Single point exposure LPBF for the production of biodegradable Zn-alloy lattice structures

Abstract

The processing of Zn alloys through Laser Powder Bed Fusion (LPBF) with conventional vector-based scan strategies poses significant challenges regarding process stability. The evaporation tendency of such materials limits the quality of the process outcome introducing excessive porosity and low geometrical accuracy. Commonly, this issue requires a modification on the hardware of the LPBF machine concerning the gas management. The process instability and excessive vapour generation can be avoided also with a careful control of the laser energy deposited over time. Hence, this study focuses on the novel scan strategies as a possible solution. Single Point Exposure (SPE) scan strategy was applied to process Zn-0.5Mg powders, allowing to suppress the excessive smoke formation in the printing of body centred cubic (BCC) cell lattice structures. The new strategy was developed via an open LPBF system, together with dedicated slicing software for laser path and parameter assignment. The laser pulse profiles were characterized with a fast photodiode in the SPE control mode. Lattices with strut diameters smaller than 200 µm could be obtained, proving the capability of the strategy in the processing of fine features on challenging materials such as Zn alloys maintaining process stability. The lattice struts were adequately densified without excessive porosity and the relative density of the lattices was controlled between 2% and 35% by means of the process parameters and cell size. The obtained samples were also characterized regarding their mechanical properties, in view of future applications in load-bearing biodegradable implants.