Numerical Analysis of Microstructure Development during Laser Welding Nickel-based Single-crystal Superalloy Part IV: Welding Conditions Optimization

The thermal-metallurgical modeling of columnar/equiaxed transition(CET), multicomponent dendrite growth and nonequilibrium solidification behavior was further developed during single-crystal superalloy weld pool solidification over a wide range of laser welding conditions (laser power, welding speed and welding configuration). It facilitates the unprecedent understanding of the effect of welding conditions on overall stray grain formation, dendrite trunk spacing and solidification temperature range throughout the weld pool. In order to eliminate the solidification cracking through microstructure control, it is imperative to optimize the welding conditions for successful defect-free laser welding. Crystallographic orientation of dendrite growth plays an important role than heat input in microstructure development and solidification cracking susceptibility. Optimum low heat inputs (low laser power and high welding speed) of solidification condition simultaneously prevent stray grain formation, refine dendrite size and mitigate the solidification temperature range to improve the weldability and weld integrity and vice versa. Nonequilibrium solidification behavior of the weld pool suppresses the solidification temperature range and dendrite size, and improves the solidification cracking resistance. The overall stray grain formation, dendrite trunk spacing and solidification temperature range in (001) and [100] welding configuration are beneficially reduced than that of in (001) and [110] welding configuration regardless of heat input. The theoretical predictions agree well with the experiment results. Moreover, this promising model is also available to other single-crystal superalloys with similar metallurgical properties during laser welding or laser cladding. (paper)