3D printable copper-silver alloys developed for heat transfer applications

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Copper-silver alloy TPMS structures for future studies investigating EV thermal management and impact protection crashworthiness. (Image: Robinson et al.)

Researchers have developed 3D printable copper-silver alloys that they say outperform 3D printed pure silver, pure copper and other commercially available copper materials in strength and heat transfer performance.

The alloys could help meet increasing industry demand for high-efficiency, 3D printable heat transfer materials and devices.

Silver and copper exhibit exceptional thermal properties. For example, silver has the highest thermal conductivity and thermal diffusivity performance properties of any metal, followed closely by copper. However, the high reflectivity and thermal conductivity of these materials create challenges when using them in laser powder bed fusion (LPBF), due to high heat dissipation and laser energy reflection hindering the generation of a melt pool.

Nonetheless, the researchers, from the University of Wolverhampton’s Additive Manufacturing of Functional Materials group, have succeeded in overcoming these challenges using a 400W, 1,060nm fibre laser. Their results will soon be published in the Institution of Mechanical Engineers’ journal: Part L: Journal of Materials: Design and Applications.

Overcoming the reflectivity challenges posed by copper has seen multiple approaches taken in the field of laser materials processing in recent years. For example, lasers in the blue and green wavelengths have emerged that exhibit much higher absorption in copper than infrared lasers. When infrared lasers have been used, however, powers up to the kilowatt level1 have often been required to overcome the challenges posed by the high reflectivity.

When asked then how it was his team was able to process copper and silver using a relatively low power fibre laser, John Robinson, senior engineering technician and the lead researcher of the work, told Laser Systems Europe: ‘We've actually been asked this question many times by laser system manufacturers. We developed both powder bed process and laser parameters simultaneously to optimise laser energy density at the powder bed. The parameters shared in our upcoming publication are really the tip of the iceberg and just the more basic parameters we considered. To explain everything we did would require an entire PhD thesis.’

The researchers used their optimised process to create high-performance alloys that could be printed into thermal management devices, such as triply periodic minimal surface (TPMS) structures for future studies investigating electric vehicle thermal management and impact protection crashworthiness (pictured above).

Dr Arun Arjunan, director of the Centre for Engineering Innovation and Research at the university, said: ‘Thermal management is challenging for many sectors and even small improvements in heat transfer can have a significant impact on reducing material waste while increasing component reliability and life. Additionally emerging systems, such as those in electric vehicles, radio-frequency systems, high power light-emitting diodes, solar cells and solid-state laser light sources, all have significant heat dissipation requirements and therefore innovative materials and advanced manufacturing technologies are essential to create effective thermal management devices of such systems.’ 

The researchers showed that their copper-silver alloys significantly outperform 3D printed pure silver, pure copper and other commercially available copper materials.

For example, their developed copper-silver alloys with 30 per cent silver content demonstrated 84 per cent, 100 per cent and 106 per cent higher yield strengths in comparison to commercially available copper, commercially pure copper, and copper-chromium-zirconium, while their ultimate tensile strength was 91 per cent, 62 per cent and 82 per cent higher. Thermal diffusivity was also shown to increase by 6.2 per cent with silver addition, demonstrating the potential for the development of high-performance copper-silver alloys for heat transfer and thermal management applications.  

‘This is really the first step for the AMFM research group in custom 3D printed thermally-conductive materials,’ said Dr Ahmad Baroutaji, a co-author of the study and the mechanical engineering course leader at the university. ‘Research has already begun on 3D printing materials with exceptional electrical conductivity properties suitable for fabricating induction and electrical windings for electromagnetic applications and electric machines.’

Future work 

Future studies will include continued 3D printing of copper-silver TPMS structures for use in electric vehicles, according to the researchers. The group is also working with collaborators in establishing 3D printed high purity copper and silver with enhanced IEC electrical conductivity for electromagnetic applications.

When asked whether they had any intentions to investigate the use of visible wavelength lasers for their work, the researchers said that while they have been approached by a firm to complete a comparative study using its green laser, they currently have no plans to conduct visible wavelength laser investigations. 

‘However, we are in the process of investigating pulse laser modulation and in the future, we plan to investigate new laser optic technologies such as in process laser spot adjustment and laser beam forming,’ said Robinson. ‘Furthermore, copper purity and feedstock particle distributions are other areas we are looking to investigate.’

[1] Colopi M, Caprio L, Demir AG, et al. Selective laser melting of pure Cu with a 1 kW single mode fiber laser. Procedia CIRP 2018; 74: 59.

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