Eq 3

Fig. 4 Reciprocal of the grain coarsening exponent (1/n) as a function of temperature for nanocrystalline materials. RT, room temperature. Source: Ref 14

Experimentally, a strong correlation exists between the closure of open porosity and the onset of exaggerated grain growth (Ref 17, 18, 19, 20, 21, 22, 23, 24, 25). As shown in Fig. 5 for nickel and TiO2, accelerated grain growth occurs at densities above about 90% when the pores become isolated or closed. Often, the final grain size upon full densification is close to 1 i'm. In contrast, grain growth is much less exaggerated at high densities for nonagglomerated A1203 powders (Ref 26). Abnormal grain growth, localized excessive growth of a few grains, has been observed in alumina-zirconia nanocomposites (Ref 27), silicon (Ref 28), and iron (Ref 10). It is illustrated for iron in Fig. 6.

70 75 00 85 90 95 100
0 0

Post a comment