HOT-WORKING OF ALUMINUM OXIDE. I. PRIMARY RECRYSTALLIZATION AND TEXTURE

Polycrystalline aluminum oxide was hot‐worked at 1750° to 1950°C and at stresses <21, 000 psi using a press‐forging technique. No ductility problems were encountered, and maximum true strains and strain rates of ‐1.25 and 0.2/min, respectively, were observed. Deformed samples often showed grain elongation in addition to a marked basal crystallographic texture, which suggested that basal slip was the predominant deformation mode. However, nonbasal slip, grain boundary sliding, and diffusional deformation were all thought to contribute to the ductility. Primary recrystallization occurred during or after the deformation and resulted in equiaxed microstructures, although the basal texture was retained. Because of a severe shear strain gradient during deformation, nonuniform microstructures were usually obtained, and this provided a means for growing single crystals by strain anneal. Although no conclusions can be drawn concerning the origin of the recrystallization texture, it is suggested that pores are preferential sites for recrystallization nuclei. MgO in solid solution (1/4%) retarded primary recrystallization. Copyright © 1969, Wiley Blackwell. All rights reserved