Itsaso Echeverria is an Engineering Doctorate (EngD) student working on the development of manufacturing techniques for complex-shaped oxide/oxide Ceramic Matrix Composites (CMCs). She obtained a Masters degree at University of Basque Country (Spain) in Materials Science and joined the National Composites Centre (NCC) in 2016 working on the development of characterisation methods for polymer matrix composites for sectors such as aerospace, automotive or energy. In October 2017, she started an EngD project on CMCs with the University of Surrey, jointly funded by the NCC and the Engineering and Physical Science Research Council.
Ceramics are used for high temperature applications such as thermal barriers and components in high efficiency engines, due to their refractoriness and sustained mechanical properties at elevated temperatures. Conventional ceramics are inherently brittle with a low fracture toughness compared with metals. To overcome this, ceramic whiskers or continuous fibres are added to ceramic matrices, forming ceramic matrix composites (CMCs). CMCs have the advantages of a higher fracture toughness than monolithic ceramics whilst retaining a lower density compared with metals such as nickel superalloys used in similar applications. They can also have excellent corrosion/oxidation resistance properties in harsh environments. These attributes make them highly suitable as substitutes for metals in high temperature applications and in particular within the aerospace sector.
Currently the processing of CMCs carries a high manufacturing cost in comparison with metal alloys. This is due to the high energy-intensity of the process which limits the use of CMCs to high-end applications. The high cost of the fibres comes from the preparation of the bulk material to be spun, spinning it to form the green fibre and then heat treating it to obtain the ceramic fibre. During the manufacturing process, specialised equipment is required, in addition to high purity, and hence expensive, ceramic powder and long cycles at high temperatures to heat treat the fibres. Furthermore, in order to process ceramic matrix composites a suitable atmosphere is needed during the sintering stage, in particular for non-oxide CMCs for which the presence of oxygen is not favourable. As a result, there is interest in investigating whether processes and techniques that are used with polymer matrix composites (PMCs), can be adapted for use with CMCs to drive costs down. Additionally, the aerospace industry is already familiar with the methods and equipment used with PMCs, hence it will be very beneficial to transfer the knowledge from PMCs to CMCs.
The use of manufacturing methods commonly used for polymer matrix composites (PMCs) in the production of ceramic matrix composites (CMCs), as opposed to more traditional ceramic manufacturing methods, has the potential to reduce the cost of components. This work focuses on three typical PMC manufacturing methods and assesses their suitability for the production of an oxide-oxide porous matrix ceramic composite, starting from a commercially available pre-impregnated Nextel 610®/aluminium oxide material. While all the techniques can be used to produce CMCs, results showed that compared with vacuum bagging and warm pressing, autoclave processing produced the best outcome. It resulted in the most uniform thickness laminates and the lowest macro-porosity, as well as the highest flexural strength.