GAS TUNGSTEN ARC is the most extensively used welding process for joining refractory and reactive metals. Refractory metals (notably tungsten, molybdenum, tantalum, niobium, and chromium) have extremely high melting temperatures and, like the reactive metals (such as titanium alloys, zirconium alloys, and hafnium), are readily oxidized at elevated temperatures unless protected by an inert gas cover. Absorption of impurities such as oxygen, nitrogen, hydrogen, and carbon will decrease toughness and ductility of the weld metal,