Effects of high deposition rate during cold metal transfer additive manufacturing on microstructure and properties of Ti-6Al-4V

E. Farabi, T. Klein, M. Schnall, S. Primig
Additive Manufacturing 71 (2023) 103592. (OPEN ACCESS)

Wire-arc directed energy deposition (waDED) of Ti-alloys via the cold metal transfer (CMT) offers a new additive manufacturing (AM) pathway for 3D printing large-scale aerospace components with higher production rates and reduced costs. Despite several benefits, high-speed AM processes involve increased heat input and complex thermal profiles, resulting in heterogeneous microstructures and anisotropic properties for Ti-alloys. Therefore, transforming this promising technology into a desirable manufacturing process for additional industries and applications requires practical CMT process design approaches that resolve the remaining challenges.

This work is one of the first studies on a newly developed CMT strategy that utilizes higher deposition rates and lower heat inputs. We investigate the microstructure evolution during CMT of the critical Ti-6Al-4V alloy and establish a fundamental understanding on the process-microstructure-property relationships. The constant stirring of the melt pool and unique thermal profile of the CMT process are shown to break the epitaxially grown β grains, refine both α and β- phase structures and promote elemental partitioning. The microstructure is dominated by three α-variant clusters that contribute to nucleation and refinement of β grains during thermal cycles. This microstructural refinement unlocks more isotropic mechanical response when compared to other AM techniques while the chemical partitioning leads to variations in α-lath size and local mechanical heterogeneities with negligible effect on the overall performance of the Ti-6Al-4V build.