In situ absorption synchrotron measurements, predictive modeling, microstructural analysis, and scanning probe measurements of laser melted Ti-6Al-4V single tracks for additive manufacturing applications

Abstract

In this work, the fundamental processing-structure-property (PSP) relationships that govern laser-based additive manufacturing were investigated with the Ti-6Al-4V alloy. X-ray synchrotron imaging carried out in conjunction with in-situ integrating sphere radiometry enabled real-time energy absorption measurements for a range of melting conditions that varied laser power and velocity. A thermal conduction model that incorporated the in-situ absorption data and final melt pool geometry was used to predict the thermal histories and diffusion distances along the heat-affected zone (HAZ) in the Ti-6Al-4V alloy to provide insight into the solid-state phase transformations that occurred in the unmelted regions adjacent to the melt pool. Resulting microstructural features were quantified using scanning electron microscopy techniques to elucidate changes in solidification behavior. Significant changes to α/β-Ti phase fractions were measured in the unmelted HAZ, across all test cases. Nanoindentation and scanning probe microscopy revealed differences in the hardness, modulus, and Volta potential across the resolidified melt pool, HAZ, and wrought base material. These measurements and simulations can be used to predict how processing changes lead to differences in the as-built performance of titanium parts that are used in aerospace and biomedical applications. This work demonstrates the utility of coupling in-situ absorption data with a conduction-only high speed model, which leads reasonable agreement with the synchrotron imaging measurements and microstructural transformations observed herein.