A Physics-based investigation of solidification morphology and microcracking in a high-y Ni-based superalloy during Selective Laser Melting

This work employs a computational approach to investigate how local thermal conditions and dendritic growth angles influence the solidification morphology of the difficult-to-print Ni-based superalloy CM247LC during Selective Laser Melting (SLM). A conduction-based thermal model incorporating temperature-dependent material properties was used to extract local thermal gradients and cooling rates under single-track laser conditions. These thermal histories were then used as input to a multicomponent phase-field model to simulate the evolution of the solidification front, including nanovoid formation and elemental segregation. This framework enables the simulation of location-specific solidification morphologies and microsegregation under SLM conditions.

Model predictions were validated through comparison with SEM and optical microscopy, revealing a direct correlation between dendrite development, nanovoid size distribution, and microcracking propensity. Based on these results, a microcracking mechanism is proposed in which nanovoids form within interdendritic regions during solidification and subsequently coalesce to form microcracks. Once calibrated against thermodynamic data, the phase-field model was used to examine how processing parameters govern the transition between cellular and dendritic growth. The results demonstrate that reducing lack-of-fusion porosity requires a transition to dendritic solidification, which in turn promotes microcracking in CM247LC. These findings indicate that the fabrication of crack-free and porosity-free components requires a processing window that achieves sufficient melting while maintaining cooling rates that favour a cellular microstructure.