Enabling Microstructure Manipulation in Laser Powder Blown Directed Energy Deposition

Laser powder-blown directed energy deposition (DED-LB) has become known for its flexibility in geometry and materials, demonstrated by its propensity for 5-axis fabrication, functionally graded materials, and repair applications. During deposition of material, the laser beam shape directly affects the temperature distribution across the melt pool. Grain growth and resulting microstructure can be manipulated by utilizing different laser beam shapes which affect solidification conditions. To better understand the relationship between beam shape and microstructure in DED-LB, IN265 was deposited in single tracks using a multi-mode laser with both Gaussian and Ring mode laser distributions (nLight AFX-1000). Seven modes were investigated where the power ratio between the Gaussian mode and Ring mode was varied from 0/100 to 90/10. Resulting material structure was investigated using optical imaging and Electron Backscatter Diffraction (EBSD) to connect process changes to microstructure. A duplicate set of experiments was conducted which incorporated in-situ high-speed Schlieren imaging to visualize local gas flow conditions. Competition between the shield gas flow and melt pool emissions was observed which played a significant role in melt pool stability, and the role of laser beam shapes will be discussed. Overall, this insight provides a deeper understanding of beam shapes on process stability and melt pool development in DED-LB.