sliding at the fiber–matrix boundary. The present article addresses the efficacy of fugitive carbon coatings in achieving this goal in all‐oxide systems. A solution precursor route with a low‐temperature pyrolysis treatment has been devised and implemented for coating oxide fibers within a woven cloth. The coating is oxidized following completion of matrix processing to produce an interfacial gap. Upon comparing the mechanical properties of two continuous fiber ceramic composites—with and without a fugitive coating—the gap is shown to reduce the interfacial sliding resistance and significantly enhance the fracture resistance of the composite. It also enables an extension in the useful life of the composite when subjected to long‐term (1000 h) exposure at high temperature (1200°C). The results also suggest that modifications in the coating thickness may provide additional enhancement in composite durability.

Effects of steam environment on creep behavior of Nextel™720/alumina ceramic composite at elevated temperature

The tensile creep behavior of an oxide–oxide continuous fiber ceramic composite (CFCC) was investigated at 1000 and 1100 °C in laboratory air and in steam. The composite consists of a porous alumina matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. The tensile stress–strain behavior was investigated and the tensile properties measured. The influence of the loading rate on tensile stress–strain response and on tensile properties at 1100 and 1200 °C in steam was also explored. A change in loading rate by four orders or magnitude had a profound effect on tensile strength. Tensile creep behavior was examined for creep stresses in the 80–150 MPa range. Primary and secondary creep regimes were observed in creep tests at all temperatures investigated. Creep rates increased with increasing temperature and creep stress. The presence of steam accelerated creep rates and dramatically reduced creep life. The detrimental effects of steam become progressively more pronounced with increasing temperature. At 1000 °C, creep run-out defined as 100 h at creep stress was achieved in all tests. At 1100 °C, creep run-out was achieved in all tests in air and only in the 100 MPa test in steam. The residual strength and modulus of all specimens that achieved run-out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated.

Creep behavior of Nextel™720/alumina ceramic composite with ±45° fiber orientation at 1200 °C

The tensile creep behavior of an oxide–oxide continuous fiber ceramic composite (CFCC) with ±45° fiber orientation was investigated at 1200 °C in laboratory air, in steam and in argon. The composite consists of a porous alumina matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous-matrix for flaw tolerance. The tensile stress–strain behavior was investigated and the tensile properties measured at 1200 °C. The elastic modulus was 46 GPa and the ultimate tensile strength (UTS) was 55 MPa. Tensile creep behavior was examined for creep stresses in the 15–45 MPa range. Primary and secondary creep regimes were observed in all tests. Creep run-out (set to 100 h) was achieved in all test environments for creep stress levels ⩽35 MPa. At creep stresses >35 MPa, creep performance was best in laboratory air and worst in argon. The presence of either steam or argon accelerated creep rates and reduced creep life. Composite microstructure, as well as damage and failure mechanisms were investigated.

Effects of frequency and environment on fatigue behavior of an oxide–oxide ceramic composite at 1200 °C

The effect of frequency on fatigue behavior of an oxide–oxide continuous fiber ceramic composite (CFCC) was investigated at 1200 °C in laboratory air and in steam environment. The composite consists of a porous alumina matrix reinforced with laminated, woven mullite–alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. Tension–tension fatigue tests were performed at frequencies of 0.1 and 10 Hz for fatigue stresses ranging from 75 to 170 MPa. Fatigue run-out was defined as 10 5 cycles at the frequency of 0.1 Hz and as 10 6 cycles at the frequency of 10 Hz. The CFCC exhibited excellent fatigue resistance in laboratory air. The fatigue limit was 170 MPa (88% UTS at 1200 °C). The material retained 100% of its tensile strength. Presence of steam significantly degraded the fatigue performance, with the degradation being most pronounced at 0.1 Hz. Composite microstructure, as well as damage and failure mechanisms were investigated. Examination of fracture surfaces revealed higher degrees of fiber pull-out in specimens tested at 10 Hz, indicating weakening of the fiber/matrix interface. A qualitative spectral analysis showed evidence of silicon species migration from the fiber to the matrix.

Effects of steam environment on high-temperature mechanical behavior of NextelTM720/alumina (N720/A) continuous fiber ceramic composite

Abstract Mechanical behavior of an oxide–oxide continuous fiber ceramic composite (CFCC) consisting of a porous alumina matrix reinforced with laminated, woven mullite/alumina fibers (Nextel TM 720) was investigated at 1200 and 1330 °C in laboratory air and in 100% steam environments. CFCC has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. Tension–tension fatigue behavior was studied for fatigue stresses ranging from 100 to 170 MPa at 1200 °C, and for fatigue stresses of 50 and 100 MPa at 1330 °C. Tensile creep behavior was examined for creep stresses ranging from 80 to 154 MPa at 1200 °C, and for creep stresses of 50 and 100 MPa at 1330 °C. At 1200 °C, the CFCC exhibited excellent fatigue resistance in laboratory air. The fatigue limit (based on a run-out condition of 10 5 cycles) was 170 MPa (88% UTS at 1200 °C). The material retained 100% of its tensile strength. Presence of steam caused noticeable degradation in fatigue performance at 1200 °C. Fatigue resistance at 1330 °C was poor. In creep tests, primary and secondary creep regimes were observed. Minimum creep rate was reached in all tests. At 1200 °C, creep rates were 10 −8 –10 −5 s −1 and maximum time to rupture was 255 h. At 1330 °C, creep rates were 10 −7 –10 −5 s −1 and maximum time to rupture was 87 h. Presence of steam accelerated creep rates and dramatically reduced creep life.

Anisotropic damage of alumina/alumina CFCCs under long term high temperature exposure: Investigations by ultrasonic stiffness measurements and quasi-static tests

The present work deals with the development of anisotropic damage in alumina/alumina continuous fiber ceramic composites (CFCCs). The composites were isothermally exposed to a corrosive/high temperature environment at 1100°C, which simulates the working conditions of a gas turbine. Stiffness matrix components and strength were experimentally defined as a function of exposure duration by means of ultrasonic stiffness measurements and quasi-static tensile tests. In order to determine the stiffness matrix components, a new ultrasonic stiffness characterisation technique was employed. According to this method, the through transmission phase velocities are measured using a custom built immersion set-up. The experimental data are subsequently used in order to solve the inverse scattering problem and reconstruct the stiffness matrix of the composite at successive thermal exposure levels. The stiffness matrix of the composite was assumed to be orthotropic. Damage functions were formulated to describe the high temperature/corrosive exposure effect on the stiffness matrix of the composite. Finally, quasi-static tensile tests were used to assess the stiffness reduction of the composite and compare the values to those acquired non-destructively. The effect of exposure time on the strength of the composite was determined in the same way.

Polymeric precursor pyrolysis for flexural property evaluation of continuous fiber ceramic nanocomposites with nanoparticles

The effects of nanoparticles on processing and flexural mechanical performance of Nicalon/KiON CERASET ® continuous fiber ceramic composites by preceramic polymer pyrolysis method have been investigated. Five different nanoparticles varying in size from 15 to 55 nm were used. These nanoparticles are: titanium oxide, yttrium oxide, zinc oxide, silicon carbide, and carbon. Ceramic fiber reinforcements (Nicalon™) and preceramic polymer (KiON CERASET ®) was mixed with nano-size fillers in the presence of a surfactant agent to give a good dispersion of the particles during the process. Two different types of nanoparticle filled composites were manufactured. The first one followed neat preceramic polymer reinfiltration cycle; whereas the second system was manufactured with corresponding nanoparticle dispersed preceramic polymer reinfiltration. For comparison purposes, samples without nanoparticles were also manufactured. A characterization analysis of the samples using scanning electron microscopy revealed good quality of the parts. In general, the weight gain percentage at each stage of reinfiltration/pyrolysis for both types of nanoparticle filled ceramic composites is consistently less than that for ceramic composites manufactured without nanoparticles. This indicates the compactness of the nanocomposites. Four-point bending test was also conducted to evaluate the flexural mechanical performance of the ceramic composites samples at room temperature. Nanoparticle filled samples consistently showed significant improvement in flexural strength compared to their counterparts without nanoparticle reinforcement.

Application of Thermal Barrier Coatings on Combustion Chamber Liners – A Review.

Thermal barrier coatings (TBC) help to reduce the temperature of combustion chamber liner by 473-573K during operation on being aided by swirls of film cooling air. Versatility and low production cost make air plasma spray (APS) TBCs more attractive on liners. However spinal formation at the top to bond coat interface induces ceramic sintering rate and forms thermally grown oxide (TGO) growth. Lifing of engines is attempted to utilize existing design and remnant life within design constrains by giving emphasis on coating philosophies. A proper and efficient substitute with multimetallic bond coat and ceramic topcoat yields longer hours of exposure. Parallel removal of harmful elements in the liner material, restriction on the use of poor quality fuels, and atmospheric effects increase life. Studies of remnant life assessment have been found to be based on control of parameters that check TGO growth, increase adhesion of thicker TGO and restrict ceramic top coat sintering. For example, ceria or lanthana stabilized zirconia transform at comparatively higher temperature than yttria stabilized zirconia. The current scenarios of protection have been changed to replacements by continuous fiber ceramic composite (CFCC), and ceramic matrix composites (CMC) component; e.g. Sylramic, Nicalon, Naxtal, and Ceracurb. Non-destructive examination of ceramic translucence based on Parker's optical property produces in-situ information about ceramic degradations.

Mechanical behavior and numerical estimation of fracture resistance of a SCS6 fiber reinforced reaction bonded S13N4 continuous fiber ceramic composite

Continuous fiber ceramic composites (CFCCs) have advantages over monolithic ceramics: Silicon Nitride composites are not well used for application because of their low fracture toughness and fracture strength, but CFCCs exhibit increased toughness for damage tolerance, and relatively high stiffness in spite of low specific weight. Thus it is important to characterize the fracture resistance and properties of new CFCCs materials. Tensile and flexural tests were carried out for mechanical properties and the fracture resistance behavior of a SCS6 fiber reinforced Si3N4 matrix CFCC was evaluated. The results indicated that CFCC composite exhibit a rising R curve behavior in flexural test. The fracture toughness was about 4.8 MPa m1/2 , which resulted in a higher value of the fracture toughness because of fiber bridging. Mechanical properties as like the elastic modulus, proportional limit and the ultimate strength in a flexural test are greater than those in a tensile test. Also a numerical modeling of failure process was accomplished for a flexural test. This numerical results provided a good simulation of the cumulative fracture process of the fiber and matrix in CFCCs.

A New Design Methodology for High Temperature Structural Components Made of Continuous Fibre Ceramic Composites Exhibiting Thermally Induced Anisotropic Damage

Continuous Fibre Ceramic (Matrix) Composites (CFCCs) have found during the last decade numerous of industrial applications in a variety of technological areas, where structural components are subjected to high temperature combined with significant mechanical loading. The present work deals with the application of an innovative design methodology for the development of an industrial gas turbine combustor chamber made of oxide/oxide composite materials. Oxide/oxide composites offer high-temperature structural stability without the need of any kind of oxidation protection and thus permit the increase of working temperature of the gas turbine, increasing the efficiency of the system and decreasing NOx emissions. Since, oxide/oxide composites degrade their structural properties as a function of the operating temperature (for temperature higher than 1000°C) and the exposure time, an incremental approach has been introduced as a structural design methodology for the combustion chamber, where each increment represents a thermal exposure stage. The data set required for the application of the present design approach, was obtained through an extensive material characterization program based on the measurement of the anisotropic properties of oxide/oxide composites using ultrasonic techniques.

Processing and Performance of Continuous Fiber Ceramic Composites by Preceramic Polymer Pyrolysis: II - Resin Transfer Molding

Processing and Performance of Continuous Fiber Ceramic Composites by Preceramic Polymer Pyrolysis: II - Resin Transfer Molding

Processing and Performance of Continuous Fiber Ceramic Composites by Preceramic Polymer Pyrolysis: I - Filament Winding

Processing and Performance of Continuous Fiber Ceramic Composites by Preceramic Polymer Pyrolysis: I - Filament Winding

Processing and Performance of Continuous Fiber Ceramic Composites by Preceramic Polymer Pyrolysis: II—Resin Transfer Molding

Vacuum Assisted Resin Transfer Molding (VARTM) was used in conjunction with preceramic polymer pyrolysis to manufacture Continuous Fiber Ceramic Composites (CFCCs). Two VARTM techniques were used: (a) the use of injection pressure in the presence of a vacuum and (b) the use of vacuum only without the injection pressure. After initial testing, eight CFCC tubes were fabricated using these techniques. The matrix material used was Blackglas™. C-Nicalon™ in the form of woven fabric and BN-Nextel ®312 in the form of braided textile were used as reinforcements. C-Nicalon™ CFCC tubes with 4%–6% porosity, 55%–57% fiber volume fraction, and 2.12–2.18 g/cm3 density reached convergence by weight in 10 cycles (with about 17 hours per cycle), while BN-Nexlet ®312 CFCC tubes with 4%–6% porosity, 70%–72% fiber volume fraction, and 2.42–2.48 g/cm3 density converged by weight in 8 cycles. TheVARTMprocessing time averaged 15 minutes for each tube. The mechanical performance of the components was evaluated at room and high temperatures using a C-ring test. Scanning Electron Microscopy (SEM) was employed to study the microstructure of the parts. The results show that the without injection pressure technique offers a promising method to produce tubular CFCCs in terms of lower manufacturing costs, part uniformity, and enhanced mechanical properties. BN-coating performs better at high temperature compared with C-coating. Also, a combination of BN-coating and a textile braided architecture of fiber preform proved to enhance the performance of the manufactured CFCCs. Finally, the mechanical performances of the manufactured CFCC tubes using VARTMtechnique were compared with those using a cure-on-the-fly filament winding technique for a similar geometry using the same materials.