MICROSTRUCTURE STUDIES OF POLYCRYSTALLINE REFACTORY OXIDES
Summary rept., 25 Mar 1966-24 Apr 1967
AVCO MISSILES SPACE AND ELECTRONICS GROUP LOWELL MA AVCO SPACE SYSTEMS DIV
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Hot working polycrystalline alumina, utilizing a press forging technique, was extensively investigated. Primary recrystallization followed the working and resulted in either single crystals strain-anneal technique or relatively fine-grained structures. The basal texture present after recrystallization was identical to the deformation texture this and the equiaxed recrystallized structures suggested that oriented nucleation was important. At larger grain sizes, an elongated grain structure was observed and was attributed to oriented growth. The marked basal texture suggested that basal slip was the predominant deformation mode the probability of other deformation mechanisms was also discussed. Addition of 14 MgO retarded recrystallization and a number of such samples, possessing a pronounced basal deformation texture, were used for mechanical properties determination. The working led to no less of structural integrity, and the strength was surprisingly constant with grain size, at least in the range 3.5-10.5 microns. The larger-grained worked samples were stronger than hot-pressed samples of equivalent porosity and grain size. The high ductility, up to 75 height reduction being achieved without much difficulty, suggested that hot working could be used to produce shaped bodies.
- Ceramics, Refractories and Glass