Investigation of powder-based directed energy deposition for multi-material manufacturing

Abstract

Interest in additive manufacturing (AM) has expanded rapidly, with Directed Energy Deposition (DED) emerging as a prominent technique for fabricating large-scale components, refurbishing parts, and enabling multi-material deposition. Powderbased DED is governed by a complex interplay of physical phenomena, including particle–particle, particle–gas, and particle–wall interactions within the nozzle, as well as particle–laser interactions during melt pool formation. When dissimilar metallic materials are used, additional challenges arise from differences in particle density, morphology, flowability, thermal properties, melting behavior, and interfacial reactions. Therefore, understanding powder delivery, interfacial formation, and melt pool behavior is essential for improving the stability and reliability of multi-material DED processes. This thesis investigates powder-based DED for multi-material manufacturing through three connected studies. The first study investigates the powder stream behavior of two dissimilar metal powders, stainless steel SS316L and bronze CuSn10, during powder feeding through a coaxial DED nozzle. High-speed imaging combined with particle image velocimetry is employed to characterize the powder stream geometry and the particle velocity distribution under different processing conditions. The influence of powder feeding rate, carrier gas flow rate, and shielding gas flow rate on the focal distance, stream waist, and convergence angle of the powder stream is systematically analyzed. Image-processing techniques are used to extract the geometric characteristics of the powder stream, enabling a quantitative comparison between the two powder materials. The results reveal distinct differences in particle flow behavior due to variations in particle density, size, and morphology, highlighting the critical role of gas flow parameters in controlling powder stream stability and delivery efficiency....