Dislocation Motion and Crack Propagation Effects in the Iron Oxide - MgO System

摘要

The method of indentation hardness to introduce and move fresh dislocations is applied in a concentration gradient. Using this technique, much information can be obtained with a few samples. The crack propagation and hardening effect of a divalent and trivalent iron concentration gradient were studied in magnesium oxide single crystals. The relative hardening versus iron concentration was found to be a nonlinear relation. An explanation is presented based on equilibrium constant relationships to account for this power variation. Samples containing Fe(+3) ions in solid solution were aged for various times to study the effects of magnesioferrite precipitation in the concenetration gradient. Once coherency was broken, the hardening of MgO due to the magnesioferrite precipitates was found to be a linear function of the iron concentration. A mechanism to explain the change in crack propagation direction upon reaching a critical trivalent iron concentration is also presented. (Author)