Understanding the effect of scanning strategies on the microstructure and crystallographic texture of Ti-6Al-4V alloy manufactured by laser powder bed fusion

Abstract

In this work, experimental and numerical approaches are performed to explore the influence of scanning strategies on the microstructure, crystallographic texture as well as the mechanical behavior of Ti-6Al-4V alloy manufactured by Laser Powder Bed Fusion (LPBF). In-situ monitored data of the energy intensity show that different scanning strategies result in variations of energy intensity distribution. The characterization of the microstructure and crystallographic texture reveals that the sample with hexagon scan pattern displays the structure with columnar primary β phase, while the specimens with chessboard scan exhibit equiaxial-like morphology. EBSD and TEM results provide evidence of the appearance of residual β nanoparticles. A finite element model is developed to further explain the phase transformation during LPBF and the formation mechanism of residual β particles. The numerical results indicate that the appearance of the residual β phase is attributed to the preheating/reheating effect by the adjacent tracks and successive layers, and the final phase composition of the LPBF-built Ti-6Al-4V alloy combines the α′, α, and β phases. Findings in the present paper show that various scanning strategies lead to a clear diversification in the microstructure, crystallographic texture, and phase composition of LPBF-built samples, which opens a route towards the tailoring of mechanical properties and isotropic behaviors in additive manufacturing.