Pore evolution mechanisms during directed energy deposition additive manufacturing

Area of Science:

• Materials Science
• Additive Manufacturing
• Computational Modeling

Background:

• Porosity in directed energy deposition (DED) significantly degrades component mechanical properties, hindering its use in critical applications.
• The precise mechanisms of pore formation and evolution within the DED process remain incompletely understood.

Purpose of the Study:

• To elucidate the fundamental mechanisms governing pore formation, migration, growth, and entrapment during the DED process.
• To provide insights for developing effective strategies to minimize porosity in DED components.

Main Methods:

• In situ X-ray imaging was employed to observe pore dynamics in real-time during DED.
• Multi-physics computational modeling was utilized to simulate and analyze pore evolution mechanisms.

Main Results:

• Five distinct mechanisms contributing to pore evolution were identified and quantified: bubble entry and migration, bubble escape/coalescence/entrapment, bubble pushing by solidification fronts, Marangoni flow effects on bubble stability, and bubble escape or entrapment based on size.
• Bubble migration patterns (circular or lateral) and the influence of Marangoni flow on bubble behavior were detailed.
• The critical size for bubble escape versus entrapment was investigated.

Conclusions:

• The identified pore evolution mechanisms provide a comprehensive understanding of defect formation in DED.
• These findings offer a scientific basis for designing DED process parameters and material compositions to reduce porosity.
• Minimizing porosity through understanding these mechanisms is crucial for enhancing the reliability and safety of DED-manufactured parts.