Effect of Dendrite Refinement on Microstructure and Stress Rupture Properties of Third-Generation Nickel-Based Single-Crystal Superalloys

Abstract:

A third-generation single-crystal superalloy WZ30 was used to prepare single-crystal samples with varying dendrite spacings under different processing techniques. The microstructure and stress rupture properties were studied and compared. The results show that, by improving the thermal-insulation effect between heating zone and cooling zone of the directional solidification furnace, the average primary dendrite spacing of the as-cast sample is reduced from 415 μm to 251 μm, leading to a noticeable refinement of dendrite and eutectic structure. At the same time, dendrite refinement can simultaneously decrease the volume ratio of casting porosity from 2.29% to 0.21%. Additionally, the γ′ phase in both the dendritic and inter-dendritic regions undergoes refinement, with a more uniform size distribution and a more regular shape. After the subsequent solid solution and aging treatments, the smaller γ′ precipitates with higher cubic degree are obtained in samples after dendrite refinement, whose service life at 980 °C/ 280 MPa is improved by 13.8%.