Impact of in-situ heat treatment during additive manufacturing of Ti-6Al-4 V on the microstructure and mechanical properties after hot-isostatic pressing

Through adaption of the process parameters during additive manufacturing, the microstructure of Ti-6Al-4V parts can be tailored through post processes. The influence of the energy input, described by the line and the volume energy density as well as the influence of the laser power on microstructural features and the resulting fundamental mechanical properties is shown. Higher energy inputs and laser power leading to higher β-phase contents up to 7.4 vol.% in as-built state and a very fine bimodal to fully lamellar microstructure. Beyond this, hot-isostatic pressing is applied as a secondary heat treatment step, to close low-density defects and tune the properties even further. By adapting the energy inputs during additive manufacturing, the final volume content of precipitation-hardened β-phase can be controlled. This leads to an increase of the material strength of 11% to 1095 MPa in combination with an elongation of 12%. This shows the potential of additive manufacturing as a preliminary heat treatment step for hot-isostatic pressing, allowing defect-free locally adjusted microstructures, which could combine high strength, ductility and toughness.