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.

Creep behaviour of a SiC/Si-B-C composite with a self-healing multilayered matrix

Abstract: The creep behaviour of a SiC/Si-B-C composite at 1200 °C in argon is investigated under static and cyclic loading conditions. The SiC/Si-B-C composite consists of a multilayered self healing matrix reinforced with Nicalon fibers. It was produced via chemical vapor infiltration (CVI). The creep behaviour is examined with respect to the extent of damage created during an initial step of monotonic loading and controlled through the applied strain. The creep rate is shown to be dictated mainly by creep of fibers and interfacial debonding, whereas no significant creep induced matrix cracking was detected.

Influence of grit geometry and fibre orientation on the abrasive material removal mechanisms of SiC/SiC Ceramic Matrix Composites (CMCs)

Abstract: SiC/SiC Ceramic Matrix Composites (CMCs) have been identified as a key material system for improving aero engine performance as they offer low density, high strength and stiffness, and superior environmental resistance at high temperatures. Nevertheless, due to their heterogeneous, hard and brittle nature, these materials are considered among the most difficult-to-machine, and grinding arises as one of the preferred choices for their processing. Therefore, understanding of the material removal mechanism and influence of the abrasive grit geometry when grinding CMCs is a critical enabler for achieving high component quality at highest efficiency and minimum cost. With the aim to reduce the uncertainties associated with the stochastic nature of the abrasive particles, grits of different shapes and sizes have been accurately created by Pulse Laser Ablation (PLA). In order to reproduce the grinding process kinematics, scratch tests in a circular trajectory have been carried out with single abrasive grain with different geometries and sizes, and arrays of overlapped grains to determine the influence of shape, size and spacing on the surface integrity of SiC/SiC CMCs after grinding. The morphology of the various constituents of the workpiece has been assessed regarding the direction of the scratch with respect to the orientation of the fibres. Results reflect a higher influence on the process forces by the grain shape rather than fibre orientation. Moreover, after the inspection of the abraded individual CMC constituents, a change in the mechanisms governing the process for the different abrasive grain geometries have been identified, despite the brittle material removal mode displayed by all of them. Explanation of the ground surface morphology in an analytical and comprehensive manner through a contact mechanics approach shows that the crack onset location is governed by the grains shape but its direction of propagation depends on the fibre orientation.

Turbine components with thermal barrier coatings

Abstract: A turbine component has a substrate formed from a ceramic material selected from the group consisting of a monolithic ceramic material and a composite ceramic material and a thermal barrier coating bonded to the substrate. In one embodiment, the ceramic material forming the substrate is selected from the group of silicon nitride and self-reinforced silicon nitride. In another embodiment, the ceramic material forming the substrate is selected from the group consisting of a silicon carbide-silicon carbide material and a carbon-carbon material. At least one bond coat layer may be interposed between the substrate and the thermal barrier coating.

Surface Conditioning Protocol for the Adhesion of Resin-based Materials to Glassy Matrix Ceramics: How to Condition and Why?

Abstract: Question: What is the best surface conditioning protocol for durable adhesion of resin-based materials to glassy matrix ceramics? Answer: Glassy matrix ceramics, also known as silicabased ceramics, are typically reinforced with feldspar, leucite, fluormica glass or lithium disilicate. Glass ceramics are acid sensitive when etched with hydrofluoric acid gel and they respond well to adhesive bonding techniques where silanization and adhesive resin applications are performed. In such ceramics, more pronounced surface roughness can be obtained with the increase in the amount of glassy phase present in the microstructure, which can improve the potential adhesion of resin-based luting cements to these ceramics. Proper conditioning of glass ceramics together with the subsequent application of the adhesive procedures not only enables fabrication of minimally invasive restorations, but also reinforces the vitreous matrix, increasing its strength after adhesive cemention. Since the type of ceramic matrix, etching method, silanization, and adhesive resin application are important parameters in durable adhesion to glass ceramics, the surface conditioning sequence presented in the Table (below) is recommended.

Designing Interfaces in Inorganic Matrix Composites

Abstract: The key to controlling and predicting the properties of metal matrix composites lies in understanding and controlling the interface. When properly designed, the interface between reinforcing fibers and the matrix or protective coating can act as a mechanical fuse through a controlled delamination mechanism. Controlled delamination, in effect, results in the decoupling of fibers from early damage due to stress concentrations in the vicinity. The delamination event must precede the crack bridging and frictional pull-out mechanisms that have been so effectively demonstrated in ceramic matrix composites. The delamination event, therefore, is the necessary precondition, and so analysis of composite toughening must start with a definition of the conditions for interface debonding. This decoupling can be expressed in terms of cohesive strength of the interface, shear strength of the interface, and fiber fracture stress. In a related but alternative manner, debonding can be expressed in terms of the intrinsic work of fracture of the interface as compared to the transverse work of fracture of the fiber.