Silicon doped boron carbide a lightweight impact resistant material

There is a need for impact resistance light weight materials for a number of applications including, 1) for the aerospace industry, particularly satellites where protection from high speed space debris is required 2) ballistic personal armour. In this case, high quality light weight armour is essential to protect soldiers and to allow them function efficiently. In both cases high velocity impacts occur and weight is crucial. Boron carbide has the potential to be an excellent material as it is very hard and very light; however it unexpectedly fragments under shock or high pressure loading. We have shown in preliminary work that by carefully adjusting the chemistry of the material with small additions of Silicon the mechanism of fragmentation under high pressure loading is suppressed, although it is unclear if this translates to improved impact performance.
Therefore in this work we aim to study in detail the mechanism by which boron carbide deforms and how this is altered by small additions of Silicon. This will involve deforming the materials within a high resolution electron microscope to understand which parts of the materials fail first and how. In parallel to these experiments, high velocity gas gun experiments on larger samples will help us understand how the deformation moves through the material, this is particularly important in impact resistant materials. Among other things this will require considerable improvements in our ceramic processing knowledge to produce the large amounts of the silicon stabilized boron carbide particularly for the gas gun experiments. However, if successful this knowledge will directly relevant to our industrial partners who will be able to quickly exploit it. The cutting edge analysis that will be required for this project will rely of devolvement of analytical techniques that can be applied in the future to a range of other materials. This includes high speed spectroscopic diagnostic tools which do not exist in the country at this time.

Demonstrating that by doping boron carbide with Si it is possible to create a low density ceramic with a hugoniot elastic limit above 40 GPa would have a large impact on a number of fields. It would open a range of aerospace applications including whipple shields for satellites and other vehicles. It would also be directly applicable for ballistic armour, where particularly for personal armour weight is crucial. The state of the art body armour systems worn by western soldiers weights around 12 kg and is a combination of ceramic plates and polymer fibres where the ceramic is the main component. There is a huge driver to reduce this by 50% along with other pieces of equipment, to reduce injury (simply from the weight) and improve effectiveness. This is added to obvious benefits that armour that resist high velocity impacts reduces the chances of serious injury or death, in peace keeping or combat situations.

Furthermore, the majority of personal armour (annual market value ~£5M) used in the United Kingdom is manufactured in the USA, for both economic and strategic reasons it would be advantageous for that manufacturing to be based here. This project has the potential to affect a step change in armour performance which could then be exploited by our project partners Kennametal Sintec. This would give the UK a competitive advantage allowing Kennametal to increase their market share and would also result in production being moved onshore which is strategically beneficial for the country. As in the past lack of production by other countries at times of need has resulting in supply shortages in the UK.

Finally the improvements in testing equipment and test methodologies either for small scale experiments or impact experiments will be available to the rest of the community either academic or industrial. It could be foreseen that for example the insitu TEM capabilities could be useful the cutting tool industry where hard brittle materials coming to contact with work pieces over small contact areas, generating very high stresses, and complex deformation patterns.