35 巻 (2017) 2 号 p. 73-84
Consumption of tungsten electrode during TIG welding process is one of unavoidable problems and many studies have been progressed to improve the consumption resistance. In general, some kinds of oxides (ThO2, La2O3, Ce2O3) are added to the tungsten electrode in order to make the thermionic emission easy and control the electrode temperature below the melting point of tungsten. However, the lifetime of electrode is still limited within a few hours because the additives evaporate and a lack of additives is caused on the electrode surface. In this study, numerical simulations which focus on the evaporation and diffusion phenomena of additives in the electrode were performed in order to clarify a consumption mechanism and identify effective factors for the lifetime of electrode.
As time passed, the mass concentration of additive decreased due to an evaporation phenomenon whereas the additive was supplied from inside to outside of electrode by a diffusion phenomenon. When the degree of coverage of additive decreased, the electrode temperature quickly increased and it reached the melting point of tungsten. The lifetime of electrode was strongly depended on the physical properties of additives such as diffusion constant and melting point of their oxides.