Critical instability at moving keyhole tip generates porosity in laser melting

Laser powder bed fusion is a dominant metal 3D printing technology. However, porosity defects remain a challenge for fatigue-sensitive applications. Some porosity is associated with deep and narrow vapor depressions called keyholes, which occur under high-power, low-scan speed laser melting conditions. High-speed x-ray imaging enables operando observation of the detailed formation process of pores in Ti-6Al-4V caused by a critical instability at the keyhole tip. We found that the boundary of the keyhole porosity regime in power-velocity space is sharp and smooth, varying only slightly between the bare plate and powder bed. The critical keyhole instability generates acoustic waves in the melt pool that provide…

• NS
  National Science Foundation

  Award: 1752218
• UD
  U.S. Department of Defense

  Award: ST1605-17-02
• UD
  U.S. Department of Energy
• UO
  University of Virginia
• TU
  Tsinghua University