Numerical Analysis of Microstructure Development during Laser Welding Nickel-based Single-crystal Superalloy Part III: Nonequilibrium Solidification Behavior

Abstract The thermal-metallurgical modeling of primary γ gamma phase nonequilibrium solidification behavior during laser welding nickel-based single-crystal superalloy is further developed through coupling of heat transfer model, multicomponent dendrite growth model and nonequilibrium solidification model to evaluate solidification cracking susceptibility and advance the understanding of the material weldability. The useful relationship among welding conditions (laser power, welding speed and welding configuration), weld pool geometry, dendrite selection, dendrite growth, solidification temperature range, solidification cracking susceptibility and weldability are established for welding conditions optimization and microstructure control. It is indicated that for (001) and [100] welding configuration, solidification cracking susceptibility along the solid/liquid interface is symmetrically distributed about the weld pool centerline. It is crystallographically favorable for mitigation of solidification cracking with bimodal distribution of solidification temperature range. By contrast, for (001) and [110] welding configuration, solidification cracking susceptibility is asymmetrically distributed. The solidification cracking susceptibility of the unfavorable [100] dendrite growth region on the right side of the weld pool is higher than that of [010] dendrite growth region on the left side due to the enlargement of solidification temperature range. The mechanism of asymmetrical crystallography-dependent solidification cracking is proposed. Asymmetrical dendrite growth region induces asymmetrical solidification behavior and solidification cracking susceptibility along the solid/liquid interface, although heat transfer is symmetrical. The overall solidification temperature range of (001) and [100] welding configuration is beneficially narrower than that of (001) and [110] welding configuration throughout the weld pool regardless of heat input. The theoretical predictions agree well with the experiment results. In addition, the promising model is also applicable to other single-crystal superalloys with similar metallurgical properties during laser welding or laser cladding.