Melt Pool Dimension Control and Its Impact on Microstructure In Electron Beam Additive Manufacturing

Electron beam-based additive manufacturing (EBAM) processes are being seriously considered by the aerospace industry for direct manufacturing and repair applications.  These processes involve use of an electron beam to locally melt a feedstock metal and build up three-dimensional features.  To be successful, these processes must maintain melt pool dimensional control over a wide range of material deposition rates to combine affordability (requiring high deposition rates) with the ability to precisely deposit fine geometries (requiring low deposition rates).  Consistent microstructures must also be maintained, and a long-term goal for these processes has been to relate the control of melt pool dimensions (which can be monitored in real time) to microstructure (which otherwise can only be determined by post-process sectioning and microscopy).  In this research, we present modeling approaches for maintaining melt pool cross sectional area and length-to-depth ratios over beam power and velocity ranges of a factor of 5 or more for Ti-6Al-4V.  Experiments have been carried out on electron beam deposition equipment at NASA Langley and Keystone/Acceleron and results demonstrate the validity of the model predictions.  Control of grain size and grain morphology is also considered over the same range of process variables.  Links are then made between melt pool dimensional control and microstructure control.