EFFECTS OF CREEP ON THE MICROSTRUCTURAL FEATURES OF AN OXIDE-DISPERSION-STRENGTHENED SUPERALLOY

The effects of high temperature creep on the microstructure and the grain boundaries of the oxide-dispersion-strengthened superalloy MA6000 are investigated by means of transmission electron microscopy. Rafting of the gamma' phase is observed in the elongated grains, whereas in the small nonrecrystallized grains gamma' rafting does not occur. Dislocations form networks around gamma' precipitates only in particular areas of the coarse grains where the oxide particles are absent. In the rest of the areas, where oxide dispersion is homogeneous, dislocations are pinned to the hard oxide particles instead of accumulating at gamma-gamma' interfaces. Dislocation networks around the gamma' phase are not observed in the small grains. There is no detectable influence of high temperature creep on the grain boundaries of the material. The majority of them are of the small angle type and exhibit a very disordered morphology. Large angle grain boundaries are randomly oriented and they are mainly decorated by chromium carbides.