Critical factors in the templated grain growth of textured reaction-bonded alumina

The Templated Grain Growth (TGG) of Al2O3 occurs in three stages: densification, radial growth of individual template grains until template impingement, and template grain thickening. Significant template growth occurs only after densification to similar to 90% density. Template Loading determines the intertemplate spacing and, subsequently, the degree of growth. The spacing distance can be predicted from the initial template concentration and template dimensions, Thermodynamic conditions favorable for template growth occur when the size ratio between the template thickness and matrix grains is greater than or equal to 1.5. The initial template concentration should be less than a critical template concentration, V-T,V-C, to achieve textured ceramics with a narrow orientation distribution. For this system, which uses 20 +/- 5 mu m x 2 mu m template particles and uniaxial pressing as a forming technique, V-T,V-C is between 5 and 10 vol%.