Low-Cost IR Windows and Lenses made from Polycrystalline YAG

This Small Business Innovation Research (SBIR) Phase I proposal from Materials and Systems Research, Inc. (MSRI) and University of Utah (subcontractor) seeks to fabricate single-phase, polycrystalline yttrium aluminum garnet (YAG) with a density greater than 99.95% and a mean grain size less than 1 micron. Polycrystalline YAG with these properties will have optical transmittance comparable to that of single crystal YAG in the midwave (3-5 micron) and long wave (8-14 micron) infrared windows. The high density and small grain size will be achieved by a fabrication route that will combine the following steps: preparation of a stable suspension of submicron YAG powder, forming a green compact by colloidal isopressing, and a two-stage densification by pressureless sintering followed by hot-isostatic pressing. The proposed fabrication route has two distinct advantages over conventional powder processing methods: (a) it eliminates microstructural inhomogenities that limit strength, durability and optical transmittance in conventional powder processing, (b) it eliminates a number of steps involved in conventional processing and leads to a lower cost. Research in Phase I will fabricate disks 100-150 mm in diameter and 3-6 mm in thickness. Measurements of fracture strengths, fracture toughness, and optical transmittance will be done by University of Utah under a subcontract.