Morphological induced improvements in the bulk mechanical properties of chemically etched additively manufactured Ti-6Al-4V micro-struts

Powder Bed Fusion (PBF) additive manufacturing techniques have enabled the fabrication of geometrically complex porous metallic lattice structures. Despite the many advantages of this approach, surface and near surface defects inherited from the fabrication process act to limit their structural and mechanical integrity. Consequently, surface cleaning techniques such as chemical etching have been increasingly adopted post process. Although the benefits of this technique have been captured across a range of lattice structures, the existing body of work is typically a characterisation of the engineering mechanical properties of lattices, rather than the bulk mechanical properties of the material. From a design perspective, characterisation of such properties is fundamental to prediction of mechanical performance and failure mechanisms.

In this study, standardised micro-strut dog-bone geometries were adopted as a means of isolating geometrical variations between lattice designs; allowing us to study the bulk mechanical properties of the material. Incremental etching was conducted and changes to both the surface and morphological properties of the micro-structs was characterised. Improvements in these factors was associated with a corresponding increase in mechanical properties. Both strength and stiffness increased following removal of process inherited surface defects, which can be linked to a removal of non-load bearing material. Failure strain and fatigue resistance also improved following surface etching, although similar fracture surfaces were observed in both groups. Together these findings demonstrate the benefits of chemical etching for improving the mechanical properties of additively manufactured Ti-6Al-4V lattice structures.