Anisotropic material properties of pure copper with fine-grained microstructure fabricated by laser powder bed fusion process

Abstract

With excellent thermal and electrical conductivity, pure copper has been widely used in many industries. The development of additive manufacturing (AM) enables the prototyping of copper components rapidly and cost-effectively. Especially, Laser powder bed fusion (LPBF), one of the AM techniques, now can fabricate pure copper components with complex geometries. However, the high reflection of laser energy in pure copper at the wavelength used in most commercial fiber laser AM machines poses a challenge in industry practice. To circumvent this problem, higher laser power, different laser wavelength, or different energy source (such as electron) have to be adopted, which alleviates the problem of low laser energy absorptivity, but leads to the undesirable tradeoff between the mechanical properties and thermal/electrical performance. In the current study, the high-precision LPBF (HP-LPBF) combining fine beam and small layer thickness managed to achieve enhanced strength and ductility, while keeping the thermal and electrical conductivity close to the annealed one without heat treatment. Utilising small layer thickness with scan strategy of 67° rotation angle, the columnar grain growth was inhibited, which weakened the anisotropy of material properties. As a result, pure copper by HP-LPBF outperforms those by conventional PBF in mechanical, thermal, and electrical properties with reduced anisotropy.