Ceramic matrix composite

About: Ceramic matrix composite is a research topic. Over the lifetime, 7807 publications have been published within this topic receiving 117020 citations.

Ceramic matrix composite structure having integral cooling passages and method of manufacture

Abstract: A multi-layer ceramic matrix composite structure (40) having a plurality of fiber-reinforced cooling passages (42) formed therein. The cooling passages are formed by the removal of a fugitive material. The fugitive material is part of a wrapped fugitive material structure containing a layer of reinforcing ceramic fibers (26) that is used to lay-up the multi-layer structure. An intermediate layer of ceramic fabric may be placed alternately over and under the wrapped fugitive material structure to separate the cooling passages into alternating upper and lower cooling passages. The transversely oriented fibers surrounding the cooling passages serve to increase the interlaminar strength of the structure when compared to prior art designs. An airfoil member incorporating such reinforced integral cooling passages is provided.

Stress-Dependent Matrix Cracking in 2D Woven Sic-Fiber Reinforced Melt-Infiltrated Sic Matrix Composites

Abstract: The matrix cracking of a variety of SiC/SiC composites has been characterized for a wide range of constituent variation. These composites were fabricated by the 2-dimensional lay-up of 0/90 five-harness satin fabric consisting of Sylramic fiber tows that were then chemical vapor infiltrated (CVI) with BN, CVI with SiC, slurry infiltrated with SiC particles followed by molten infiltration of Si. The composites varied in number of plies, the number of tows per length, thickness, and the size of the tows. This resulted in composites with a fiber volume fraction in the loading direction that ranged from 0.12 to 0.20. Matrix cracking was monitored with modal acoustic emission in order to estimate the stress-dependent distribution of matrix cracks. It was found that the general matrix crack properties of this system could be fairly well characterized by assuming that no matrix cracks originated in the load-bearing fiber, interphase, chemical vapor infiltrated Sic tow-minicomposites, i.e., all matrix cracks originate in the 90 degree tow-minicomposites or the large unreinforced Sic-Si matrix regions. Also, it was determined that the larger tow size composites had a much narrower stress range for matrix cracking compared to the standard tow size composites.

Cyclic Fatigue of Ceramics: A Fracture Mechanics Approach to Subcritical Crack Growth and Life Prediction

Abstract: Cyclic fatigue, and specifically fatigue-crack propagation, in ceramic materials is reviewed both for monolithic and composites systems. In particular, stress/life (S/N) and crack-propagation data are presented for a range of ceramics, including zirconia, alumina, silicon nitride, SiC-whisker-reinforced alumina and a pyrolytic-carbon/graphite laminate. S/N data derived from unnotched specimens often indicate markedly lower lives under tension-compression compared to tension-tension loading; similar to metals, 108-cycle “fatigue limits” generally approach -50% of the tensile strength. Crack-growth results, based on studies on “long” (>3mm) cracks, show fatigue-crack propagation rates to be markedly power-law dependent on the applied stress-intensity range, ΔK, with a threshold, ΔKTH, of the order of -50% of Kc. Conversely, for “small” (<250μm) surface cracks, fatigue-crack growth is seen to occur at ΔK levels some 2 to 3 times smaller than ΔKTH, and to show a negative depen-dency on applied stress intensity. At ambient temperatures, lifetimes are shortened and crack-growth rates are significantly accelerated by cyclic, compared to quasi-static loading, although limited data suggest the reverse to be true at very high temperatures in the creep regime. Such results are discussed in terms of the primary crack-tip shielding (toughening) mechanisms and potential mechanisms of cyclic crack advance. Finally, implications are discussed of long and small crack cyclic fatigue data to life prediction and safetycritical design of ceramic components.

Preparation and Microstructure of Multi‐Wall Carbon Nanotubes‐Toughened Al2O3 Composite

Abstract: With multi-wall carbon nanotubes (MWNTs) as reinforcement, a 12 vol% MWNTs/alumina (Al2O3) ceramic composite was obtained by hot pressing. A fracture toughness of 5.55±0.26 MPa·m1/2, 1.8 times that of pure Al2O3 ceramics, was achieved. Experimental results showed that the enveloping of carbon nanotubes (CNTs) with sodium dodecyl sulfate (SDS) is effective in changing the hydrophobicity of CNTs to hydrophilicity and improving the dispersion of CNTs in aqueous solution. Enveloped with SDS, CNTs can be homogeneously mixed with Al2O3 at a microscopic level by heterocoagulation. This mixing method can obviously improve the chemical compatibility between CNTs and Al2O3, which is important for enhancement of interfacial strength between them.

Fabrication of reinforced composite material comprising carbon nanotubes, fullerenes, and vapor-grown carbon fibers for thermal barrier materials, structural ceramics, and multifunctional nanocomposite ceramics

Abstract: The present invention is directed towards a ceramic nanocomposite comprising a nanostructured carbon component inside a ceramic host. The ceramic nanocomposite may further comprise vapor grown carbon fibers. Such nanostructured carbon materials impart both structural and thermal barrier enhancements to the ceramic host. The present invention is also directed towards a method of making these ceramic nanocomposites and for methods of using them in various applications.