The development of grain structure during additive manufacturing

Abstract

Additive manufacturing of structural alloys results in the formation of complex microstructures, often with long, columnar grains that grow epitaxially from existing grains. A phase-field modeling framework is presented that considers solidification along a single track of 316L stainless steel in a regime where the solid-liquid interface is moving sufficiently fast that there is absolute interfacial stability with negligible composition variations. By coupling to a thermal field of a moving laser source, the model captures the trajectory of grains solidifying around a melt pool. The effect of interfacial kinetic anisotropy on the predicted as-solidified microstructures is examined through three-dimensional simulations. Through a combination of qualitative and quantitative analyses, we find that kinetic anisotropy has the largest impact along the center of the laser track and that the grain morphology in the early stages of solidification is predominantly due to the shape of the melt pool.