Morphological characterisation of recycled powder and microstructures of Ti-6Al-4V components synthesized by LENS additive manufacturing

Abstract

Direct Metal Laser Deposition (DMLD) processes such as LENS are gaining ground in commercial manufacturing processes of functional end-products. This is attributed to this process being popularized as a sustainable technology with the potential to substitute the energy intensive, wasteful and environmentally unfriendly traditional techniques. However, during processing a significant fraction of the injected powders do not end up as part of the final component. The properties of these powders change due to heating resulting in coalescence and possible chemical reactions with the surrounding environment. A potential way to overcome this is by adopting an effective powder recycling procedure by which material use efficiency can be improved. Even so, these changes may have detrimental impact on the mechanical properties of the end-product. The objective of this paper is to investigate the effect of powder recycling on mechanical properties as a consequence of a change in powder characteristics. The potential for improving the LENS process by powder recycling process has been evaluated by comparatively studying the feedstock characteristics, i.e. morphology, particle size distribution and microstructure of powders in as received state and after laser exposure during repeated deposition cycles. Microstructures, micro-hardness and Density of the built samples were measured after the first deposition-normalization-reuse cycle. The results revealed a correlation between the powder characteristics and the properties of the corresponding built sample used for that specific deposition.