Lanthanum Tungsten Electrode Analysis

Lanthanum tungsten electrode is mainly produced by powder metallurgy method. It is added 1%, 1.5% or 2% lanthanum oxide to tungsten powder, after doping, reduction, vertical melt, swaging and stretching to obtain lanthanum tungsten electrode. Lanthanum tungsten electrodes have good welding performance, long service life, and no radioactive contamination, so it is considered the best substitute for thorium tungsten electrode and it is widely used in tungsten inert gas welding (TIG welding), plasma welding and cutting field. By comparison electrical property found, lanthanum tungsten electrode’s electrical property is superior to cerium tungsten electrode and thoriated tungsten electrode. Lanthanum oxide, having low mobility and evaporation rate, can form a good lap dovetail organization, so lanthanum tungsten electrode has good high temperature creep performance.

After swaging process, La₂O₃ particle is evenly distributed over the tungsten grain and boundaries. If not properly control billet processing, it is prone to delamination or peeling. On the other hand, if feeding too fast in swaging process can also cause delamination or peeling.

After electrical property analysis understand the La and Ce distribution in lanthanum tungsten electrode and cerium tungsten electrode. At DC 200A, for 20min, the electrode tip working at high temperature 2600 ~ 3000 ℃, La₂O₃ and Ce₂O₃ from the center migrate to the surface and to the tip. Their average content decreased gradually from the edge to the center portion and there has almost no La₂O₃ andCe₂O₃. Ce₂O₃ has faster migration and evaporation rate.

After electrical property test observed electrode’s microstructure found that the electrode grains grow along axial direction. The grains aspect ratio of cerium tungsten electrodes and lanthanum tungsten electrode is respectively (3: 1 to 15: 1), (3: 1 to 7: 1). In lanthanum tungsten electrode there are a large number of bubbles and a small amount of La₂O₃ particle. Besides, grain boundaries are dovetail lap organizations which can impede grain boundary sliding laterally, so it has better thermal shock, creep performance. Lanthanum tungsten electrode electrical property is better than other electrodes.

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