A novel metric for design of microstructure and mechanical properties in PBF-LB/M Ti6Al4V alloy

Traditionally, volumetric energy density (VED) metric has been the primary tool in design and evaluation of the effect of process optimisation on microstructure and mechanical properties in additively manufactured (AM) components. However, the literature strongly indicates that VED often fails to accurately evaluate this relationship, even for modified versions of VED incorporating materials-specific parameters, such as density or thermal conductivity. This limitation stems from the inability of various VED definitions to account for the heat accumulation in fabricated parts. To overcome this deficiency, we propose a novel metric, normalised energy input rate (NEIR), which incorporates the effect of interlayer time (ILT) on the in-situ heat accumulation during AM process to reflect the microstructural and mechanical properties evolution much more accurately than VED. Further, we demonstrate that NEIR could be used to enable informed site-specific microstructural and microhardness control in laser-based powder bed fusion of metals (PBF-LB/M) of Ti6Al4V alloy, even in extremely thin sections as small as 1 mm in diameter. NEIR has the potential to become the enabling metric for a straightforward design and fabrication of gradient metallic meta-materials with tuneable global response to mechanical loading.