Transparent glass–ceramics for ballistic protection: materials and challenges

The military ballistic protection market has reached approximately US$ 10 billion/year, and the civil market is also very significant and is steadily increasing, which drives research for new ballistic protection alternatives. Materials currently used and under development as transparent ballistic protection devices include glasses, glass–ceramics, single and polycrystalline ceramics, and polymer-composites. Glass–ceramics are a less expensive, versatile alternative to currently used transparent ceramics. Glass–ceramics are generally harder, stiffer, tougher, and stronger than glasses, and can be made transparent or opaque, according to the needs of the protective system. They can be easily shaped in simple or complex forms, are much less expensive than carbides and nitrades, and are less dense than transparent alumina or spinel. This positive combination of properties makes glass–ceramics suitable for a wide range of applications. However, for an effective development of new transparent glass–ceramics (TGC), it is vital to understand which key properties must be optimized. In this review, we compile information on the role of each material in multi-layer ballistic systems, give a brief description of ballistic impact, and the properties related to it, and discuss the development of TGC to be used as ballistic protection. Our aim is to describe the most important ballistic protection materials and to indicate the pathways that research on TGC for ballistic protection have taken. We finish by concluding that there are still several opportunities that warrant further research on this particular application of glass–ceramics.