Selectively anisotropic continuous fibre ceramic composites via slurry injection

Continuous fibre ceramic composites for application in extreme environments is a burgeoning area in materials engineering. The production of sufficiently damage tolerant and reusable materials systems based on high fibre fraction and high dimensionality fibre substructures is widely considered to be a promising area for future refinements. One of these refinements is the ability to functionally grade materials in such a way as to impose a beneficial property gradient throughout a component’s body. This thesis scrutinises a method for producing such anisotropic ceramic composites via injection of ceramic suspensions. The injection method is developed from previous work and literature to investigate the ability to place deposits selectively within a fibre architecture to build up a ceramic composition gradient. A series of such suspensions were formulated and tested to produce a property spectrum. A parametric study was then performed to consider the effects of the physical properties of the fluids – and how they couple with the processing variables on the timescale of the injection – on the shape and growth of the deposits in a particular fibre architecture. This information was then used to produce a set of statistical relations describing the production of deposits, and these were used to determine the viability in producing functionally graded structures within the preform type. The permeation mechanisms were investigated microstructurally, and the fracture behaviour of the composites with reference to ceramic interfaces within a contiguous fibre structure were addressed. It was found that no conditions tested permitted large degrees of control in the deposit growth as defined in the study. Consequently, the ability to produce small-scale functional grading was considered to be minimal. Additionally, the mechanisms for spreading were found to be heavily impacted by the capillary forces in the narrow fibre pores, inferred from both experimental and numerical results. These channels were found to be susceptible to flow channel constriction due to particulate clogging, thus adding complications to flow prediction. However, these conclusions are significantly based on the specific fabric substrate used. The details of the methods used are a useful transferable aspect of this study for the development of functionally graded materials by injection in other substrates. Specimens produced for this study demonstrated fracture patterns that did not necessarily propagate along the ceramic composition interface. This helps reinforce the base premise of this study; a composite produced from grading a continuous reinforcement substructure may retain a fracture pattern insensitive to the ceramic distribution, thus differentiating it from many laminate and coated materials. This conclusion may be applied to those materials that are of interest to this study; Cf/C composites modified by ceramic inclusions