Advanced spinel and sub-μm Al2O3 for transparent armour applications |
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| Authors: | Andreas Krell Jens Klimke Thomas Hutzler |
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| Affiliation: | 1. Jiangsu Key Laboratories of Advanced Laser Materials and Devices, School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116, China;2. Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China;1. CEITEC—Central European Institute of Technology, Brno University of Technology, Technicka 10, 616 00 Brno, Czech Republic;2. Oxide Ceramics, Fraunhofer Institute of Ceramic Technologies and Systems, Winterbergstrasse 28, 01277 Dresden, Germany;3. Department of Materials and Environmental Chemistry, Stockholm University, Svante Arrhenius vag 16C, 106 91 Stockholm, Sweden;1. Engineering Ceramics Department, Korea Institute of Materials Science, 797 Changwondaero, Changwon, Gyeongnam 641-831, Republic of Korea;2. Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry of Education Key Laboratory for Green Preparation and Application of Functional Materials, School of Material Science and Engineering, Hubei University, 368 Youyi Avenue, Wuhan, Hubei 430062, China;1. Engineering Ceramics Department, Korea Institute of Material Science, 797 Changwondaero, Changwon, Gyeongnam 51508, Republic of Korea;2. School of Advanced Materials Science and Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk 39177, Republic of Korea |
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| Abstract: | Hardness is important for a high ballistic strength, and with HV10 = 20–22 GPa sintered sub-μm Al2O3 is the hardest of all transparent materials for compact windows. However, light transmission through polycrystalline Al2O3 is limited by birefringent scattering losses: high transmissions are known at larger IR wavelengths for grain sizes of about 0.5 μm but the visible real in-line transmission RIT is only 70–75% of the theoretical maximum at 0.8–1 mm thickness. These losses will be the higher for thicker components whereas a safe ballistic performance requires 1.5–2 mm thickness at least. New technologies bring the transmission closer to the limit associating grain sizes of 0.3 μm with an RIT of 84–93% of the theoretical maximum (thickness 0.8 mm). However, even these extreme results give again rise to doubt that it will ever be possible to manufacture larger and thicker Al2O3 windows with a sufficiently high transparency.On the other hand, new results are presented for fine-grained spinel with RIT close to the theoretical maximum and with a hardness that approaches sapphire. In first ballistic tests this spinel outperformed sapphire of different orientations. It is, therefore, suggested that sub-μm Al2O3 may be a good choice for IR windows or as armour for low threat applications where thinner tiles can be used. Most threats, however, require thicker windows where the new spinel appears as one of the most favourable candidates. |
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