Evolution of Temperature, Microstructure and Inter-Granular Stresses During Directionally Solidification Process of a Ni-Based Superalloy

In order to gain a better understanding of the detrimental effects of grain boundaries on the creep and fatigue life of a nickel based directionally solidified super alloys, the effect of the grain mis-orientation and temperature changes on the internal stresses were investigated. The changes of cooling rate, nuclei count and stress level and components in different parts of the casting were considered during solidification process in a Bridgeman furnace. During solidification, constriction of grain growth in one direction, which is due to the heat transfer direction, eliminates grains with large mis-orientations. The remaining grains are close to [001] direction. Temperature profile of the modeled carrot samples demonstrated a significant variation in the cooling rate along the axis of the sample. The mis-orientation of the grains was also characterized. Stress components and effective stress were calculated and it was shown that the effective stress is lower than the yield stress of the alloy.