Papers by Keyword: Ceramic Matrix Composite

Abstract: The article considers issues related to the choice of abrasive material and technology of its use for the formation of necessary roughness on the base material and necessary heat resistance of the heat-protective coating during plasma spraying. The influence of the shape and size of the abrasive on final roughness of the treated surface was studied at various angles of contact between the sprayed abrasive and the surface (angle of attack). From the condition of maximum heat resistance, the composition of the heat-resistant composite coating of the spinel type was determined, which consists of 3 layers: the 1st layer (sublayer) material is a chromium-aluminum composite and the 2nd layer of a transitional spinel-based aluminum and chromium oxide + chromium-aluminum composite and the 3rd a layer of spinel based on aluminum and chromium oxides.

Abstract: A model of the transition layer between the shell and the core of a ceramic matrix composite from coal waste and clay has been developed. The chemical, granulometric and mineral compositions of the beneficiation of carbonaceous mudstones and clay were studied. The technological and ceramic properties of raw materials for the samples manufacturing were determined. The method of manufacturing multilayer ceramic samples from coal waste, clay and their mixture is given. The number of transition layers in the contact zone between the clay shell and the core from coal wastes is determined. The deformation and swelling phenomena of model samples from coal wastes, clay, and their mixtures were revealed at the firing temperature of more than 1000 °C. The formation of a reducing ambient in the center of the sample with insufficient air flow is shown. The influence of the carbonaceous particles amount and the ferrous form iron oxide in the coal wastes on the processes of expansion of multilayer samples during firing has been established.

Abstract: The increasing market share of highly volatile electricity generated from renewable sources like wind or solar energy, leads to enormous challenges in the energy sector. Since large-scale storage systems are neither currently nor in the near future available, the gap between electricity from renewable sources and current electricity demand has to be closed with flexibly operated conventional power plants. In order to be a viable, cost-effective option in tomorrow’s energy market future power plants must be highly efficient while having low CO₂ emissions. Furthermore, they have to be highly reactive to counter instabilities in the electrical grid due to fluctuations in renewable sources. Current materials used in power plants are only within limits suited to experience extreme changes in operational loads. However, extreme changes of operational loads will become increasingly severe with a growing share of renewables. Our project team has developed a new concept for CMC-jacketed pipes to alleviate these issues. Recently, this concept was further developed and tested in laboratory as well as a large-scale application test at Grosskraftwerk Mannheim (GKM). All tests are still ongoing. Additionally, to the use in modern highly efficient power plants such CMC-jacketed piping is also suitable for other high-temperature applications, like e.g. solar power plants or industrial chemical applications.

Abstract: Ceramic matrix composites (CMCs) are known to have high hardness, temperature and corrosion resistance, while being comparatively lightweight. One of many external factors that influence the mechanical properties of CMC is the compaction pressure given during fabrication process. Generally, greater amount of applied compaction pressure will result in improved final product density and bending strength. In this research, a type of CMCs was fabricated using Al₂O₃, SiC, and ZrO₂ powder mixed with Nb₂O₅ additive of 81Al₂O₃-10SiC-5ZrO₂-4Nb₂O₅ wt. % composition. Fabrication was done through mixing, compacting, and sintering process. Compaction was performed at 257, 308, and 359 MPa and finished with sintering process at 1400 °C for 4 h. Final samples were characterized by density measurement, 3-point bending strength testing, XRD for phase investigation, and microstructure observation using SEM-EDS. Results showing that samples with 308 MPa compaction pressure possessed the highest density and bending strength of 3.29 gr/cm³ and 14.91 MPa, respectively. These numbers however, declined on samples with higher compaction pressure of 359 MPa due to the formation of porosities caused by entrapped gas that failed to exit the sample of which compaction pressure was considered to be overwhelmingly high.

Abstract: Achieving an appropriate dispersion of Carbon Nanotubes (CNTs) within a ceramic matrix should be referred to as the main challenge for the synthesis of CNTs reinforced ceramics with enhanced toughening properties. In the present paper, dispersion of 1 wt% MWCNTs within 3YTZP based ceramics has been investigated through the comparison of three conventional approaches based on using surfactants, functionalization, and planetary milling. Addition of 2 wt% Sodium Dodecyl Sulfate (SDS) as the surfactant material followed by 2 hours ultrasonication was found successful to disperse carbon nanotubes in a water media, while chemical functionalization of the CNTs surface using a mixture of H₂SO₄/HNO₃ (3:1) could result in identical well dispersed powder mixtures. Formation of functional groups on the surface of CNTs was confirmed by FTIR spectroscopy and efficiency of the above methods to result in well dispersed powders was detected using UV-Vis spectroscopy. The surfactant method was, accordingly, found to result in the highest dispersion of nanotubes within the ceramic microstructure. In the planetary milling method, well dispersed CNTs within 3YTZP particles could be attained through the optimization of processing conditions such as 24 h milling time, 250 RPM, and 2 BPR. The accuracy of the above results could be verified by SEM as well as Raman spectroscopy. On the other hand, although the dispersed powders provided through functionalization and planetary milling methods revealed CNTs bundles in few scopes of the SEM results and minor damages were also observed in the Raman spectroscopy report, they were both at acceptable levels.

Abstract: The microstructure and crystallographic relationship development of spinel phase of the composite prepared by sintering of Al2O3 and Ni powders below the melting point of Ni was investigated. Spinel phase is distributed not uniformly and the outer region of sample contains Al2O3 and NiAl2O4 without Ni particles. The differences in the microstructure between the central and surface part of the sample was clearly demonstrated. In the central part of the sample this process was only initiated and start of this reaction can be observed at the Ni/Al2O3 interface. This distribution of spinel phase is connected with the process of its formation and stability. Analysis of the crystallographic relationship between the Ni and spinel (S) indicates that the most common is the crystallographic relationship [001] S || [001] Ni or [001] S || [111] Ni. Similarly there is some statistical preference of the crystallographic relationship between spinel and Al2O3. In this case more often observed relationship is [100] S || [111] Al2O3, however similarly as in the case of Ni some deviations of several degrees are also frequent.

Abstract: The oxidation kinetics of SiC fiber-reinforced SiC matrix composites with a BN interphase (SiC/BN/SiC) and the constituent fibers was characterized by thermogravimetric analysis and microstructural characterization at temperatures (816-1538°C) and oxygen partial pressures (0.1% to 5% O₂) relevant to the hypersonic flight and re-entry environments. TGA of the SiC fibers showed that oxidation of the thin BN surface layer led to initially rapid oxidation kinetics and formation of a relatively thick silica scale at very short times under most test conditions. At longer times the fiber oxidation kinetics were representative of silica formation on pure SiC. Oxidation of the composites was conducted on coupons with the SiC seal coat removed on one edge to simulate damage to the composite, allowing ingress of oxygen to the fiber tows. Microscopy was conducted to determine the distance of oxygen ingress into the coupon. At the lower temperatures and oxygen partial pressures the exposed edge did not seal off by silica formation, yet the BN interphase areas were only minimally oxidized. At the intermediate temperatures silica formed at the exposed surface limiting further oxidation of the exposed fibers and BN interphase areas. Finally at the highest temperature and lowest oxygen partial pressure, active oxidation of SiC occurred for both the fibers and coupons resulting in irregular material attack. Implications for use of SiC/BN/SiC materials for hypersonic vehicle thermal protection systems are summarized.

Abstract: Alumina (Al₂O₃) matrix composites reinforced with 10%, 20% and 40% of 10µm size aluminum particles were fabricated by two processes, namely cold pressing and sintering process and Sol-Gel process. Al2O3, Al, 5% volume fraction of cobalt was mixed together, compacted and then sintered at 400-500oC for 30 minutes to fabricate the CMC. In the Sol-Gel fabrication route the Al₂O₃, Al, Co were blended with water and aged for 2-3 days to remove all the moisture and to enable oxidation of Al reinforcement. The mixture was cold pressed and sintered at 400-500oC to produce the CMC. The composition analysis of the CMC carried out by EDAX clearly showed that Al₂O₃ particles were formed by oxidation of Al reinforced in the matrix, effectively forming Al₂O₃/Al₂O₃ particulate reinforced ceramic matrix composite. The nature of the bonding at the interface was characterized using Scanning Electron Microscopy (SEM). The amount of porosity was determined using image analyzer based on ASTM B 276 standard. The average micro hardness of the samples was measured. The optimum volume fraction of aluminum for better interface bonding and reduced porosity was determined using the results obtained.

Abstract: Continuous carbon fiber reinforced silicon carbide composite material (C/SiC) is one of the most effective candidate materials for hot structures in aeronautic and aerospace applications. Its performances in the complicated service environments are widely concerned. A database, aiming at optimized design of C/SiC, was developed. The database collected original data on the fabrication, microstructure of C/SiC, as well as abundant data on performance experiments including tension, compression, shear, fatigue, creep, oxidation, high-temperature fatigue, and so on. The logic structure of the database, modeled by unified modeling language, provides a data link that connecting the processing, microstructure and performance of C/SiC, so that users can conveniently create a test result set to build the mathematical model of material design. Efficient software was developed to realize management, browsing and extension of the database.

Abstract: Si₃N₄-Ti(C,N) nanocomposites fabricated by vacuum hot pressing with Al₂O₃ and Y₂O₃ as additives were investigated. The results showed that the α-Si₃N₄ phase converted completely into whisker-shaped β-Si₃N₄ grains after vacuum sintering at 1700°C. Suitable addition and well dispersion of the Ti(C,N) particles can restrained the lateral growth of the β-Si₃N₄ grains, increasing aspect ratio of the β-Si₃N₄ grains and improving bending strength of the composites. Fracture toughness of the composites is higher than that of the β-Si₃N₄ ceramics, and the main toughening mechanism is crack bridging due to the higher aspect ratio of the β-Si₃N₄ grains.With the addition of 1vol% of Ti(C,N), the composite has a relative density of 99.31%, Vicker’s hardness of 15.9 GPa, bending strength of 993 MPa, and fracture toughness of 9.9 MPa·m^1/2.