Effect of Zr on microstructure and hot cracking susceptibility of ZGH451 superalloy fabricated by direct energy deposition

Abstract

Four groups of newly developed Ni-based superalloy samples with different Zr contents were manufactured by Direct energy deposition (DED). This study focuses on the influence of Zr element concentration on microstructure and cracking formation mechanism in DED-processed Ni-based superalloy ZGH451. Although Zr content is low, it strongly affects the formation of the precipitated phase and hot tearing tendency. Measurement of the crack area showed that the crack density value increases with the Zr concentration. According to thermodynamic simulation results and microstructures observed, Zr microsegregation in the interdendritic regions and considerable amounts of Zr is present in oxides or carbides. Zr contributes to forming large-size carbides mainly due to zirconia providing nucleation sites and the dissolution of Zr. Simultaneously, the solidification has been retarded due to the continuous accumulation of large Zr atoms, which increases the γ-γ′ eutectic fraction. Moreover, Zr addition could effectively decrease the solidus temperature of ZGH451 alloys, leading to the critical liquid film at the end of solidification. Based on these results, staying below 0.05 wt% of Zr content to reduce the risk of hot tearing in additive manufacturing superalloy was proposed.