Powder reuse and its contribution to porosity in additive manufacturing of Ti6Al4V

Abstract

Powder reuse has become a central issue in the pursuit to industrialize metal Additive Manufacturing (AM). Furthermore, build porosity is a critical concern to component reliability and damage tolerance of the metal. However, the contributions of powder reuse to metal porosity has received very limited attention. In this study, the porosity resulting from Powder Bed Fusion-Electron Beam Melting (PBF-EB) AM of Ti6Al4V was characterized over a series of 30 build cycles (consisting of ~ 480 h cumulative build time) using X-ray Micro Computed Tomography (μCT). Investigated were the volume fraction of pores (i.e. the porosity), as well as the pore size, shape, and spatial distribution. The most prevalent pores identified were: i) those originating from the gas atomized powder, and ii) those caused by incomplete fusion of the melt pool. Although there was a minor reduction in the pore size distribution with powder reuse, the overall average volumetric porosity was 0.10 ± 0.02% and there was no significant change with increasing reuse. An inverse relationship between pore diameter and sphericity was found, with large pores posing greater effective stress concentration. Whereas the greatest pore density was located at the transition between the contour and melt beams, approximately 0.5–1.0 mm adjacent to the surface of parts, the largest pores were located within the interior hatching region. Hence, despite progressive deformation of the particles and an increase in oxidation, there was no discernable change in metal porosity with powder reuse in PBF-EB AM of Ti6Al4V.