Abstract | Keywords | Export | Availability | Bookmark

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Laser powder bed fusion (LPBF) is one of the most common additive manufacturing (AM) ‎techniques for fabricating various components in different industries. In recent years, ‎fabricating a single component with a multi-material structure has become increasingly ‎prevalent. It allows a combination of dissimilar materials with different properties into one ‎component to obtain a unique function. However, the fabrication of multi-material parts with ‎complex geometries via conventional methods is difficult due to their inherent limitations. ‎Multi-material LPBF offers a new route for producing 3D objects with tailored properties. ‎Despite its numerous advantages, the achievement of a free-defect interface between ‎dissimilar materials can be the main challenge.‎ Among multi-metallic materials, the stainless steel (SS)-copper (Cu) combination is very ‎attractive due to the excellent thermal conductivity of Cu combined with the good mechanical ‎properties and corrosion resistance of SS. This study explores the multi-material LPBF of 316L-‎CuCrZr components. The LPBF fabrication of SS-Cu multi-material parts is very challenging ‎because of their significant difference in properties such as solubility, laser absorptivity, ‎melting points, and thermal expansion coefficient, resulting in defects such as cracks and ‎pores at the interface after LPBF processing. ‎ In this work, two potential techniques for resolving the interfacial defect issues were ‎investigated. ‎ The first potential solution was surface modification of CuCrZr powder by chromium diffusion ‎in a nitrogen atmosphere to increase the laser absorptivity of the copper-rich powder. The ‎‎316L-modified CuCrZr samples were printed in various conditions. Some SS-Cu samples were ‎stacked horizontally with different scanning sequences and with different Cu printing ‎parameters. In addition, some SS-Cu samples were stacked vertically with different CuCrZr ‎LPBF scanning parameters, different interface designs and strategies, as well as the application ‎of interface remelting strategies. In all samples, however, microcracks were observed at the ‎interface between SS and Cu near the SS side, originating from Fe-rich regions. ‎ Another novel method to resolve the cracking problem was introducing a Ni-based interlayer. ‎In this thesis, an Inconel 625 interlayer with variable thickness was deposited between the ‎‎316L and CuCrZr alloys. The microstructure, elemental distribution, and grain size and ‎orientation of the multi-metallic samples were characterized. The results exhibited that the ‎addition of a 40 µm thick interlayer does not have a tangible effect on eliminating crack ‎formation. When increasing the interlayer thickness to 80 and 160 µm the number and size of ‎microcracks significantly decreased in the Cu-Ni-Fe intermixing zone. The microcracks were ‎mainly located at high-angle grain boundaries (>15°) and partially filled with copper. Finally, ‎applying a Ni-based interlayer with a thickness of 240 µm could successfully eliminate the ‎formation of microcracks. A further increase of the interlayer thickness to 320, 400, and 480 ‎‎µm, still guaranteed the formation of crack-free interfaces. In all samples with Ni-based ‎interlayers of at least 240 µm, no Fe was found near the interface between the Ni and Cu ‎alloys, indicating that the interlayer thickness in crack-free samples was sufficient to avoid the ‎presence of Fe-rich regions near the interface.