# On the primary spacing and microsegregation of cellular dendrites in laser deposited Ni-Nb alloys

## TL;DR

This paper uses a phase-field model to study how laser parameters affect microstructure and Nb segregation in Ni-Nb alloys during additive manufacturing, revealing limitations of current models under rapid solidification conditions.

## Contribution

It introduces a phase-field simulation approach combined with finite element heat transfer to analyze microstructure and segregation in laser deposited Ni-Nb alloys, highlighting model limitations.

## Key findings

- Simulated primary spacings match power law and geometrical models.
- Non-equilibrium interface partitioning exceeds model capabilities.
- Laser parameters significantly influence microstructure and segregation.

## Abstract

In this study, an alloy phase-field model is used to simulate solidification microstructures at different locations within a solidified molten pool. The temperature gradient $G$ and the solidification velocity $V$ are obtained from a macroscopic heat transfer finite element simulation and provided as input to the phase-field model. The effects of laser beam speed and the location within the melt pool on the primary arm spacing and on the extent of Nb partitioning at the cell tips are investigated. Simulated steady-state primary spacings are compared with power law and geometrical models. Cell tip compositions are compared to a dendrite growth model. The extent of non-equilibrium interface partitioning of the phase-field model is investigated. Although the phase-field model has an anti-trapping solute flux term meant to maintain local interface equilibrium, we have found that during simulations it was insufficient at maintaining equilibrium. This is due to the fact that the additive manufacturing solidification conditions fall well outside the allowed limits of this flux term.