Insights into process optimization and induction preheating for crack-free laser metal deposition of nickel-based superalloy K417G

The additive manufacturing of high-γ′ precipitation-rate superalloys presents both benefits and challenges. For the fabrication of dense and crack-free K417G superalloy, this study utilized laser metal deposition (LMD) in conjunction with induction heating, conducting a comprehensive experimental exploration. The findings demonstrate that a medium energy density promotes densification. The microstructure of deposited K417G includes γ matrix, γ′ precipitation, MC carbides, and γ/γ′ eutectic. The cracking mechanism during the LMD process is intricately related to process parameters. Insufficient energy density leads to the formation of unmelted powder, resulting in localized oxidation and subsequent oxide-induced cracking. In other scenarios, it manifests as liquation cracking. Moreover, an increase in preheating temperature to between 700 °C and 900 °C induces additional ductility-dip cracking. However, by raising the preheating temperature to 1100 °C and maintaining a moderate energy density, crack-free deposits can be achieved. Such conditions not only mitigate thermal stress, but also minimize phase transition stress by preventing repeated γ′ dissolution and precipitation, resulting in a more homogeneous γ′ dimensions distribution. This study confirms the printability of K417G superalloy and enhances the technological understanding of using LMD in conjunction with induction heating to prepare non-weldable superalloys.