Weldability Improvement of Additively Manufactured Nickel-Based Superalloy by Controlling W and Si Migration at Solidification Front

Nickel-based superalloy components prepared by laser powder bed fusion (LPBF) are increasingly being used in the hot ends of aeroengines, which still need to be laser-welded to realize the assembly connection of large closed structures. However, the unique microstructural characteristics of LPBFed parts render them more poorly weldable than casts and wroughts, especially in cracking-sensitive superalloys. In this study, cracking mechanisms were analyzed by performing laser deep fusion welding on an LPBFed Haynes 230 alloy. The key factors leading to weld cracking were strongly correlated with the low-melting-point TCP phases enriched with W, Si, Al, and silicides, both of which tended to be distributed in the boron(B)-rich region and exhibited poor coherence with the matrix. In addition, the flow behavior of the molten pool affected the solidification rate of the weld, resulting in large solidification shrinkage stresses in the cracking-sensitive zone (CZ) part of the weld. In order to minimize the development conditions of the cracking-sensitive phases, reducing the content of W (from 14.96 to 13.56 wt.%) and Si (from 0.47 to 0.25 wt.%) was chosen to alleviate the segregation of W, Si and C elements in the solid phase at the end of solidification. Thus, TCP phase and silicides were transformed into carbides, which successfully suppressed weld cracking, reducing the crack depth ratio from 0.70 ± 0.08 to zero. New insights into the weldability improvement and crack inhibition mechanism of laser-welded additively manufactured cracking-sensitive superalloys are provided, accelerating the rapid application of large assemblies.