The Effect of Reduced Pressure on Laser Keyhole Weld Porosity and Weld Geometry in Commercially Pure Titanium and Nickel

Journal Article · Tue Nov 01 00:00:00 EDT 2016 · Welding Journal

OSTI ID:1819022

Elmer, J. W. ^[1]; Vaja, J. ^[2]; Carleton, Holly D. ^[1]

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1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. AWE, Reading (United Kingdom)

Here, the beneficial effect of reduced pressure laser welding in vacuum at 10^-1 mBar was investigated in commercially pure titanium and nickel and compared to atmospheric pressure welding in Ar shielding gas. Partial penetration keyhole welds were made in these materials using a continuous wave disk laser operating at 2-4 kW and travel speeds of 12 and 17 mm/s, where moderate to severe porosity is observed under normal atmospheric pressure welding conditions. Additional welds were made in nickel using an electron beam welding process and the same parameters for comparison. Optical metallography, x-ray radiography, and computed x-ray tomography (CT) were used to characterize the porosity levels in the welds. Quantitative CT results show a monotonically decreasing pore size distribution for all of the welds, and the distributions can be fit with a 2-parameter Wiebull relationship with a beta shape factor that varied between 0.37 and 0.61 depending on the welding conditions. Other results show that laser vacuum essentially eliminates porosity in titanium, and significantly reduces porosity in nickel, but does not completely eliminate porosity in nickel. Laser vacuum welds have increased keyhole penetration and reduced weld widths compared to their atmospheric pressure counterparts, with similar beneficial geometric weld shapes as electron beam welds that are also made in vacuum. Finally, laser vacuum welds showed approximately one-half the volumetric porosity in nickel than electron beam welds, with less porosity at the weld root.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1819022
• Report Number(s): LLNL-JRNL--691153; 819224
• Journal Information: Welding Journal, Journal Name: Welding Journal Journal Issue: no. 11 Vol. vol. 95; ISSN 0043-2296
• Publisher: American Welding Society
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
computed tomography
electron beam welding
keyhole weld penetration
laser vacuum welding
porosity distribution
porosity morphology
weld geometry
weld porosity reduction