Single-pass ultra-high-power laser welding of thick nickel-based GH3535 superalloy: Microstructure evolution and microhardness

In comparison to narrow-gap laser welding, the ultra-high-power laser welding (UHPLW) represents an efficient method for single-pass welding of 22 mm thick GH3535 superalloy. This paper explored the microstructure evolution and microhardness distribution along the direction of weld penetration. The results showed that the direction of grain growth changed from horizontal to an inclined downward direction towards the bottom of the joint along the penetration direction. Precipitates distributed in the interdendritic region were identified as M2C and M6C carbides. The rapid cooling rate in the lower zone (LZ) of the joint resulted in slight elemental microsegregation and a lower volume fraction of precipitates than in other zones. The smaller grain size and the higher volume fraction of the precipitates resulted in a higher microhardness in the middle zone (MZ) of the entire joint. The study results will facilitate the application of UHPLW for the efficient welding of GH3535 thick plates.