Spectral Monitoring of Argon-Tungsten Arc Welding of 6-4 Titanium to Detect the Presence of Air

The need for careful shielding of the molten weld puddle from air when welding titanium is well known. Molten titanium has a very high solubility for oxygen and nitrogen, and the solution of small amounts of these gases will embrittle the titanium weld. Unfortunately, there is currently no reliable method for nondestructively determining whether oxygen or nitrogen is being picked up by the molten metal during the welding operation. In investigating the possibilities of such a system, aspects which must be evaluated include: Is the presence of nitrogen and/or oxygen detectable in the presence of a great excess of argon and other elements present--titanium, aluminum, vanadium, tungsten, plus possible impurities such as silicon, sodium, and carbon? Can such a detection system be sensitive enough to be useful? Can a rugged, sensitive and quickly responsive system be adaptable to the industrial welding environment and be economically feasible? The first two of these questions have been addressed in detail in the work reported here; the third is discussed but not fully answered.