Keyhole fluctuation and pore formation mechanisms during laser powder bed fusion additive manufacturing

Keyhole porosity is a key concern in laser powder-bed fusion (LPBF), potentially impacting component fatigue life. However, some keyhole porosity formation mechanisms, e.g., keyhole fluctuation, collapse and bubble growth and shrinkage, remain unclear. Using synchrotron X-ray imaging we reveal keyhole and bubble behaviour, quantifying their formation dynamics. The findings support the hypotheses that: (i) keyhole porosity can initiate not only in unstable, but also in the transition keyhole regimes created by high laser power-velocity conditions, causing fast radial keyhole fluctuations (2.5-10 kHz); (ii) transition regime collapse tends to occur part way up the rear-wall; and (iii) immediately after keyhole…

• UD
  U.S. Department of Energy

  Awards: AC02-06CH11357, Contract No. DE-AC02-06CH11357, DE-AC02, 06CH11357, No. DE-AC02-06CH11357, DE-AC02-06CH11357, DE-AC02-
• AT
  Alan Turing Institute

  Award: EP/T001569/1
• RA
  Royal Academy of Engineering

  Award: CiET1819/10
• OO
  Office of Science

  Awards: DE-AC02-06CH11357, Contract No. DE-AC02-06CH11357, DE-AC02, No. DE-AC02-06CH11357, 06CH11357, AC02-06CH11357
• EA
  Engineering and Physical Sciences Research Council

  Awards: EP/N509577, EP/P006566/1, and EP/V061798/1, EP/W037483/1, EP/P006566, EP/V061798/1, DE-AC02-06CH11357, EP/T001569/1, EP/P006566/1, EP/R511638/1, EP/N509577/1
• OO
  Office of Naval Research

  Award: DE-AC02-06CH11357
• AN
  Argonne National Laboratory

  Awards: DE-AC02, No. DE-AC02-06CH11357, 06CH11357, AC02-06CH11357, Contract No. DE-AC02-06CH11357
• OO
  Office of Naval Research Global

  Award: N62909-19-1-2109