Influence of carbon on the rheology and additive manufacturability of Ti-6Al-4V powders

• Ti6Al4V powder properties become significantly worse over 0.50 wt% C inclusion. • Agglomeration of carbon around satellite particles increases cohesion reducing flow. • Carbon addition within 0.25 wt% produces high density parts with < 0.10 % porosity. • Printed parts have similar acicular α’ martensitic microstructure with no carbides. • Grade 23 exhibits better powder-part properties after carbon addition than Grade 5. The focus of this work was to determine the effect of carbon blending on powder-part properties of titanium alloy Ti-6Al-4V. To assess this, carbon blends of both grade 5 and grade 23 from 0.1-1.0 wt% C were prepared. Part printability using laser powder bed fusion (LPBF) was assessed by measuring the segregation, flowability, rheology, and spreadability of the powder. Blend quality was assessed chemically and visually via computed tomography and scanning electron microscopy. Carbon blends above 0.25 wt% C produced significant segregation of carbon particles. Agglomerated carbon segregates acted as barriers to flow causing the reduction in dynamic flow by 40–60% compared to the virgin powders. High carbon contents also limited powder spreadability by promoting large streaks during powder spreading. Below 0.25 wt% C, the deleterious effects of segregation, flowability, and spreadability were reduced and the powder characteristics were comparable to the processable virgin powders. Printed parts exhibited very small effect of carbon blending on the density and micro-hardness of the material. The grade 23 powder is more suitable for carbon blending and offers the highest part densities and lowest variation in material hardness. This is attributed to lesser carbon agglomeration, better powder flow, and fewer interstitial elements.