Effect of directional solidification methods on the cast microstructure and grain orientation of blade shaped DZ125 superalloy

The cast structures of blade-shaped castings of DZ125 superalloy processed by liquid metal cooling (LMC) and high rate solidification (HRS) methods were studied to compare the benefits and drawbacks of these two methods. The morphologies and the growth direction of grains, primary dendrite arm spacing, γ' size were analyzed at different cross-sections along growth directions. The results indicate that the maximum deviation angle of primary dendrites from the sample axial decreases as the withdrawal rate increases from 40 to 110 μm/s for the central zone of HRS castings. At the withdrawal rate of 70 μm/s, the grains in the central zone of LMC casting have larger deviated angles, but the overall orientations of grains become more converging. The dendrites at the top of the blade are coarser than those at the middle, especially for the HRS castings. The γ' size becomes larger as castings solidify from the airfoil to the platform, but the difference of γ' size between the platform and the airfoil is smaller for LMC castings when the withdrawal rate is higher than 70 μm/s.