New Ceramic Armor Materials — From Boron Suboxide to Diamond
At the present time, the only commonly-encountered ceramic armor materials are alumina, boron carbide, and silicon carbide. All of these materials were introduced in the 1960s and saw service in Vietnam-era armor plates. They haven’t changed since. The current state of the art — the monolithic, multi-curved boron carbide armor ceramic tile — was developed by scientists at the US Army Natick Research and Development Laboratories and Picatinny Arsenal in 1965. If there has been any innovation in the many years since, it has been to manufacturing processes; these innovations have brought boron carbide tile production costs down and have facilitated high-volume production, but, pointedly, they have not improved performance. (And, indeed, in many cases these innovations have actually reduced performance — e.g. in reaction-bonded boron carbide — RBB4C — that is softer, denser, and ultimately just less protective than the 1965 product.)
All three of these old ceramic armor materials have their shortcomings: Alumina is far too heavy, to such an extent that even steel armor is now giving it a run for its money; silicon carbide is, although much lighter, still heavy enough to be burdensome; the best grades of boron carbide, although nearly 40% lighter than alumina and more than 20% lighter than silicon carbide, are rather expensive and underperform against bullets with cemented carbide (WC-Co) cores.
Yet by no means are these three ceramic materials the only ones suitable for armor applications. As I’ve mentioned in older posts, many other ceramic materials have been successfully tested towards armor applications, and there is an ongoing search, at Diamond Age and elsewhere, for a better ceramic armor material — something which out-performs boron carbide on a weight-basis, and maintains this high level of performance against extra-potent threats such as WC-Co-cored rounds.
To that end, one material which has captured the DoD’s imagination of late is boron suboxide, B6O. It mirrors boron carbide in its low density (2.52 gm/cc) and its extremely high hardness (>3000 HV1) and current thinking is that it should perform well against even the toughest threats — unlike boron carbide, which, as mentioned previously, can be less than perfectly reliable. The trouble with B6O is that it’s even harder to process and sinter than boron carbide, already a very difficult material to work with. Even worse, B6O is staggeringly expensive to synthesize as a raw material. For these reasons, its commercial development has never gotten off the ground — and boron suboxide armor may never enter mass production.
The aluminum dodecaboride AlB12 and the aluminium-magnesium-boron compound AlMgB14 are also attractive materials — both as standalone pure ceramic phases for armor plate development, and as candidates for better cermet development. AlB12 and AlMgB14 are very similar to each other, and to boron carbide: Their density is very low at roughly 2.5 gm/cc, they are all of similar hardness, and, unless something like the Lanxide process is employed, they’re best densified with the application of moderate pressure, e.g. in a hot-press or SPS/FAST furnace. AlB12 and AlMgB14 have never been tested against WC-Co cored projectiles, but have shown good efficacy against steel-cored threats. The Achilles heel of these ceramic materials is the fact that they’re very expensive to synthesize from the commercially-available materials that are the product of boron mining. (Boron carbide, in contrast, is relatively easy to produce from cheap raw materials such as boric acid.)
Another option, mentioned in a few scientific papers over a decade ago, is a composite material made from roughly 60% boron carbide and 40% calcium hexaboride (CaB6). This multiphase ceramic material has some inherent ductility, is slightly lighter than boron carbide, is slightly easier to densify, and appears to outperform pure boron carbide in head-to-head ballistic tests. CaB6, however, is not stable in the presence of water — and degrades severely even upon exposure to moderately humid air — which is a trait that may limit its use in armor systems where, by definition, stability and reliability are of key importance. Diamond Age has worked with CaB6-B4C composites that, quite literally, turned to dust following several months of exposure to ambient conditions. These test tiles started exhibited spalling corrosion within days of their densification, which is certainly an extremely undesirable trait in an armor material. Coatings which prevent the decomposition of CaB6 may, however, eventually enable the utilization of B4C-CaB6 composite plates… but not without some degree of legal liability and reputational risk.
Yet as this CaB6-B4C composite makes apparent, one doesn’t need to replace boron carbide entirely — strengthening it with a dopant or secondary phase is also a viable strategy, and a very promising one. At Diamond Age, we’ve gotten very impressive results with B4C-TiN composites, which have a slightly higher density than pure boron carbide, but which display enhanced fracture toughness and better ballistic performance. The addition of very small amounts of silicon or aluminum dopants to boron carbide, or tailoring the material’s stoichiometry so that it’s more boron-rich than usual (> B6.5C), have also been proposed as methods for producing a boron carbide ceramic product that’s more resistant to failure via shear amorphization, and would thus exhibit more predictable performance against WC-Co-cored ballistic threats.
An entirely different approach, which is perhaps the most promising approach, lies with high-pressure chemistry and engineering, for these enable the production of metastable high-pressure bulk materials, thereby opening up new frontiers in armor material development. Diamond Age has been experimenting with HPHT polycrystalline diamond ceramics for some years and has recently been issued a patent on the technology. Bulk diamond is much harder, much tougher, and much better-performing than any known ceramic material. We’re now at a stage where we’re beginning to make large diamond tiles on a large enough scale for commercialization, and we’re actively working on R&D, so that even larger, stronger, and superlatively high-performance diamond tiles are available for next-generation armor applications. For instance, by utilizing fullerenes as a starting material, instead of carbon black, it seems possible to make bulk diamond tiles that are structured, comprised of aggregated diamond nanorods, and which are so hard and tough that they may be the truly ideal and ultimate armor material — unsurpassable.
Plates made with our current diamond tiles are already capable of stopping threats such as the M855 at as little as 2.2 pounds per 10×12″ shooter’s cut plate. In the very near future, we believe that diamond-faced armor plates should be able to stop the APM2 at well under 4 pounds per body armor plate.
For more information on our diamond armor plates, please click here.