Effect of Welding Atomosphere on Commercial Pure Titanium Welds

Abstract

Mechanical properties were investigated of welded joints of commercial pure titanium sheets of 1 and 2 mm thickness, which were welded by TIG in a controlled atmosphere welding chamber filled with either pure or impure argon mixed with an impurity gas of air, nitrogen, oxygen or hydrogen. Moreover, comparison of mechanical properties of TIG welds in pure argon welding atmosphere (760 mmHg) with electron-beam welds in high vacuum was done.
The conclusions are as follows:
(1) Quantity of N₂ and O₂ gases in weld metal increased proportionally with an increase of air partial pressure in argon welding atmosphere.
(2) Air gas more than 10³ to 1.4×10³ ppm(vol.) in pure argon atmosphere increased the hardness, and embrittled the mechanical properties of weld metal.
(3) Among the three elementary gases of N₂, O₂ and H₂, N₂ gas had the most detrimental effect on weld metal.
However, H2 did not change the hardness and tensile strength, although it embrittled the weld metal when it exceeded 10⁴ ppm.
(4) Embrittleness at room temperature in mechanical properties, especially in reduction of area and elongation, of contaminated weld metal which was welded in impure argon was not observed at temperatures over about 300°C.
(5) Estimation of other mechanical properties and quantity of gases in weld metal is possible by measuring only the hardness in the weld metal (shown in Fig. 24).
(6) The weld metal welded in pure argon was the most hardened and strongest zone in a welded joint, and therefore tensile fracture of a welded joint occurred in base metal.
(7) Rupture at 1000 hr. of weld and base metal at 400°C were about 9.5 kg/mm².
(8) Impact strength of the electron-beam weld of a 6 mm thick plate was about 30% greater than the TIG weld obtained in a pure argon atmosphere (760 mmHg).