The effects of microporosity in struts of gyroid lattice structures produced by laser powder bed fusion

Additive manufacturing by laser powder bed fusion allows the production of complex parts including lattice structures in popular metal alloys such as Ti6Al4V. Lattice structures are a class of meta-materials which hold many advantages such as the possibility for the production of lightweight parts with tailored mechanical and other properties: these have many potential applications in aerospace and medical fields. The laser powder bed fusion process can result in microporosity inside the produced material, which can affect the mechanical performance of these types of materials. In this work, different typical microporosity distributions are induced in manufactured gyroid lattice structure samples and the mechanical performance is tested by both static compression and compression-compression fatigue. X-ray tomography was used to validate the microporosity distributions and samples were tested in stress-relieved state and hot isostatic pressed state. In particular, it is found that small amounts of keyhole mode microporosity of ~0.2% make no difference while lack of fusion is critical, especially when this results in inefficient HIP pore closure. The results highlight the effect of microporosity on the mechanical performance of these materials and the results add to the knowledge base and trustworthiness of these materials. © 2018 The Authors