Microstructural control of additively manufactured Ti6Al4V via in-situ large-area laser annealing

Additively manufactured (AM) alloy Ti6Al4V often exhibits a distinctive alpha/alpha' microstructure due to the high cooling rates associated with AM, which can lead to increased brittleness and necessitate costly post-processing and heat treatment. In this work, we explore the use of layer-by-layer large area surface annealing with a secondary diode laser to control the microstructure of Ti6Al4V during AM and site-specifically induce more ductile, dual-phase alpha/beta Ti6Al4V. Annealing treatments were selected to target sub- and super-beta-transus temperatures at annealed layers, leading to 13 % and 20 % reductions in hardness, respectively, in the 2 mm below the annealed surfaces. Components with rapid switching between annealed and unannealed microstructures were also produced. Temperature measurements at the built surface and base plate were combined with a thermal model to validate microstructural observations, setting the stage for development of full 3-D microstructure and property control using in-situ laser annealing.