The processing of pure copper (Cu) in the powder bed fusion laser beam (PBF-LB) process has been a focus of research in recent years in the field of laser based additive manufacturing. Cu reflects 97% of the radiation at a commonly used redlight laser wavelength of 1064 nm [1]. There are various solutions such as reducing the wavelength, increasing the energy density and increasing the absorption by alloying and coating the powders. In this study, the Cu powder surface was covered with sub-micrometer tungsten (W) particles to increase the absorptivity of the powder. The advantage of W is its insolubility in Cu [2]. Alloying Cu with additives decrease its thermal and electrical properties enormously. Two routes were developed to manufacture the powders. The first route of manufacturing Cu/W-powder was by means of a milling process using mechanical connection. The second manufacturing method was a co-injection atomization where a separate W particle jet is sprayed into the primary liquid Cu particle jet. This allows the Cu/W-composite to be manufactured in a single production step. The powders were produced and sieved in an inert atmosphere of nitrogen and analyzed with a combination of laser diffraction and scanning electron microscopy.

Test specimens were manufactured by a PBF-LB machine with a volume energy density of 171 J/mm³. The relative density was measured both optically and using the Archimedes principle. The optical method yielding values in the range of 95% to 99%. The thermal diffusivity was analyzed by laser flash analysis and thermal-optical measurement. By eddy current measurement, the electrical conductivities of the specimens were determined. Also, the Vickers hardness was measured. It could be shown that 87% of thermal conductivity and 86% of electrical conductivity could be achieved compared to the pure copper.

References

[1] D., Becker; Dissertation, Apprimus Verlag, Aachen, 2014, p. 42.

[2] P. R., Subramanian; D. E., Laughlin; Phase Diagrams of Binary Tungsten Alloys; Indian Institute of Metals, Calcutta, 1991, p. 76.