The feasability of processing silver and copper using 400w laser powder bed fusion additive manufacturing
AffiliationSchool of Engineering, Computing and Mathematical Sciences, Faculty of Science and Engineering
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AbstractThe combined effect of accelerating climate change and the COVID-19 pandemic have resulted in governments globally placing greater emphasis on innovations in healthcare, materials science, sustainable manufacturing, and green energy solutions. Global requirements for reducing greenhouse gas emissions alongside governmental commitments regarding the development of a healthier, safer, and greener future across sectors including healthcare, energy, transport, and buildings has resulted in recent advances in low emission vehicles, renewable energy sources, healthcare, and energy capture technologies. However, it is widely agreed that many industries will require advances in materials and manufacturing technologies for effective solutions for future systems and devices. Silver (Ag) and copper (Cu) exhibit exceptional thermal, electrical, and antimicrobial characteristics and offer much potential for superior performance materials, devices, and systems. Additionally, recent developments in Computer Aided Design (CAD) and simulation techniques, design tools, custom materials, and Additive Manufacturing (AM) technologies open up possibilities to manufacture superior performance component geometries not previously possible with more traditional manufacturing technologies. Consequently, combining Cu and Ag material characteristics with AM design freedoms present significant prospects for many industries. For metal AM the Laser Powder Bed Fusion (L-PBF) process is the most mature technology and is commonly utilised in aerospace, automotive and healthcare sectors. However, L-PBF processing highly reflective and thermally conductive Cu and Ag is challenging due to their reflective nature resulting in insufficient energy absorption at the powder bed and it is generally agreed that L-PBF processing Cu and Ag with acceptable densities requires nonstandard higher power infrared lasers (>500W), small spot size lasers, different wavelength lasers and/or material alloying. In this regard this research reports the feasibility of processing high purity Cu, Ag and Cu-Ag alloys (utilising a standard 400W L-PBF system) for thermal, electrical, and antimicrobial applications. Initially optimum laser parameters were developed demonstrating the feasibility of successful L-PBF processing high purity Ag and the effects of L-PBF parameters on material density and mechanical performance are established using X-ray Computed Tomography (XCT). Porosity morphology, content and distribution varied significantly as energy density at the powder bed was altered through L-PBF parameter adjustment, which in turn effected density and mechanical performance. Ag density and number of pores achieved were 86.5% to 99.8% and 166 to 3421 respectively. While L-PBF Cu is shown to have comparable yield strength (161.04 MPa) to commercially available L-PBF Cu alloys when comparing Cu and Ag the L-PBF Ag exhibited higher failure strain yet significantly lower yield strength and UTS with Cu being 109% and 59% higher in comparison to Ag. Subsequently Cu-Ag in situ alloying is utilised to investigate the addition and alloying of Ag to Cu and resultant mechanical performance for as built and annealed alloys reported. Ag addition in Cu increased yield strength and UTS significantly with all Cu-Ag alloys outperforming Ag, Cu and all commercially available Cu materials evaluated. CuAg10% reported yield and UTS increases of 39% and 41% in comparison to L-PBF Cu. 20% Ag addition saw increases of 75% and 72% from Cu while 30% Ag addition exhibited 105% and 94% higher yield strength and UTS. Thermal performance of Ag is shown to significantly outperform Cu and Cu-Ag alloys exhibiting 70% higher thermal diffusivity in comparison to Cu even with significantly higher porosity content. For electrical performance sample density driven by powder particle PSD was the biggest contributing factor to improved performance. Small Cu purity changes could not be directly defined with the highest purity Cu (>99.98%) resulting in similar electrical performance (being 59.7% and 59% of the International Annealed Copper Standard (IACS)) compared to the lowest purity Cu (>99%) assessed. Antibacterial and antiviral investigations of Cu and Ag show that L-PBF Ag not only inhibits bacterial growth but displays a 99.9% kill of the most common implant infection-causing Staphylococcus aureus in 14 hours while the addition of W and Ag as alloying elements to L-PBF Cu results in superior antiviral properties with 100% inactivation of SARS-CoV-2 in 5 hours. Contrary to recent literature and commonly agreed understanding regarding L-PBF processing of Cu and Ag the work undertaken in this thesis demonstrates the feasibility of L-PBF processing highly reflective Cu and Ag for thermal, electrical, and antimicrobial applications utilising a standard 400W L-PBF AM system.
CitationRobinson, J. (2021) The feasability of processing silver and copper using 400w laser powder bed fusion additive manufacturing. University of Wolverhampton. http://hdl.handle.net/2436/624968
PublisherUniversity of Wolverhampton
TypeThesis or dissertation
DescriptionA thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of Philosophy.
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