Dissimilar Material Mixing in Laser Powder Bed Fusion Additive Manufacturing 168 views

Laser Powder Bed Fusion (LPBF) is a metal additive manufacturing (MAM) technique that enables the direct fabrication of composite structures and the joining of dissimilar materials. Unlike conventional methods such as welding, which often struggle with joining materials of vastly different thermophysical properties or result in brittle intermetallic formation, LPBF offers precise, layer-by-layer control over composition and geometry. Through strategies such as compositional gradients, engineered interlayers, or tailored build paths that intentionally leverage intermetallic formation, LPBF circumvents many of the limitations encountered in traditional dissimilar material joining. As feedstock design becomes increasingly important, the use of pre-mixed elemental powders for in-situ alloying is emerging as a promising alternative to costly pre-alloyed powders. However, a significant knowledge gap remains regarding the relationship between process parameter control and elemental mixing efficiency in LPBF. Moreover, existing methods for quantifying melt pool heterogeneity are often limited in resolution and accuracy. This thesis addresses these gaps by proposing a novel mathematical framework to quantify chemical heterogeneity in the Al-Zn system—a common soluble system. Additionally, a two-regime analysis of the immiscible Cu-Fe system is conducted to elucidate the mechanisms of mixing, melt pool morphology, and microstructural evolution. The key driving forces for elemental mixing are identified as Marangoni convection and recoil pressure, with scan velocity found to play a dominant role in determining mixing efficiency, while laser power primarily affects melt pool volume and vaporization, with secondary effects on mixing. Overall, this work advances the understanding of process-structure relationships in dissimilar material systems under LPBF and provides a foundation for optimizing in-situ alloying strategies for both soluble and immiscible alloy systems.

MS (Master of Science)

additive manufacturing; laser powder bed fusion; dissimilar material joining; metallurgy

English

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2025-07-29