Hot-Working of Aluminum Oxide: II, Optical Properties

Polycrystalline Al₂O₃ fabricated into plates or shapes by hot-working techniques exhibits high in-line transmittance from 0.4 to 5.5 μm. Examination of the product by an inverse pole figure technique demonstrated a strong {0001} texture normal to the pressing direction for both equiaxed and textured microstructures. The crystallographic texture was attributed to the dominance of basal slip in deformation. A comparison of transmissivity in the 2 principal directions of a forged plate strongly suggested that a reduction of birefringence resulting from the crystallographic texture was partially responsible for the high transmissivity. The absorption coefficient at 4.5 μm was 0.15 mm^-1, ∼ that for sintered Al₂O₃ and 5 times that for sapphire