Hot‐Working of Aluminum Oxide: II, Optical Properties

Polycrystalline Al 2 O 3 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 Al 2 O 3 and 5 times that for sapphire