The Effects of Melt Pool Geometry and Scan Strategy on Microstructure Development During Additive Manufacturing

Abstract

During the powder bed fusion additive manufacturing (AM) process, hundreds of grains may solidify simultaneously within the melt pool, depending upon the processing conditions and the grain size of the base plate and powder. Thus, a small variation in the shape of the melt pool or scan strategy may result in very different as-printed microstructures, since new grains may become more favourably aligned with the overall direction of growth. The microstructure affects the performance of the additively built component, and it is therefore critical to understand the interplay between the initial microstructure, material properties, heat source, and scan strategy on determining the as-printed microstructure. We examine columnar grain growth during AM using a phase-field model to perform simulations with single melt pools predicted by the cylindrically symmetric Rosenthal solution. Quantitative measures of the competitive grain growth are extracted from the simulation data. To aid in their understanding, we map these quantities onto visualizations of the microstructure and compare them to the inverse pole figure map, from which we find that the crystallographic directions of the grains that grow closest to the centre of the laser track may not be preferentially aligned with the scan direction.