Effect of Ru on macro-/micro-structure evolution within platform of Ni-based superalloy single crystal blades

Abstract The effect of Ru-addition on the macro-/micro-structure evolution within platform of Ni-based superalloy single crystal turbine blades was investigated in this study. CM247 LC was used as the baseline alloy, and two modified alloy contained 3 wt% and 5 wt% Ru, respectively, were prepared at the expense of Ni in the baseline alloy. The results showed that the dendrite patterns within platform regions were non-uniform under the blade cluster condition. Different dendrite growth patterns were observed within platform overhangs on heater side and shadow side for these alloys. When the shadow side was free from stray grains, the secondary dendrites laterally spread into the overhang region and blocked by higher order dendrite branches, due to a high local undercooling. On the heater side, secondary dendrite arms could extend into the overhang region and reached extremities with few disruptions of higher order dendrite. With the Ru-addition increasing, stray grain occurrence increased in the platform regions of the blades, particularly on the shadow side. The Ru-addition also led to changes in solidification characteristics. In the solidified samples containing 3 wt% Ru, cracks along stray grain boundary were found, which may be caused by deficient of intergranular solid bridges and liquid feeding.