14 Dec 2021

Phase-Field Modeling of Nonequilibrium Solidification Processes in Additive Manufacturing

Abstract: This project models dendrite growth during nonequilibrium solidification of binary alloys using the phase-field method (PFM). Understanding the dendrite formation processes is important because the microstructural features directly influence mechanical properties of the produced parts. An improved understanding of dendrite formation may inform design protocols to achieve optimized process parameters for controlled microstructures and enhanced properties of materials. To this end, this work implements a phase-field model to simulate directional solidification of binary alloys. For applications involving strong nonequilibrium effects, a modified antitrapping current model is incorporated to help eject solute into the liquid phase based on experimentally calibrated, velocity-dependent partitioning coefficient. Investigated allow systems include SCN, Si-As, and Ni-Nb. The SCN alloy is chosen to verify the computational method, and the other two are selected for a parametric study due to their different diffusion properties. The modified antitrapping current model is compared with the classical model in terms of predicted dendrite profiles, tip undercooling, and tip velocity. Solidification parameters—the cooling rate and the strength of anisotropy—are studied to reveal their influences on dendrite growth. Computational results demonstrate effectiveness of the PFM and the modified antitrapping current model in simulating rapid solidification with strong nonequilibrium at the interface.

18 May 2020

PUBLICATION NOTICE: Phase-Field Simulations of Solidification in Support of Additive Manufacturing Processes

Abstract: For purposes relating to force protection through advancments in multiscale materials modeling, this report explores the use of the phase-field method for simulating microstructure solidification of metallic alloys. Specifically, its utility was examined with respect to a series of increasingly complex solidification problems, ranging from one dimensional, isothermal solidification of pure metals to two-dimensional, directional solidification of non-isothermal, binary alloys. Parametric studies involving variations in thermal gradient, pulling velocity, and anisotropy were also considered, and used to assess the conditions for which dendritic and/or columnar microstructures may be generated. In preparation, a systematic derivation of the relevant governing equations is provided along with the prescribed method of solution.