Microstructure control and hot cracking behavior of the new Ni-Co based superalloy prepared by electron beam smelting layered solidification technology

The prevention of hot cracking formation is of utmost importance in the production of the new Ni-Co based superalloys through the utilization of the electron beam smelting layered solidification technique (EBSL), as it ensures exceptional homogeneity and dependable consistency of the specimens. In contrast to previous studies that focused on minimizing the liquid film and solidification range, our methodology adopts a distinct approach. In this research, a novel methodology was employed to mitigate internal stresses through the implementation of equiaxed grain layers via an alternately reduced cooling method. This ultimately resulted in the elimination of hot cracking. To be more specific, the transition from a columnar to an equiaxed structure was observed during the layer-by-layer construction process in the fabrication of the new Ni-Co based superalloy in EBSL. The EBSL-Ni-Co superalloy, when subjected to the alternating reduction cooling method, exhibited an internal stress of 49 MPa. This value represents a significant reduction of 83.8% compared to the internal stress observed when employing the linear reduction cooling method. Additionally, the solvus temperature of the γ-γ` eutectic phases in EBSL-Ni-Co superalloys produced by the alternating reduction cooling method is significantly higher. Intriguingly, the Nth layer of the EBSL-Ni-Co based superalloys produced by EBSL simultaneously heats treated with the preceding layers. And the low melting point phase gradually dissolved back into the matrix. The implementation of an alternating reduced cooling method successfully mitigated the formation of the liquid film in the γ-γ` eutectic phase and the buildup of internal stresses in the EBSL-Ni-Co superalloy during its manufacturing process. These discoveries open up a novel preparation procedure pathway for the manufacture of crack-free superalloys with superior mechanical characteristics using EBSL.