Edge Defined Film-fed Growth (EFGTM) sapphire crystals are being grown commercially as large, thick sheets that measure greater than 305 mm wide, 775 mm long, and 11 mm thick. The high strength, high hardness, and good transparency in the visible and infrared spectra make sapphire an ideal choice for transparent armor applications. This paper will discuss the properties of large sapphire sheets and the results from ballistic testing of selected sapphire transparent armor panels.
High strength edge bonds have been achieved between individual sapphire components, showing promise for fabricating window blanks up to 600 mm diameter or larger in size. Several bonding methods were investigated, with a directed-energy diffusion-bonding method yielding components with bond fracture strengths of 200 MPa (30,000 psi). Bonded sapphire components 600 mm long and 3 mm thick with a 75 mm wide bond line have been produced. When polished, the bonded windows show no degradation in transmittance or transmitted wavefront quality. Process scale up to larger bonds lines is planned. Mechanical and optical characterizations of sub-scale edge-bonded sapphire windows are presented.
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