Oxide ceramic matrix composites - manufacturing, machining, properties and industrial applications

Oxide ceramic matrix composites (O-CMC) combine high temperature stability, low density, high strength and good corrosion resistance with a damage-tolerant quasi-ductile fracture behaviour enabling a variety of applications with demanding thermal and mechanical requirements

Technische Keramiken - Werkstoffe für extreme Bedingungen

In einer Zeit, in der immer leistungsfähigere und effizientere Fortbewegungsmittel entwickelt werden, erschließt die Technische Keramik nach und nach die Luftfahrt. Vor allem textil verstärkte Keramiken, sogenannte ceramic matrix composites (CMC) sollen in Zukunft metallische Bauteile in Turbinen ablösen. Unter anderem forschen hier große Unternehmen wie GE oder die MTU nach Optimierungsmöglichkeiten für diesen spannenden Werkstoff

Oxide ceramic fibers via dry spinning process - from lab to fab

Oxide fibers preparation and manufacturing capabilities at Fraunhofer-Center HTL are introduced, showing the development and preparation of oxide ceramic fibers from lab scale to pilot scale up to near production scale. As a specific example, the development of an aluminosilicate fiber with mullite composition is discussed in more detail. Fiber development started from nonaqueous sol-gel precursors in the early lab scale. With increasing fiber spinning volume, precursors were switched to water-soluble systems. Transformation from green fiber to ceramic fiber was monitored by thermogravimetric and differential thermal analysis, X-ray diffraction, and scanning electron microscopy. The evolution of ceramic phases, microstructure formation, and the effects on tensile strength and Young's modulus were investigated. Weibull statistics and fracture analysis helped to understand the results. Next step will be the transition from large lab scale to pilot scale, demonstrating manufacturing capability

Manufacture and Characterization of Oxide Ceramic Matrix Composites out of Commercial Pre-Impregnated Fabrics

In this work, a recent production technique of oxide ceramic matrix composites with a porous matrix based on commercial prepregs from Axiom, USA, was developed and investigated. The main objectives were to study the influences of the different prepreg types and the manufacturing process on the material properties. Two commercially available prepregs – Nextel™ 720 fabric with alumina-silica matrix based on a non-aqueous slurry and Nextel™ 610 with alumina matrix based on an aqueous slurry – are processed with the simple techniques of laminating, warm pressing, drying and sintering. The manufacturing process has been defined on one hand based on the prepreg manufacturer’s recommended curing cycle as well as based on thermogravimetric analysis. On the other hand, standard-processes from own know-how were used which are based on the wet layup technique with fabrics infiltrated by hand. The manufacturer of the prepreg recommended curing via warm compression or autoclave process. The autoclave process has been pushed aside in order to significantly reduce production costs. The matrix composition has been analyzed after different processing steps. Bending and shear tests showed the influence of the different prepregs and thermal treatment on mechanical properties. Based on experimental results from microstructural analysis and mechanical testing, it was shown that prepregs out of alumina fabric with an aqueous alumina matrix are suitable for the production of the all-oxide CMCs

Hot gas stability of various ceramic matrix composites

This chapter examines the hot gas stability of oxide and non-oxide CMC, fabricated in different institutions of the CCeV in the burner rig of Fraunhofer IKTS Dresden. The tests were performed at 1250 °C and 1400 °C, a gas speed of 100 m/s and a water vapor pressure between 0.2 and 0.25 bar. The chapter also examines microstructure of surface and bulk material after hot gas test in comparison to the as fabricated materials. Various oxide materials were fabricated with hot gas resistant matrix materials, which exhibited superior hot gas stability. Information about the influence of the hot gas test on the mechanical behavior was obtained by comparison of the failure behavior in 3-point bending strength tests on samples prior and after the hot gas test. Embrittlement of the oxide CMC caused by grain coarsening of the ceramic fibers and matrix was observed with increasing test temperature