| Author: | Jin, Shengxi |
| Title: | High-performance copper alloys fabricated by cold spray additive manufacturing |
| Advisors: | Chen, Zibin (ISE) To, Sandy (ISE) |
| Degree: | M.Phil. |
| Year: | 2025 |
| Department: | Department of Industrial and Systems Engineering |
| Pages: | xii, 104 pages : color illustrations |
| Language: | English |
| Abstract: | Copper and its alloys are critical materials in thermal and electrical industries due to their outstanding thermal and electrical conductivity. Their ability to efficiently transfer heat and electricity makes them indispensable in applications such as heat exchangers, electrical wiring, and electronic components. With the rapid development of high-end industrial components, the complexity of copper parts has extensively increased. Traditional manufacturing methods, such as casting and machining, often struggle to produce intricate designs cost-effectively. Additive manufacturing (AM) has emerged as a promising solution, offering design flexibility and reduced material waste. Among AM techniques, cold spray additive manufacturing (CSAM) stands out as a solid-state deposition process that minimizes thermal distortion and oxidation, making it ideal for producing high-quality copper components at a lower cost compared to laser-based AM methods. Despite its advantages, cold-sprayed copper suffers from inferior mechanical properties, such as low strength and hardness, which limit its use in structural and high-load applications. Conventional approaches, such as incorporating hard ceramic particles or intermetallic compounds into the copper matrix, improve mechanical performance but drastically reduce thermal and electrical conductivity—key properties that make copper desirable in the first place. Therefore, alternative strengthening strategies must be developed to overcome this limitation without compromising the intrinsic advantages of copper. This thesis aims to design and fabricate novel copper alloys via CSAM that achieve enhanced mechanical properties without sacrificing thermal and electrical conductivity. By optimizing alloy composition and processing parameters, the research seeks to develop materials that meet the demanding requirements of modern industrial applications. The successful implementation of such alloys would expand the use of CSAM in producing high-performance copper components, offering a cost-effective and efficient solution for advanced thermal and electrical systems. Chapter 1 provides an overview of the distinctive properties of copper and its alloys, along with their key industrial applications. Subsequently, it introduces CSAM, covering its historical development, deposition and bonding mechanisms, and current applications. Finally, the research challenges addressed in this thesis are outlined. Chapter 2 details the experimental methodologies employed in this study. The sample preparation process is described, followed by an explanation of advanced electron microscopy techniques used for microstructural characterization, including scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and scanning transmission electron microscopy. Additionally, the procedures for mechanical property testing, thermal and electrical conductivity measurements, and finite element method simulations are discussed. Chapter 3 investigates a novel strategy to enhance the mechanical properties of cold-sprayed Cu while retaining its high conductivity through the introduction of Cu₂O nanoprecipitates. In this chapter, oxygen was introduced during the cold spray process to form Cu₂O precipitates within the Cu matrix. These precipitates strengthen the material with a yield strength of 480 MPa while maintaining exceptional thermal conductivity (310 W/m·K) and electrical conductivity (85.5% IACS). The precipitates pinned at grain boundaries effectively hinder the recovery and grain growth, thereby promoting the grain refinement and dislocation multiplication. This study presents a new approach for designing high-performance Cu-O alloys via nanoscale precipitate engineering, demonstrating significant potential for industrial applications. Chapter 4 explores the fabrication of Cu-Sn alloys with superior compressive properties using CSAM. Bronze (Cu-Sn alloys) has been extensively utilized across industries throughout history. However, insufficient cooling rates in conventionally manufactured bronze often facilitate the formation of brittle δ-phase (Cu₄₁Sn₁₁) segregations that degrade mechanical properties. To overcome this limitation, CSAM was employed to deposit Cu-Sn alloys with controlled Sn content (5 wt.% and 10 wt.%) using pre-alloyed feedstock powders. The high deposition temperature and rapid cooling inherent to CSAM effectively suppressed δ-phase segregation. Notably, the heterogeneous Sn distribution in the Cu-10Sn alloy contributed to exceptional compressive performance (yield strength of approximately 1 GPa) compared to Cu-5Sn and pure Cu. The higher Sn content lowers the recrystallization temperature of the alloy, thereby advocating the dynamic recrystallization during cold spray. The promoted grain refinement effect cooperated with segregated intermetallic compounds to enhance the mechanical properties of the as-sprayed Cu-10Sn alloys. This study demonstrates the feasibility of producing high-strength Cu-Sn alloys via CSAM while elucidating microstructural changes during deposition. Chapter 5 summarizes the key findings of this research and proposes future directions for further investigation. |
| Rights: | All rights reserved |
| Access: | open access |
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