DEVELOPMENT AND EVALUATION OF TRANSPARENT ALUMINUM OXIDE
Final rept. 1 Jun 1966-30 Jun 1967
AVCO MISSILES SPACE AND ELECTRONICS GROUP LOWELL MA AVCO SPACE SYSTEMS DIV
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Polycrystalline alumina Al2O3 possessing high total and in-line transmission in the visible range was prepared successfully by a combined high temperature hot forging and annealing operation. Transparency was found to be produced by a combination of several pore removal mechanisms active during deformation and primary recrystallization. A strong basal texture normal to the pressing direction was found for both deformation and recrystallization structures, and the high in-line transmission characteristics were thought to be due to a lowering of birefringent scattering because of this texture. Initial experiments were conducted to define the critical strain for recrystallization, and to date it is thought that this strain lies between 4 and 10 percent. Room and elevated temperature bend strengths of these materials were equivalent to opaque but dense pressure or pressureless sintered alumina having a comparable grain size.
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