Cutting costs across the defence sector can often be a difficult balancing act for manufacturing firms that need to ensure that a reduction in expenditure doesn’t translate to a compromise in quality. Dr Lars Schnetter tells Defence & Security Systems International how CeramTec-ETEC’s transparent ceramics.

How is CeramTec-ETEC placed within the defence sector?
Dr Lars Schnetter: We’re a well-known producer of alumina and silicon-carbide-based opaque armour ceramics, which can be found in most German military vehicles with composite armour, as well as many of those built by other European countries and the US. With over 20 years of delivering in this area, we’ve proven to be a reliable partner to the industry.

How do the properties of the different materials used for transparent armour applications compare?
If you look at different hard materials that can be used for transparent armour applications, you can find single crystals, glass and ceramics. Sapphire as a single crystal has a strictly oriented lattice structure with high atomic and ionic binding forces that lead to high hardness, strength and melting temperature. One of its disadvantages, though, is its optical and mechanical anisotropic behaviour. On the microscopic scale, glass is the complete opposite to a single crystal, with a more randomly oriented structure and weaker binding forces between its elements. This leads to lower melting temperatures and hardness. Simplified, it’s a frozen liquid.
For us, Perlucor – a polycrystalline ceramic material – can combine the positive aspects of both materials. It not only has a high bonding force comparable to sapphire between its atomic elements, with similar high hardness, strength and melting temperature, but it’s also optically and mechanically isotropic like glass, which has certain ballistic and processing advantages.

How does Perlucor compare with sapphire on a cost:performance ratio?
One of the advantages over sapphire on the technical side is related to the isotropic structure. If you do ballistic tests, you can observe a performance advantage of up to 20% or more. One of the assumptions is that the oriented sliding planes, which are typical for single crystals, appear to be the ‘weakest link’ and cause a failure prior to that of the transparent ceramics. In general, single crystals have different material properties depending upon their room orientation – behaviour that Perlucor doesn’t show. Another advantage is that Perlucor is much easier to grind and polish than sapphire, again related to the crystal structure and its mechanical isotropy, while contributing significantly to a lower cost. Furthermore, because of such a highly automated and fully optimised process, Perlucor has a cost:performance ratio much lower than other potential ceramic solutions.

What was the intention behind developing transparent ceramics?
Our goal is to commercialise transparent ceramics for a next-generation armour system from a reliable and cost-effective source. By first moving from armoured steel to an opaque ceramic composite solution, it was possible to achieve a weight saving of 50% or more; such differences can be even greater if you look into the opportunities of weight savings between existing glass transparent armour systems and possible new transparent ceramic composite systems.
Furthermore, the requirements concerning the multi-hit capability for transparent systems are also lower in comparison with the opaque field. The history of transparent ceramics suggests it hadn’t been much of a success story, which we believed to be down to the high costs associated with it. With that in mind, we started to develop a completely new process route to minimise costs significantly.

What are the main advantages of using transparent ceramics in armour systems?
If you think about building up a multilayer, ballistic window with a layer of transparent ceramics in front, Perlucor enables you to save up to 50% or more in weight. By using 6-11mm, depending on the threat level, you can save up to 50mm of glass. By using these advantages, you can build up a ballistic window for STANAG 4569 Level 4 threats at a reasonable thickness and weight.
Also, the multi-tile panel design offers an efficient transparent multi-hit solution. In the opaque field, the general trend for ceramics moves to smaller and smaller elements to adapt to the small distances between the shots as required, for instance within the STANAG 4569 specification. When a bullet hits one ceramic piece, just a small area of the whole armour is destroyed and a second shot can be stopped, even if it hits the armour close to the first shot. Within the transparent armour field you were very limited to fulfil these requirements, until today. The only way to go for a very efficient multi-hit solution, comparable to the opaque field, was to increase the thickness and therefore the weight significantly. Now, by having the possibility to transfer the proven technology of the opaque to the transparent field, you can use smaller Perlucor tiles and arrange them in a window to gain a multi-hit efficiency comparable to the opaque field.

What other applications could Perculor be used for?
It also acts as a very effective protective front layer for windows and optic equipment, such as infrared sensors, night-vision equipment and rifle telescopes, which would be of special interest with regard to equipment exposed to sand and dust in desert operations, such as Afghanistan or parts of Africa. Because of its very high chemical and heat resistance, Perlucor can be used in many other applications where glass-based materials do not offer satisfactory solutions, and we’ve already supplied various commercial products such as camera protection lenses, diving computer windows and others.

What other investments have been made recently, and what can we expect to see in the future?
Thanks primarily to the multimillion-euro investments made, we’ve been able to complete our latest developments as well as our factory, setting up everything for mass production along the way. The entire manufacturing process is now optimised to produce the perfect product quality at minimal cost. Using a highly automated and controlled process, we’re now able to deliver several thousand square metres of transparent ceramics at a time.
We’re aiming to perfect the optics within the multi-tile panel by refining the glue system. We’re also exploring combinations of thin ceramic layers attached to optics to maximise scratch and crack resistance, though, as it stands, only diamonds and rubies can scratch Perlucor. This is something which still has to be worked on, but it opens up a whole range of new application opportunities. We’re continually finding new ways to optimise our processes and improve our manufacturing technology. Combining the excellent physical and chemical properties with the much lower costs compared with other existing similar materials like sapphire, we believe that Perlucor could offer huge advantages when used for cost-effective solutions in stringent conditions for the foreseeable future.