Papers by Keyword: Ceramic Matrix Composite (CMC)

Abstract: Carbon fibre reinforced carbon composites (C/C) are characterised by their excellent thermal, chemical and mechanical properties. The intrinsic porosity and fibre reinforcement grant them an excellent damage tolerance. The production of complex structures is time consuming and very expensive. An innovative approach to this topic is the integration of simple geometric ceramic composite materials within complex polymer structures. The motivation of this contribution is to investigate the influence of hexamethylenetetramine as hardener (hardener content: 4, 8, 12 and 16 %) and curing parameters (tempered and non-tempered) on the microstructure and mechanical properties of the porous C/C composites. During the course of this contribution, selected carbon fibre reinforced polymer (CFRP) composites with different porosities were produced while adjusting the resin or hardening agent-ratio, as well as the processing parameters. Subsequent to the curing of the CFRP samples, porous C/C composites were produced by means of a pyrolysis process. The final part of the contribution is comprised of the microstructural analysis by light microscopy and the explanation of the flexural strengths, by utilising a “three-point-bending test”.

Abstract: In this study, it was tried to develop a process chain for ceramic injection molding of Al₂O₃-chopped-fiber reinforced oxide-ceramic-matrix-composite. The feedstocks are compounded at 50 Vol. % filling degree of solid (Al₂O₃ μ-powder (Taimei Chemicals Co. Ltd.) and 3,2 mm chopped fibers (3M)), in which fiber content varies from 0 Vol. % to 100 Vol. %. As binder system, PE + Paraffin Wax + Stearic Acid are used. The ingredients are compounded in a kneader (Brabender) at 125°C and after the viscosity measurement in the high pressure capillary rheometer at 160°C and certain shear rates, the feedstock is injection molded (Battenfeld) at 160°C, which is followed by debinding process, including chemical (in n-Hexane) and thermal steps, and 2h sintering at different temperatures. Flow paths in the machinery parts, rheological properties of binding system, fiber content and the fiber orientation have significant effect on the flow behavior of the feedstock, fiber -orientation, -distribution & -length, which are crucial to understand the properties of end-parts like mechanical reinforcement of the fibers. The fibers in the sintered parts are ca. 200 μm in average length. The fibers in the feedstock show different orientations depending on the part-geometry and the green bodies have different densities depending on sintering temperature, amount of dispersant and fiber orientation.

Abstract: Z-pins reinforced 2D ceramic matrix composites (CMCs), integratedly designed new materials, are developed to enhance 2D CMCs through-thickness in the form of Z-pins and to ensure significant increase in interlaminar fracture toughness, delamination resistance and impact resistance, and Z-pins reinforced 2D CMCs have much application. A manual pre-stitching method is developed to make holes in the graphite fixture to control Z-pins row spacings and to introduce yarns of 3000 T300 carbon fibers bundle into a preform. Z-pins reinforced woven CMCs for research were manufactured successfully by repeatedly using chemical vapor infiltration (CVI) to infiltrate SiC matrix into woven preform and carbon fiber sutures. It is shown that this method of manufactured Z-pins reinforced woven CMC is feasible.

Abstract: The research on ceramic matrix composites and their applications in aerospace field were discussed in terms of their advantages and features, fabrication methods, domestic and foreign research progress, difficulties and key technologies to be solved, and future development trends and directions.

Abstract: Active metal brazing of a new high thermal conductivity SiC-polycrystalline fiber-bonded ceramic (SA-Tyrannohex™) has been conducted using a Ti-containing Ag-Cu active braze alloy (Ticusil®). The brazed joints were characterized using SEM-EDS and Knoop hardness scans across the interfaces. The effects of fiber orientation in the composite on the microstructure, elemental composition, and microhardness are presented. Results show that this material can be successfully joined using judiciously selected off-the shelf active braze alloys to yield metallurgically sound joints possessing high integrity.

Abstract: Sol-Gel technology was used to develop carbon, silicon and oxygen based ceramics as well as their composites with Carbon fiber and nano siliconcarbide as reinforcements. Gels with different composition were prepared from TEOS, HMDSO and DEDMS. Dried gels were post-cured in air and pyrolyzed at 1000oC in nitrogen atmosphere. Each step of sol-gel process was characterized for density, thermal behaviour and functionality. Composites were prepared using different sols (derived from TEOS, HDMSO and DEDMS) as matrix precursors and carbon fabric as reinforcement. To some composites another phase of solid, micro/nano powder precursor of SiC was added to decrease number of impregnation cycles. Latter composites resulted in higher density. Green composites were post-cured and pyrolyzed. These composites were characterized for density and microstructure. It revealed that the resulting matrix was solid glasses and addition of SiC powder facilitated the rapid densification. Composites prepared with SiC nanparticles as well as Carbon fabric as reinforcement exhibit higher flexural strength than those made without nanoparticles. The fracture behaviour is also seen to be of mixed mode failure type.

Abstract: Z-pins reinforced 2D ceramic matrix composites (CMCs), integratedly designed new materials, are developed to enhance 2D CMCs through-thickness in the form of Z-pins and to ensure significant increase in interlaminar fracture toughness, delamination resistance and impact resistance, and Z-pins reinforced 2D CMCs have much application. Finite element method was adopted to analyze stress distributions of Z-pins reinforced woven CMCs; the interlaminar shear tests were employed to measure interlaminar shear strength; fractographies were observed to examine failure mechanisms. The results are shown as the following: the insertion of Z-pins reduces concentrated stress fields and enhances the uniform stress distribution on the expected fracture plane. Interlaminar shear strength of Z-pins reinforced woven CMCs is increased as Z-pins insertion reaches a certain number. Interlaminar shear strength goes up with the rise of the number of inserted Z-pins. Z-pins shearing and fabric/matrix debonding are interlaminar failure mechanisms of Z-pins reinforced CMCs.

Abstract: Two composites of 2D C/SiC-C and 2D C/SiC were fabricated by isothermal-isobaric chemical vapor infiltration (ICVI). The microstructures and mechanical behaviors at room temperature were characterized and investigated, respectively. In the 2D C/SiC-C composite, the PyC matrix layers are homogeneous and continuous. Moreover, the matrix layers of SiC and PyC bond well and almost no microcracks are found in the multilayered matrix. Compared with the 2D C/SiC composite, the 2D C/SiC-C composite exihibits improved mechanical properties.The successive extraction of matrix layers and multiple deflections of cracks in the SiC/PyC multilayered matrix contribute to the improvement of mechanical properties.

Abstract: Mullite–zirconia composites were synthesized through reaction sintering Algerian kaolin, α-Al2O3, and ZrO2. Phases present and their transformations were characterized using x-ray diffraction. Quantitative phase analysis was performed following the Rietveld method. Hardness and fracture toughness were measured by Vickers indentation. The flexural strength was measured using a Universal Testing Machine. It was found that the microstructure of samples sintered for 2 hours at 1600°C was composed of mullite grains which have whiskers’ shape and ZrO2 particles. In the composite containing 16 wt.% ZrO2, the ratio of tetragonal zirconia transformed to monoclinic zirconia was relatively small and did not exceed 18%. However, in the composite containing 32 wt.% ZrO2 around 75% of the tetragonal structure changed to monoclinic structure. Also, it was found that the increase of ZrO2 content from 0 to 32 wt.% decreased the microhardness of the composites from 14 to 10.8 GPa. However, the increase of ZrO2 content from 0 to 24wt.% increased the flexural strength of the composites from 142 to 390 MPa then decreased it with further increase of ZrO2 content. The fracture toughness increased from 1.8 to 2.9 MPa.m1/2 with the increase of ZrO2 content from 0 to 32 wt.%; and the rate of the increase decreased at higher fractions of ZrO2 content. The average linear coefficient of thermal expansion (within the range 50 to 1450°C) for samples containing 0 and 16 wt.% ZrO2 sintered at 1600°C for 2 hours was 4.7 x10-6 K-1 and 5.2 x 10-6 K-1 respectively.

Abstract: To understand the creep damage mechanism of a standard 3D Carbon fiber reinforced silicon carbide composite (C/SiC) in high temperature combustion gas at 1300 °C, the creep tests were carried out in a combustion wind tunnel and the mechanisms were investigated by the extension of specimens and the microstructure of fracture section. It was found that the external tensile load was bore by the carbon fibers in the active region during the stressed oxidation process. The oxidation mechanisms of the active region were determined by a normalized threshold stress. Below the normalized threshold stress, the oxidation was controlled by internal diffusion of oxidizing gases through microcracks in SiC matrix. Above the normalized threshold stress, the oxidation was controlled by the reaction of carbon fiber with oxygen and water vapor.