Simulation and analysis of ${\gamma}$-Ni cellular growth during laser powder deposition of Ni-based superalloys

TL;DR

This study uses 3D phase-field simulations combined with a thermal model to analyze cellular microstructures in Ni-based superalloys during laser powder deposition, revealing relationships between solidification conditions and microstructure features.

Contribution

It introduces a coupled simulation approach to analyze cellular growth in Ni-based superalloys during additive manufacturing, linking microstructure features with solidification parameters.

Findings

Cell spacings follow specific scaling laws with G and V.

Cell core compositions agree with dendrite growth theory.

Identified a bridging plane where primary γ phase coalesces.

Abstract

Cellular or dendritic microstructures that result as a function of additive manufacturing solidification conditions in a Ni-based melt pool are simulated in the present work using three-dimensional phase-field simulations. A macroscopic thermal model is used to obtain the temperature gradient $G$ and the solidification velocity $V$ which are provided as inputs to the phase-field model. We extract the cell spacings, cell core compositions, and cell tip as well as mushy zone temperatures from the simulated microstructures as a function of $V$. Cell spacings are compared with different scaling laws that correlate to the solidification conditions and approximated by $G^{-m}V^{-n}$. Cell core compositions are compared with the analytical solutions of a dendrite growth theory and found to be in good agreement. Through analysis of the mushy zone, we extract a characteristic bridging plane, where the primary $\gamma$ phase coalesces across the intercellular liquid channels at a $\gamma$ fraction between 0.6 and 0.7. The temperature and the $\gamma$ fraction in this plane are found to decrease with increasing $V$. The simulated microstructural features are significant as they can be used as inputs for the simulation of subsequent heat treatment processes.