Keyhole threshold and morphology in laser melting revealed by ultrahigh-speed x-ray imaging

By Ross W Cunningham, Cang Zhao, N. Parab, C. Kantzos, J. Pauza, K. Fezzaa, T. Sun, Anthony D. Rollett. Science, 2019

923 citations recorded by the source corpus.

The key to keyhole formation The formation of keyholes, or vapor-filled depressions, during laser welding presents a large problem for additive manufacturing. Cunningham et al. used high-speed x-ray imaging to take a detailed look at keyhole formation in a titanium alloy. They found a simplified relationship between operational parameters and keyhole shape, which may allow for the prevention of pore formation going forward. Science, this issue p. 849 Keyhole formation and morphology in a titanium alloy depend on laser power and scanning speed. We used ultrahigh-speed synchrotron x-ray imaging to quantify the phenomenon of vapor depressions (also known as keyholes) during laser melting of metals as practiced in additive manufacturing. Although expected from welding and inferred from postmortem cross sections of fusion zones, the direct visualization of the keyhole morphology and dynamics with high-energy x-rays shows that (i) keyholes are present across the range of power and scanning velocity used in laser powder bed fusion; (ii) there is a well-defined threshold from conduction mode to keyhole based on laser power density; and (iii) the transition follows the sequence of vaporization, depression of the liquid surface, instability, and then deep keyhole formation. These and other aspects provide a physical basis for three-dimensional printing in laser powder bed machines.

Subfields: Computational Mechanics, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/4f57a33005ac548c4db7d44d5999d25afd16c561

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Citations in the corpus

Additive manufacturing of steels: a review of achievements and challenges (2020, background): “Mater Sci Eng A 478(1–2):119–124 [39] Cunningham R, Zhao C, Parab N, Kantzos C, Pauza J,”
Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of Ti6Al4V: High-fidelity modelling and experimental validation (2019, background): “In another recent work, Cunningham et al. [32] captured the keyhole evolution and its porosity formation with an ultrahigh-speed X-ray imaging system for a wide range of process conditions of a titanium alloy.”
Effects of process parameters on porosity in laser powder bed fusion revealed by X-ray tomography (2019, background): “It seems higher power and speed allows a wider “safe” process parameter range with less extensive keyhole mode porosity – the higher speed suppresses instability in the vapour depression, also consistent with reports in [35].”
Mechanism of keyhole pore formation in metal additive manufacturing (2021, background): “and Cunningham et al.(20) suggested that the interaction between powder particles and laser in L-PBF only have second-order influence the keyhole fluctuation and keyhole pore formation.”
Effect of Laser-Matter Interaction on Molten Pool Flow and Keyhole Dynamics (2019, background): “In this case the absorption intensity (3.1× 1010 W/m2), surface temperature (4200 K), and recoil pressure (1×106 Pa) on the front wall are similar to those in case 1.”
Material-structure-performance integrated laser-metal additive manufacturing (2021, background): “4 MW/ cm(2)) exists from conduction mode to the keyhole regime, following the sequence of vaporization, depression of liquid surface, instability, and deep keyhole (140).”