Numerical Analysis of Microstructure Development during Laser Welding Nickel-based Single-crystal Superalloy Part V: Crystallography-dependent Aluminum Redistribution

Abstract

Abstract The thermal-metallurgical modeling of alloying aluminum redistribution was further developed through couple of heat transfer model, dendrite selection model, multicomponent dendrite growth model and nonequilibrium solidification model during three-dimensional nickel-based single-crystal superalloy weld pool solidification over a wide range of welding conditions (laser power, welding speed and welding configuration). It is clearly indicated that welding configuration plays more important role than heat input in aluminum redistribution. The bimodal distribution of aluminum concentration along the solid/liquid interface is crystallographically symmetrical about the weld pool centerline for (001) and [100] welding configuration, while the distribution is crystallographically asymmetrical about the weld pool centerline for (001) and [110] welding configuration. Optimum low heat input (low laser power and high welding speed) with (001) and [100] welding configuration beneficially suppresses the aluminum concentration, reduces the vulnerable [100] dendrite growth region to minimize the solidification cracking susceptibility and improve weldability and vice versa. The overall aluminum concentration on the left side of the weld pool is beneficially smaller than that of right side in (001) and [110] welding configuration throughout the weld pool due to crystallographic orientation of dendrite growth regardless of the heat input. The mechanism of asymmetrical solidification cracking because of crystallography-dependent alloying solute inhomogeneity was proposed. The welding conditions, weld pool geometry, solidification conditions, dendrite selection, alloying redistribution and solidification cracking susceptibility are closely correlated. The theoretical predictions agree well with the experiment results. Moreover, the promising results facilitate the understanding of solidification cracking phenomena, and the useful model is also applicable to other single-crystal superalloys with similar metallurgical properties for successful defect-free laser welding or laser cladding.