Achieving high strength in LPBF - Deposited Ti6Al4V-5Cu via tailoring volumetric energy density

Laser powder bed fusion (LPBF) effectively overcomes the drawbacks of conventionally cast Ti-Cu alloys. Nevertheless, prior research has predominantly centered on the impact of Cu addition levels, leaving the effect of volumetric energy density (VED) on the alloy's microstructure and mechanical performance insufficiently investigated. This study investigates the effect of VED on the microstructure evolution and mechanical properties of Ti6Al4V-5Cu alloy fabricated by LPBF. Ti6Al4V-5Cu specimens were fabricated with VED ranging from 57 to 138 J/mm³, and Ti6Al4V specimens were produced under identical process parameters as a control for the sample with the maximum ultimate tensile strength (UTS). The results show that all printed alloys were mainly composed of acicular α' martensite, while the addition of Cu introduced Ti₂Cu precipitates and significantly refined the martensitic structure. As VED increased, the α′ martensite became progressively coarser, and the prior β grains evolved from coarse columnar grains to finer columnar and nearly equiaxed morphologies. Meanwhile, Ti₂Cu precipitation was promoted by enhanced thermal cycling, changing from barely detectable nanoscale precipitates at low VED to more obvious granular precipitates at higher VED. The Ti6Al4V-5Cu alloy fabricated at the lowest VED exhibited the highest ultimate tensile strength of about 1580 MPa, but showed limited elongation due to continuous α_GB and Ti₂Cu lamella. Increasing VED reduced strength but partially restored ductility. These findings clarify the relationship between LPBF energy input, Ti₂Cu precipitation, and the strength–ductility response of Ti6Al4V-5Cu alloys.