Made to Measure…Silicon Carbide Monofilaments

Who are you? Michael Rix

What is your role? EngD Research Engineer

What is your work about? Silicon Carbide Monofilaments for the Reinforcement of Titanium Metal Matrix Composites

I beg your pardon? Silicon carbide monofilaments are continuous fibres that are about as thick as a human hair and several kilometres in length. They are extremely strong, even at high temperatures, but like all ceramics they are brittle and therefore difficult to use in structural applications. Reinforcing titanium with these monofilaments takes advantage of the ceramic’s properties to produce a composite that is both stronger and lighter than monolithic titanium. Figure 1 shows a cross-sectioned composite with the fibres in a hexagonal array. My doctoral research with the University of Surrey and TISICS has been focussed on the development and characterisation of the monofilaments.



Figure 1 – A secondary electron image of a metal matrix composite panel.  Note the bright dots in the centre of the fibres, which are the tungsten wire precursor on which the SiC is deposited by chemcial vapour deposition (CVD).

Why? Lightweight, high strength materials are desirable in many industries. In aerospace in particular reducing weight is always a priority for improving efficiency. Ceramics theoretically have extremely high specific strength but in practise they often fail to achieve this due to the wide range of defects that occur during their production. They are also difficult to incorporate into complex structures due to their brittle nature. The silicon carbide monofilaments produced at TISICS have a very narrow strength distribution as a result of a carefully controlled chemical vapour deposition (CVD) process. While the monofilaments are still brittle it is possible to design composites to take advantage of their strength while protecting them from damage by exploiting the toughness of the metal matrix.

And? My research looks at improving the CVD process by reducing its complexity and optimising the rate of production. The simplest metal matrix component requires several kilometres of monofilament—as much as possible of which should be made in a single length with no defects. I am also investigating the microstructure of the monofilament coating, which is important to the performance in composite.

So what? When the monofilaments are produced correctly, the resulting metal matrix composite exhibits double the strength of the equivalent titanium alloy with a reduction in density of up to 40%. Additionally, because it is possible to change the volume fraction of monofilaments within the matrix the properties of the composite can be tailored to specific design requirements.

Final Thought: Made to measure metal matrix composites using these silicon carbide monofilaments exploit the best properties of ceramics and metals to produce high performance composites for jet engines, air frames, landing-gear and pressure vessels.