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Ox/ox CMC based on Nextel 610™ fibers with 75 wt% alumina – 25 wt% zirconia matrix have been joined by a glass-ceramic and tested in creep in four-point bending (DIN EN 820–4) up to 50 h at 850 °C and 1000 °C, between 32 and 41 MPa. As a comparison, the creep limit of the non-joined ox/ox CMC was investigated in this range and also at higher temperatures and stresses. The creep experiments at 850 °C did not show any significant difference between joined and ox/ox CMC after 50 h, while a certain one was detected at 1000 °C on joined ox/ox CMC, suggesting that its creep mechanism is dominated by visco-elastic flow of the glass-ceramic.

This study analyzed the influence of the sample volume, number of tested specimen, and testing method on the flexural strength of fabric-reinforced ceramic matrix composites. For this purpose, seven different batches of C/C-SiC were prepared with four different sample thicknesses to determine the flexural strengths and Weibull moduli by three- and four-point flexural tests. The result showed that C/C-SiC exhibits a size effect of strength under bending load because a decrease of measured flexural strength with increased specimen size was observed. This size effect was discussed regarding the Weibull weakest link approach and the concept of quasi-brittle materials.The determined Weibull moduli were comparable for the same load condition but dissimilar for the identical material if the load condition were changed from three- to four-point bending. Hence, the Weibull modulus was found to be not an inherent material constant for C/C-SiC and the Weibull weakest link approach seems not appropriate.

Ceramic Matrix Composites (CMCs) are increasingly demanded especially for the production of structural components for several industries such as aerospace because of their excellent thermo-mechanical and fatigue properties. As one of the last production steps final machining is necessary to meet the required tolerances. From the economic point of view final machining of CMCs is highly critical and special knowledge is assumed to avoid irreparable damage, because of their heterogeneous, anisotropic and brittle nature. In this work diamond grinding and diamond milling have been applied to a 2D C/C-SiC composite at various feed rates and cutting speeds and in both main laminate directions, in-plane and out-of-plane. The microstructures of in-plane and out-of-plane machining indicate different material removal mechanisms due to different composite architecture. Increasing feed rate leads generally to more surface defects and consequently to higher roughness. Little influence on the four-point-bending strength was observed when changing the machining speed.

The synthesis of C/C-SiC via liquid silicon infiltration (LSI) with thermoplastic carbon precursors can lead to the formation of macropores in the C/C state. The macro-pore pattern formation can be controlled and used as a new level in microstructure for ceramic matrix composites. The pore formation occurs in the CFRP state with the remelting of the thermoplastic matrix and can be fixed to the C/C state after liquid phase pyrolysis. The macro-pores are primarily induced by a non-linear elastic recovery of the fiber preform and not via gas formation and release during pyrolysis. The formation of the macroporosity is described and explained. These pores can be tailored by process control in size and shape. The pore shapes can vary from isolated spherical pores to an interconnected tube like macro-pore network. The relationship between starting setting variables of the fiber preform, the process conditions, and the resulting structure are discussed.

A novel pre-impregnated fiber-preform (prepreg) manufacturing process for Nextel™610/ Al2O3-ZrO2 oxide fiber composites (OFC) was developed, using glycerol containing slurries.. It provides a simple and cost-effective way of producing OFC and lead to mean flexural strengths of up to 392 MPa. The use of glycerol in the slurry lead to reproducible and storable prepregs. The correlations between slurries with different glycerol contents and varying values of relative humidity during conditioning were investigated. By subjecting prepregs containing 16 wt% or 26 wt% slurries to different drying conditions, their suitability for accelerated drying methods was investigated. The storability of prepregs was studied under various storing conditions for at least four weeks. Sorption and desorption behavior of these slurries were investigated by Dynamic Vapor Sorption (DVS).. A glycerol content of 26 wt% proved to be favorable, because it provides a reproducible and robust process and enables ready-for-use prepregs only 15 min after infiltration.

Ceramic matrix composite (CMC) friction materials show promising tribological properties. Typically, carbon ceramic brake discs consist of a C/SiC rotor which is joined to a brake disc bell. Within this work, a novel metal-ceramic hybrid brake disc, consisting of C/SiC friction segments which are mounted by screws onto an aluminium carrier body, was designed and investigated. A prototype was built which was tribologically tested with three different brake pad materials, LowMet reference, modified SF C/SiC as well as C/C. A constant starting sliding velocity of 20 m/s and braking pressures of 1, 2 and 3 MPa were investigated. To simulate emergency braking conditions ten consecutive brake applications were carried out in close succession for each brake pad material and braking pressure. The C/C brake pad material showed the highest average coefficient of friction followed by the LowMet and C/SiC material. However, the wear rates of the C/C and LowMet material were orders of magnitude higher compared to the C/SiC material.

The appropriate assessment of mechanical properties is essential to design ceramic matrix composites. The size effect of strength plays a key role for the material understanding and the transfer from lab-scale samples to components. In order to investigate the size effect for carbon fiber-reinforced silicon carbon (C/C-SiC) under tensile load, a tensile testing with a minimum of deviation from the pure tensile loading is necessary. Hence, a hybrid edge/face-loading test device for self-alignment and centering of C/C-SiC tensile samples was developed, evaluated and proved to ensure pure tensile load. The mechanical analysis of more than 190 samples with two different cross-sections fabricated from the same material population revealed no significant difference in tensile strength. Although the volume under load was increased from 129 to 154 mm3, the tensile strengths of 162 ± 7 and 164 ± 6 MPa did not change. These results are discussed regarding the weakest link and energetic size effect approaches.

With an overall collection and recycling rate of 74%, the material cycle for glass packaging is well established in the European Union. However, knowledge of the composition of the recycled glass cullet is necessary to avoid creeping accumulation of undesirable contaminants into the material cycle. Due to their toxic properties, this applies in particular for heavy metals, for example, lead. The state‐of‐the‐art technology for detection of lead in recycling glass sorting is X‐ray fluorescence (XRF). Due to lower regulatory demands, as well as increasingly economical hardware, laser‐based detection techniques, like Laser‐Induced Breakdown Spectroscopy (LIBS) may provide an alternate approach in industrial glass sorting to reach comparable detection limits and rates. In our work, CO2‐LIBS was investigated as an alternative tool for the determination of lead in glass cullet. Instead of usually utilized spectrometers, a combination of spectral filters and photodiode was employed to facilitate a fast detection rate. Glass samples with different lead content were investigated in two spectral ranges with respect to detection limits, detection speed, and accuracy. The results are compared to a commercial XRF‐sorting machine for glass cullet. It was found that comparable speeds and accuracies for lead detection in glasses can be reached.

Damage analyses of a ceramic matrix composite during fatigue and quasi-static loads were performed by acoustic emission (A.E.) monitoring. The material studied was a 2.5D C/C-SiC composite produced by chemical vapor infiltration followed by liquid silicon infiltration. The analysis done during the first 200 cycles of a fatigue test showed that the number of A.E. hits is a good parameter for the quantification of damage. Furthermore, the A.E. hit energy was associated with the type of damage. In this sense, the damage developed during the fatigue loading was related to matrix crack initiation, propagation and re-opening, as well as fiber-matrix friction. Quasi-static tests on post-fatigue samples showed that the previous fatigue loadings increased the material`s damage threshold and hindered the development of new damage. Particular attention was given to the sample after 2,000,000 cycles as this sample showed distinct A.E. signals that could be related to fiber debonding.

A novel, vacuum-assisted single-step slurry infiltration process (SIP) for the manufacturing of OFCs (Oxide Fiber Composites) was developed. It provides a simple and cost-effective way to infiltrate near-net shape fiber preforms, such as radial braided fiber architectures. NextelTM 610 fabrics were infiltrated with an alumina-zirconia slurry in order to obtain NextelTM 610/Al2O3-ZrO2 composites, which were investigated by SEM and three-point-bending tests. Vacuum pressures varying from 50 mbar to 700 mbar were tested for the SIP as well as varying solid contents between 50 wt.% to 71 wt.% and different aids (manual support by Teflon roller, pressure infiltration) during the initial infiltration. As advancement of the SIP, a double-step infiltration process (DIP) was developed, to ensure a more homogeneous infiltration of the fiber bundles. A comparison of microstructure and mechanical properties of the OFCs manufactured by SIP and DIP with OFCs manufactured by a prepreg process was made. To demonstrate the feasibility of the developed DIP process for complex fiber preforms, a burner nozzle was fabricated by infiltrating a radial braided preform.

Carbon fiber fabric reinforced plastics were pyrolyzed at temperatures between 900 °C and 1600 °C to convert them into carbon/carbon (C/C) composites. The effects of pyrolysis temperatures on the microstructure, mechanical properties, and especially on the capillary infiltration behavior of C/C composites, suitable for liquid silicon infiltration (LSI), were investigated. The porosity of these C/C composites shows a decreasing trend with increasing pyrolysis temperature. The established model can explains the pyrolysis mechanism and the infiltration behaviors. Within the initial stage, the capillary infiltration rate of C/C composites with the model fluid water increases rapidly. In the second stage, where thermal imaging indicates that water has reached the top area of the plates at the initial stage. Capillary infiltration rate, based on water infiltration experiments mass increase, decreases because the shrinkage of micro-delamination take place at higher pyrolysis temperature. In combination with LSI results, a model for the capillary infiltration behavior of C/C is proposed.

Steel materials suffer extensive creep by the application at temperatures of about 700 °C and pressures about 350 bar in a power plant environment. The presented concept overwraps a steel pipe with a ceramic matrix composite (CMC) jacket in order to support the steel pipe and provide high temperature strength. Finite Element simulations show the influence of the wall thickness of CMC jacket and the coefficient of thermal expansion (CTE) on circumferential stresses within the hybrid metal ceramic pipe. Suitable fiber and matrix materials were studied, composites fabricated and mechanical properties determined. Finally, a prototype was designed in order to confirm the feasibility of the concept. The lifetime of a pure steel pipe was increased by more than four-fold by the additional CMC jacket.

Alumina (Nextel™ 610) fibre reinforced YAG-ZrO2 matrix composites were successfully joined by using different brazing alloys, metallic interlayers and a glass-ceramic. All joints were mechanically stable and free of cracks. Three commercial brazing alloys and a new alloy based on Ti/Cu/Al interlayers were selected to join these composites for applications in a non-oxidizing environment. A glass-ceramic based on SiO2-Al2O3-CaO-MgO was developed in case the joined component needs to be oxidation resistant. To evaluate the thermal stability, all joined composites were aged up to 100 h in air at 550 °C for brazing joints or 850 °C and 930 °C for glass-ceramic joints. The mechanical strength was measured using single lap and four point bending tests before and after ageing. Four point bending tests on glass-ceramic joined samples showed an average joint strength of about 70 MPa which is 35% of as-received composites.

Fiber composites with a three-dimensional braided reinforcement architecture have higher fiber volume content and Z-fiber content compared to a two-dimensional braided reinforcement architecture, as a result, the shear strength increases. Porous oxide fiber composites (OFCs) have the inherent weakness of a low interlaminar shear strength, which can be specifically increased by the use of a three-dimensional fiber reinforcement. In this work, the braiding process chain for processing highly brittle oxide ceramic fibers is modified, as a consequence, a bobbin, which protects the filament, is developed and quantitatively evaluated on a test rig with regard to tension and filament breakage. Subsequently, a braiding process is designed which takes into account fiber-protecting aspects, and a three-dimensional reinforced demonstrator is produced and tested. After impregnation with an Al2O3-ZrO2 slurry, by either a prepreg process or a vacuum-assisted process, as well as subsequent sintering, the three-dimensional braid-reinforced OFC exhibits an interlaminar shear strength (ILSS) which is higher than that of two-dimensional braid- or fabric-reinforced samples by 64–95%. The influence of the manufacturing process on the relative macropore content is investigated and correlated with the mechanical properties.

High temperature-resistant fabrics can be used as a reinforcement structure in ceramic matrix composites. They often need a coating for oxidation protection and mechanical decoupling from the matrix. Atomic layer deposition (ALD) provides very thin conformal coatings even deep down into complex or porous structures and thus might be a suitable technique for this purpose. Carbon fiber fabrics (size 300 mm × 80 mm) and SiC fiber fabrics (size 400 mm × 80 mm) were coated using ALD with a multilayer system: a first layer made of 320 cycles of alumina (Al2O3) deposition, a second layer made of 142 cycles of titania-furfuryl alcohol hybrid (TiO2-FFA), and a third layer made of 360 cycles of titanium phosphate (TixPOy). Scanning electron microscopy reveals that the coatings are uniform and that the thickness of each layer is almost independent of the place in the reactor while coating. Appearance and thickness do not show any dependence on the type of fiber used as a substrate. Energy dispersive x-ray spectroscopy confirmed the expected elemental composition of each layer. Thermogravimetric analysis under oxidizing environment revealed that the first layer increases the onset temperature of fiber oxidation significantly, while the following two layers improve the oxidative protection only to a much smaller degree. Varying the geometry and size of the sample holder and especially the stacking of several fabric specimens on top of each other allowed increasing the total area of coated fabric up to 560 cm2 per batch. It was demonstrated that four-layered fiber coatings could be obtained with high uniformity even on these much more complicated geometries.

Environmental barrier coatings are required to protect Si3N4 against hot gas corrosion and enable its application in gas turbines, among which yttrium and ytterbium silicate-coatings stand out. Thus, the polymer-derived ceramic route was used to synthesize these silicates for basic investigations regarding their intrinsic properties from a mixture of Y2O3 or Yb2O3 powders and the oligosilazane Durazane 1800. After pyrolysis above 1200 °C in air, the silicates are predominant phases. The corrosion behaviour of the resulting composites was tested at 1400 °C for 80 h in moist environments. The material containing x2-Yb2SiO5 and Yb2Si2O7 undergoes the lowest corrosion rate (−1.8 μg cm−2 h−1). Finally, the processing of Y2O3/Durazane 1800 as well-adherent, crack-free and thick (40 μm) coatings for Si3N4 was achieved after pyrolysis at 1400 °C in air. The coating consisted of an Y2O3/Y2SiO5 top-layer and an Y2O3/Y2Si2O7 interlayer due to the interaction of the coating system with the substrate.

High purity SiC nanostructures were grown in situ on the surfaces of C/SiC composites by the chemical vapor reaction route to improve the anti-oxidation capability of C/SiC composites. It was found that the SiC nanostructures formed a dense cluster with a thickness of about 20 μm. The nanostructures mainly included nanoparticles and nanorods. The oxidation tests found that the SiC nanostructures could significantly improve the anti-oxidation capability of C/SiC composites, particularly, at the temperature beyond 900 °C. The improvement of the anti-oxidation capability of the C/SiC composites was attributed to the formation of a silica layer.

A new type of separator for lithium-ion batteries (LIBs) has been developed using ultrathin micrometer-sized sodium borosilicate glass platelets coated directly on a battery electrode with a water-based binder. The coating process is described in detail, demonstrating coating thicknesses of the glass separator of less than 50 µm. The high-temperature stability has been investigated and it has been shown that the separator is dimensionally stable to at least 600 °C. With regard to the electrochemical performance, full-cell tests on graphite || lithium iron phosphate cells showed a very good behavior, according to which comparable properties of the electrode/separator compound to a commercial polymer-based separator were achieved. This glass separator/electrode composite shows an interesting property profile and is a temperature-stable alternative to conventional polymer-based separators.

Fiber spraying processes are used in the production of fiber reinforced composites, but are performed mainly manual. Given various possibilities for automating such processes, only a few are suitable for the production in small and medium-sized enterprises. We present an approach on robot-based automation of fiber spraying processes. This approach is characterized by its easy programmability of the robot system using the playback programming paradigm. We simulated the reachability and accessibility of our robot-based automation approach and present our prototype system, which can be used for the production of small batches of fiber-reinforced composites.

In this work, a novel building insulation system implying wooden fiberboards and intermediate air layers with highly reflective interfaces for the reflection of longwave IR radiation is introduced. A wall test sample with a double air insulation layer has been built and experimentally investigated in a dedicated setup, which consists of a differential climatic chamber to simulate different indoor and outdoor conditions. The test results have been utilized in validating the developed simulation model. In addition, a thorough numerical parameter study has been conducted, through which the general design rules of the introduced insulation system for realizing the lowest possible effective thermal conductivity have been defined. Furthermore, a multi-air-layer-insulation concept is developed, and the energy saving potential is evaluated. It turned out that, emissivity, object size and air layer thickness are the most dominant design parameters which influence the thermal conductivity of the introduced insulation. A thermal conductivity of 0.033 W/(mK) has been estimated for a multi-air-layer insulation with 7 layers. The obtained results prove the high insulation potential of the introduced building insulation system compared with insulating materials available in the market while outlining their limitations.

Carbon/Carbon (C/C) composites derived from the thermoplastic polymer polyetherimide (PEI) were pyrolized up to 1000 °C, subsequently carbonized in inert atmosphere up to 2200 °C and afterwards infiltrated with liquid silicon. The investigation of fibers and matrix with Raman microspectroscopy revealed, that an increased carbonization temperature leads to an increased carbon order as well as an incipient stress-induced graphitization of the carbon matrix close to the fiber surfaces at 2200 °C. The derived C/C-SiC samples show a maximum flexural strength of 180 MPa with C/C composites treated at 2000 °C and monotonically increasing Young’s moduli ranging from 49 GPa with C/C preforms treated at 1600 °C up to 59 GPa after carbonization at 2200 °C. The carbon fiber strength was evaluated with a single fiber tensile test, which showed a monotonically increased Young’s modulus and a decrease of the strength after carbonization at 2200 °C.

In order to improve the fracture toughness of ZrB 2 ceramics, as-received and heat treated short carbon fiber reinforced ZrB 2 -based composites were fabricated by hot pressing. The toughening effects of the fibers were studied by investigating the relative density, phase composition, microstructure and mechanical properties of the composites. It was found that the densification behavior, microstructure and mechanical properties of the composites were influenced by the fibers’ surface condition. The heat treated fiber was more appropriate to toughen the ZrB 2 -based composites, due to the high graphitization degree, low surface activity and weak interfacial bonding. As a result, the fracture toughness of the composites with heat-treated fiber is 7.62 ± 0.12 MPa m 1/2 , which increased by 10% as compared to the composites with as-received fiber (6.89 ± 0.16 MPa m 1/2 ).

The SiC nanofibres with a length of few millimetres were synthesized successfully on carbon fabrics using a catalyst-free method. The Si and SiO2 powder mixtures functioned as a source for the generation of gaseous species. Following the chemical vapour reaction route, abundant SiC nanofibres with near stoichiometric composition and high crystallinity were grown on the surfaces of carbon fibres. The phase, morphology and crystal structure were characterized to reveal the nucleation and growth mechanism. SiC nanofibres presented a pagoda structure, which is a consecutive stacking of hexagonal segments with a high density of stacking faults. Combining the fabrication process with an analysis of the morphology and crystal structure, both the vapour–solid mechanism and the screw dislocation-driven mechanism are responsible for the nucleation and the growth of SiC nanofibres in the current study. The significant advantage of the present process is that it can be conveniently implemented and provides an approach to allow the fabrication of SiC nanostructures on a variety of carbonaceous substrates without the assistance of a catalyst, leading to less expensive, long length and high purity production of nanostructures.

The residual tensile strength (RTS) evolution of a chemical vapor infiltration and liquid silicon infiltration based 2.5 dimensional reinforced C/C-SiC (2.5D C/C-SiC) composites after fatigue loadings has been investigated. The results show that the fatigue limit (106 cycles) of the 2.5D C/C-SiC composites reaches 58.2 MPa, which corresponds to 75% of the virgin static tensile strength (77.7 MPa). Moreover, an ultimate strength enhancement is observed after fatigue loading. The most pronounced RTS increases to 92.5 MPa when specimens are subjected to fatigue stress of 69.3 MPa for 105 cycles. The microstructural analysis indicates that RTS after cyclic loading is affected by the formation and propagation of cracks and interfacial degradation. Furthermore, a model proposed in this work can well evaluate the RTS of the composites in relation to the number of the applied fatigue cycles.

Ultra-high temperature ceramics are potential materials for a variety of high temperature applications because of excellent thermo-mechanical properties and oxidation resistance. To further improve their fracture properties, a novel colloidal process was proposed to fabricate the short carbon fiber-toughened ZrB 2 –ZrSi 2 composites. Microstructure analysis found that the colloidal processing route could avoid the fibers' agglomeration and alleviate the fibers' damage, which minimizes the structural defects and retains the fibers' strength. The relative density of composites achieves 98.35% and the distribution of fibers in matrix is homogeneous. Mechanical tests indicate that the flexural strength is 458 MPa and the fracture toughness is 6.9 MPa·m 1/2 . In comparison to the composite obtained by conventional processing route, the fracture toughness increases by 47%. The main mechanisms for improved fracture properties could be attributed to the crack deflection, fiber sliding and fiber bridging.

An experimental investigation was performed to study the influence of fatigue damage introduced by different loading cycles on the residual tensile strength (RTS) of plain-weave reinforced C f /C-SiC composites (2D C/C-SiC). The specimens were subjected to the fatigue stress of 57 MPa for the preselected numbers of cycles as follows: 10 2 , 10 4 and 10 5 , respectively, before the static tensile test. The microstructures and fractured surfaces after the tensile test were examined by optical and scanning electron microscopy, respectively. The results showed that the RTS of the specimens after the preselected fatigue cycles numbers of 10 2 , 10 4 and 10 5 increase to 89.8, 94.1 and 82.4 MPa, respectively, which are somewhat higher compared to the virgin samples (79.7 MPa). Additionally, we found that the linear part of the tensile stress-strain curve is independent on the fatigue cycles. Finally, the increased fatigue damage in C/C-SiC composites could determine a reduction of elastic modulus in all cases of fatigue tests.

The fatigue behavior of plain-weave C f /C–SiC composites prepared by liquid silicon infiltration (LSI) was studied under cyclic tensile stress at room temperature. The specimens were loaded with stress levels of 83% and 90% of the mean static tensile strength for 10 5 cycles. The cross-sections and fracture surfaces of the fatigued specimens were examined by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. The results show that the specimens can withstand 10 5 fatigue cycles with a stress level of 90% of the static tensile strength. The retained strengths after fatigue for 10 5 cycles with stress levels of 83% and 90% are about 19% and 11% higher than the static tensile strength. Due to the observation of the microstructures a relief of the thermal residual stress (TRS) caused by stress-induced cracking is probably responsible for the enhancement. Furthermore, the fracture surfaces indicate that the fatigue stress results in interfacial debonding between the carbon fiber and matrix. Additionally, more single-fiber pull out was observed within the bundle segments of fatigued specimens.

Efficient joining materials and techniques are of critical importance for the integration of CMCs in high performance structures. Continuous oxide fiber Nextel™ 610/alumina-zirconia composites were successfully joined to themselves by using a novel glass-ceramic based on the SiO2-CaO-Al2O3-MgO-Y2O3-ZrO2 system.Crystallization kinetic of the novel glass-ceramic was studied using Matusita, Sakka and Ozawa equations. Single lap off-set shear tests and four-point bending tests were performed at room temperature and at 850 °C to investigate the mechanical strength of the joints. Thermal ageing was performed at 850 °C for 100 h in air to check the thermal stability of the joined components. The results showed that the joints were oxidation resistant and the joined interfaces were well bonded. Single lap off-set shear tests on joined samples resulted in delamination of the composites. The average flexural strengths of the joined samples were 71 MPa and 81 MPa, at room temperature and at 850 °C, respectively.

In this work, the development of a novel thermal barrier coating system based on polymer-derived ceramics, applied by simple lacquer methods is reported. The system consists of a polysilazane (PHPS) bond-coat and an insulating layer formed by the combination of passive (YSZ) and active (ZrSi2) fillers with a (organo)silazane (Durazane 1800). The aim of this study is to investigate the influence of type and amount of the different fillers on the coating formation and properties, as well as to obtain high thickness, strong adhesion and low thermal conductivity. The resulting coatings and their components were investigated by TGA, XRD, SEM, and EDX. The adhesion was analyzed by cross-cut tape test and by pull-off test. The thermal conductivity was measured by 3ω-method. The best coating system presents thermal stability up to 1000 °C, thickness of 50 μm, pull-off adhesion of 10 MPa and outstanding low thermal conductivity of 0.44 W (m K)−1.

A simple method was developed for the synthesis of SiC nanowires on a large scale, where the graphite plate and Si–SiO 2 powder mixture were used as the substrate and raw materials, respectively. By this method, pure and high crystalline beta SiC nanowires can be synthesized on the graphite substrate without catalyst. According to the characterization results of XRD, FE-SEM and TEM, it was found that the synthesized nanowires are grown along the [111] orientation and have high crystallinity, clean surface and uniform diameter. And also, it was demonstrated that this method possesses some advantages, such as, low cost and high yield.