Numerical Analysis of Microstructure Development during Laser Welding Nickel-Based Single-Crystal Superalloy Part II: Multicomponent Dendrite Growth

Abstract

A thermal metallurgical coupling model was further developed for multicomponent dendrite growth of primary γ gamma phase during laser welding nickel-based single-crystal superalloys. It is indicated that welding configuration has a predominant role on the overall dendrite trunk spacing than heat input throughout the weld pool, and modifies the dendrite growth kinetics. The dendrite trunk spacing in (001) and [100] welding configuration is finer than that of in (001) and [110] welding configuration. In (001) and [100] welding configuration, the bimodal distribution of dendrite trunk spacing is symmetrical about weld pool centerline, the dendrite trunk spacing in [100] growth region near the weld pool center is coarser than [010], [0ī0] and [001] dendrite growth regions. In (001) and [110] welding configuration, the distribution of dendrite trunk spacing is crystallographically asymmetrical, and the dendrite trunk spacing in [100] growth region is severely coarser than that of [010] and [001] dendrite growth regions. (001) and [110] welding configuration is of particular interest, because dendrite trunk spacing decreases in [100] dendrite growth region and dendrite trunk spacing increases in [010] dendrite growth region from the maximum weld pool width to the end due to crystallography-dependent growth kinetics. Moreover, strict control of low heat input (low laser power and high welding speed) beneficially promotes fine dendrite trunk spacing and reduces the size of dendrite growth regions. High heat input (high laser power and low welding speed) monotonically coarsens dendrite trunk spacing. The dendrite trunk spacing is refined and [100] dendrite growth is suppressed by the optimum low heat input and (001) and [100] welding configuration to improve weldability. An alternative mechanism of solidification cracking because of asymmetrical dendrite trunk growth is proposed. The useful results facilitate understanding of single-crystal superalloys microstructure development and solidification cracking phenomena. The theoretical predictions agree well with the experiment results. Moreover, the model is also applicable to other single-crystal superalloys with similar metallurgical properties by feasible laser welding or laser cladding.