Microstructural evolution in laser directed energy deposited Ti-8.5Cu alloy: Insights from Synchrotron X-ray imaging

Additive manufacturing often results in a heterogeneous microstructure along the build direction due to uneven thermal histories, significantly impacting the final material properties. This study investigates how the build process influences microstructural evolution in Ti-8.5Cu alloy using Directed Energy Deposition – Laser Beam/Metals (DED-LB/M). The research utilises in-situ synchrotron X-ray radiography to observe changes in melt pool geometry layer by layer. Our findings reveal a strong correlation between the melt pool dimensions and the microstructural features, such as grain size and phase fractions, along the build direction and across different process conditions. Notably, melt pool sizes increase from the bottom to top layers and vary with process parameters, reflecting a rise in residual temperature. These data are used to calibrate the classical Rosenthal model, enabling it to describe the temperature profile across the entire build accurately. This study provides key insights into Ti-8.5Cu alloy microstructure control during DED-LB/M processing and demonstrates the powerful capabilities of in situ synchrotron X-ray imaging for understanding complex manufacturing processes.