Study on the Temperature Field and Grain Structure of Large-Scale DZ466 Ni-Based Superalloy During Directional Solidification Process

Large-scale DZ466 superalloy tube-like cast assemblies were designed to mimic the variable cross section and hollow structure of industry gas turbine (IGT) turbine blades. By combined computational simulation and unidirectional solidification experiments, the temperature fields, solidification process, and microstructure of the casts were studied. It is shown that the temperature gradient decreases with the increase of solidification distance, resulting in the widening of the mushy zone. The columnar grains grow along the <001> orientation with an angle lower than 12° after competitive and cannibal growth. The primary dendrite arm spacing (PDAS) of columnar crystals is influenced by the solidification distance, position, and the wall thickness. Typically, the PDAS at the upper part of the center side of the cast solidified with a withdrawing rate of 6 mm/min is increased from 330 μm to 380 μm when the wall thickness varied from 3 mm to 7 mm. The γ′ phase in dendrite trunks is finer and more homogeneous than that in the interdendritic region. After heat treatment, large blocks of γ′ phase emerged in the interdendritic region near the cooling disc.