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

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 vis...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2019-02, Vol.363 (6429), p.849-852
Main Authors: Cunningham, Ross, Zhao, Cang, Parab, Niranjan, Kantzos, Christopher, Pauza, Joseph, Fezzaa, Kamel, Sun, Tao, Rollett, Anthony D
Format: Article
Language:English
Subjects:
Additive manufacturing
Conduction
Keyholes
Laser beam melting
Laser beam welding
Lasers
Liquid surfaces
Manufacturing
Melting
Metals
Morphology
Pore formation
Powder
Powder beds
Rapid prototyping
Surface stability
Synchrotron radiation
Three dimensional printing
Titanium alloys
Titanium base alloys
Vaporization
Vapors
Welding
X ray imagery
X-rays
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Summary: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.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.aav4687