Nanograin Ceramic Optical Composite Window

A high-strength low-cost alternative to single-crystal sapphire is required to meet the increased performance demands of the Navy's next-generation E/O applications. Technology Assessment & Transfer is the leading supplier of polycrystalline transparent spinel ceramics. Spinel, with a hardness that is slightly lower than that of sapphire and a lower strength (350 MPa vs. 750 MPa), has the benefits of being cubic, polycrystalline, and possessing a slight increase in transmission over sapphire in the MWIR. Although the monolithic values of strength are lower than that of sapphire, in opaque systems such as alumina, toughness, strength, and hardness were found to nearly triple over the single phase values with additions of SiC. Similar gains in strength values for spinel can be realized through the successful fabrication of a transparent nanocomposite and would equal if not eclipse that of sapphire. Using the well researched systems containing phases of alumina, silicon carbide, and zirconia, nanocomposites will be fabricated to achieve peak transparency in the MWIR. After characterizing the mechanisms and microstructure for the initial material, process refinements will attempt to achieve visible transparency in the Phase I option and Phase II efforts.