Microstructure control in additively manufactured Ti-6Al-4V during high-power laser powder bed fusion

Laser powder bed fusion (LPBF) is a premier additive manufacturing (AM) process capable of making intricate metallic parts with short lead time, but its widespread industrial acceptance is still limited due to its low build rate in producing high-quality near net-shape parts. Herein, we have demonstrated the capability of employing high laser power LPBF for the manufacture of quality Ti-6Al-4V at a much-increased build rate, combined with decent dimensional accuracy, suitable microstructure, and superior mechanical performance. Compared to LPBF under low laser power (≤ 400 W), high laser power (600 W) LPBF offers a much narrower processing window to reach a balance among dimensional accuracy, materials density, and desired microstructure. For a given high laser power, a combination of low scanning speed, small hatch spacing, and small focal offset distance imparts a thermal environment with reduced cooling rates to facilitate the formation of lamellar α+β or globular α microstructures at a much lower critical energy density than that under low power. The findings in this work advance our understanding of optimizing the LPBF process in the high-power regime towards sustainable and efficient manufacturing of quality Ti-6Al-4V components having superior mechanical performance.