Understanding Phase Transformations During Additive Manufacturing Toward the Design of Functionally Graded Materials

Functionally graded materials (FGMs), with spatially varying composition, can be fabricated using laser based directed energy deposition (DED) additive manufacturing (AM) with powder feedstock, where the ratios of powder flowed into the melt pool are varied with position. These directed variations in chemistry can result in materials with spatially tailored properties. However, when grading between dissimilar alloys or metals, detrimental phases (e.g., brittle intermetallics) may form, providing weak locations within the FGM or complete failure of the FGM by cracking during fabrication. I will describe our approach for combining experiments and computational predictions to develop and validate computational tools toward the design of FGMs that avoid detrimental compositions. I will present results from both equilibrium and Scheil solidification calculations, describing their limitations in light of their ability to predict the experimentally observed phases in FGMs we have investigated.