Microstructural evolution and mechanical properties of dissimilar structures manufactured by additive manufacturing
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Type
ThesisThesis type
Doctor of PhilosophyAuthor/s
Razzaq, SamiaAbstract
The joining of dissimilar metals is vital in aerospace, electronics, and energy systems, where combining materials with complementary properties enhances component performance. Conventional fusion welding often struggles with metals that differ in thermal and metallurgical behaviour, ...
See moreThe joining of dissimilar metals is vital in aerospace, electronics, and energy systems, where combining materials with complementary properties enhances component performance. Conventional fusion welding often struggles with metals that differ in thermal and metallurgical behaviour, leading to defects such as intermetallic compound (IMC) formation, porosity, and weak mechanical integrity. Additive manufacturing (AM), particularly Wire Arc Additive Manufacturing (WAAM), offers an alternative due to its controlled heat input, high deposition rates, and suitability for large, near-net shape components. This thesis investigates WAAM-based joining of 316L stainless steel with Nimonic 90 and with pure copper (Cu) using two deposition strategies: Type I (layer by layer) and Type II (zigzag/overlapped). Microstructural analysis confirmed defect free bonding in both systems, with no cracking, porosity, or brittle IMCs. In 316L–Nimonic 90 joints, Fe–Ni solid solutions and TiC precipitates formed, with Type II interfaces showing broader diffusion zones and higher hardness. In 316L–Cu joints, dual phase interfaces of FCC γ Fe and FCC Cu developed due to immiscibility and rapid thermal cycling, with fractures occurring on the Cu side, indicating strong interfacial adhesion. Mechanical testing showed that both material pairs exceeded the tensile and yield strengths of their softer base metals. Type II interfaces demonstrated superior performance due to enhanced elemental mixing and interlocking microstructures. However, 316L–Cu joints showed reduced ductility because of deformation mismatch and grain coarsening in the Cu region. Overall, this work demonstrates that WAAM can produce robust dissimilar metal joints and highlights the role of deposition strategy in controlling interfacial microstructure and mechanical properties, supporting the development of reliable multi material components for next generation manufacturing.
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See moreThe joining of dissimilar metals is vital in aerospace, electronics, and energy systems, where combining materials with complementary properties enhances component performance. Conventional fusion welding often struggles with metals that differ in thermal and metallurgical behaviour, leading to defects such as intermetallic compound (IMC) formation, porosity, and weak mechanical integrity. Additive manufacturing (AM), particularly Wire Arc Additive Manufacturing (WAAM), offers an alternative due to its controlled heat input, high deposition rates, and suitability for large, near-net shape components. This thesis investigates WAAM-based joining of 316L stainless steel with Nimonic 90 and with pure copper (Cu) using two deposition strategies: Type I (layer by layer) and Type II (zigzag/overlapped). Microstructural analysis confirmed defect free bonding in both systems, with no cracking, porosity, or brittle IMCs. In 316L–Nimonic 90 joints, Fe–Ni solid solutions and TiC precipitates formed, with Type II interfaces showing broader diffusion zones and higher hardness. In 316L–Cu joints, dual phase interfaces of FCC γ Fe and FCC Cu developed due to immiscibility and rapid thermal cycling, with fractures occurring on the Cu side, indicating strong interfacial adhesion. Mechanical testing showed that both material pairs exceeded the tensile and yield strengths of their softer base metals. Type II interfaces demonstrated superior performance due to enhanced elemental mixing and interlocking microstructures. However, 316L–Cu joints showed reduced ductility because of deformation mismatch and grain coarsening in the Cu region. Overall, this work demonstrates that WAAM can produce robust dissimilar metal joints and highlights the role of deposition strategy in controlling interfacial microstructure and mechanical properties, supporting the development of reliable multi material components for next generation manufacturing.
See less
Date
2026Rights statement
The author retains copyright of this thesis. It may only be used for the purposes of research and study. It must not be used for any other purposes and may not be transmitted or shared with others without prior permission.Faculty/School
Faculty of Engineering, School of Aerospace Mechanical and Mechatronic EngineeringAwarding institution
The University of SydneyShare