A study has been made of the effect of nitrogen and hydrogen in the arc atmosphere of blowhole formation in tungsten inert gas arc welding of nickel. The blowhole in specimen was detected by means of radiographical and cross-sectional methods. The results are summerized as follows:
1) Ni-H₂O system; Pure nickel plates were welded in various water vapor contents of argon shielding gas. Any blowholes were not produced in the solidified specimens.
2) Ni-H system; It was found that the critical hydrogen concentrations of the atmospheres (Ar-H₂) forming blowhole in solidified nickel are 50 % hydrogen for TIG welding method and 18 % hydrogen for leviation melting method (non-arc melting). It was only observed in the arc welding that the generation of fine nickel particles (vapor-like) from the melt increases with increasing the hydrogen concentration in the arc atmosphere, especially, this generation becomes more remarkable above 20 % hydrogen
3) Ni-N system; Blowholes by nitrogen were easily formed in this system as far as an arc was used. The critical nitrogen concentration of the atmosphere on blowhole formation of nickel by TIG welding was found to be 0.025 % nitrogen. On the other hand, any blowholes by nitrogen were not produced in nickel specimens which were melted under a 100 % nitrogen atmosphere by levitation melting method (non-arc melting). The difference of blowhole formation between arc welding and non-arc melting can be explained by the difference of nitrogen absorption mechanism into the molten nickel.
4) Ni-H-N system; The blowhole formation of this system was mainly dominated by nitrogen concentration in the arc atmosphere (N₂-H₂-Ar), however, hydrogen in the arc atmosphere had effects on .the shape of blowhole and the nitrogen content of welded nickel.