Laser intensity profile as a means to steer microstructure of deposited tracks in Directed Energy Deposition

Abstract

In Laser-based Directed Energy Deposition (L-DED) the laser-induced spatial and temporal thermal cycles strongly determine the microstructure of deposited layers. The effect of three different laser intensity profiles (beam shapes) on the shape of the melt pool and the resulting microstructure was studied. To this end, thermal gradients and growth rates, derived from measured melt pool emissions, are compared to characteristics of the microstructure in the deposited tracks. These characteristics are obtained using Electron Back Scatter Diffraction (EBSD). It was found that the shape of the laser beam strongly affects the melt pool morphology. Therefore it affects also the solidification characteristics and thus the resulting microstucture. Correlations are found between the thermal gradient - growth rate ratios and the grain shapes and amount of texture. Hence, the beam profile is a tool to steer the microstructure of deposited parts during L-DED.

Keywords

• Directed energy deposition
• Laser beam shape
• EBSD
• Melt pool imaging
• Stainless steel