School of Engineering and Materials Science
Research Student Roll of Honours
PhD Thesis: Tape casting as a novel processing route for silicon carbide fibre-reinforced titanium metal matrix composites
Author: LOBLEY, Christopher
Supervisor(s): Xiao Guo
A low-cost technique of manufacturing SiC-reinforced titanium metal matrix composites has been proposed and developed. The process involves: firstly, the formation of a powder slurry with various organic components; secondly, casting of the slurry into a powder tape, which is subsequently laid-up with SiC fibre mats; thirdly, debinding at an intermediate temperature to remove the organics; and finally consolidating the organic-free lay-up into a composite. Relevant facilities to enable the processing of the composites have been designed and developed.
After an initial screening study, a system of organics based on Poly(vinyl butyral) and Benzyl Butyl Phthalate has been shown to give the required slurry and tape properties. The casting speed, slurry viscosity and the height of the doctor blades have been identified as the important parameters for tape casting. Uniform tapes have been produced and characterised in terms of the thickness and the powder volume fraction. The quantity of organics, the slurry forming conditions and the casting parameters have been optimised.
Both thermogravimetry and mass spectrometry have been used to identify the appropriate debinding temperatures and the molecular species evolved during organic removal. It was noted that the removal of plasticiser and binder took place in two well-defined stages. Heavier species could be present at temperatures up to 500°C.
Composite and monolithic specimens have been processed using both Ti-6A1-4V and Ti-15V-3Cr-3A1-3Sn matrices. Under the consolidation conditions studied so far, both reinforced and un-reinforced specimens exhibited some level of matrix porosity. The presence of matrix contamination from the original Ti-6-4 powder was identified to be mainly responsible for some inclusions. Composites based on the Ti-15-3-3-3 matrix have been consolidated by HIPing and possess tensile strengths comparable to published values. Composites based upon both the Ti-6-4 and the Ti-15-3-3-3 matrices exhibit a good fibre distribution and no apparent fibre damage.