Microstructural study of a mechanically alloyed ODS superalloy

Extruded bars of oxide-dispersion-strengthened (ODS) alloy MA-6000 have been annealed isothermally as well as in temperature gradients. The temperatures used for annealing produced secondary recrystallization in all the samples, although the final grain aspect ratio was different for each annealing process. Interrupted gradient anneal experiments showed a curved secondary recrystallization front, with the surface recrystallizing at a lower temperature than the interior. It is believed this is caused indirectly by the strain gradients arising during extrusion. Grain-orientation analysis of recrystallized material revealed that a <110> fiber texture is present. A progressive grain reorientation toward <110> has been measured behind the recrystallization front using microbeam electron diffraction. In addition, changes in the distribution, size, and morphology of different types of precipitates and particles occurring during various stages of annealing have also been studied. Grain-boundary pinning by the stable oxide particles plays an important role in determining the grain growth behavior at high temperatures.