Titanium Welding

Welding titanium is widely used in many application, example popellant motor case, high pressure storage vessel, jet engine components and steam turbine condensor. Being a reactive metal will react with oxygen, nitrogen, hydrogen, carbon and most refractories and metal.

In general, welding of titanium and its alloys can be readily performed, but it is necessary to exclude reactive gases, including oxygen and nitrogen from the air, and to maintain cleanliness. Thus weld properties are heavily influenced by welding procedures, especially by the adequacy of inert gas shielding.

The GTAW (gas tungsten arc welding) process is common, although GMAW (gas metal arc welding), friction welding, laser welding, resistance welding, plasma arc welding, electron beam welding, and diffusion bonding are all used in some cases. Both alloy composition and microstructure are important in determining weldability, with the presence of beta phase having a deleterious effect.

Unalloyed titanium and alpha alloys are generally weldable and welded joints generally have acceptable strength and ductility. Postweld stress-relief annealing of weldments is recommended. Some alpha-beta alloys, specifically Ti-6Al-4V, are weldable in the annealed condition as well as in the solution treated and partially aged condition (aging can be completed during the post-weld heat treatment). Strongly stabilized alpha-beta alloys can be embrittled by welding, the result of phase transformations occurring in the weld metal or the heat affected zone. Some beta alloys are weldable in the annealed or the solution treated condition.

Welding Environment

Most titanium welding today is done in the open fabrication shop, although chamber welding is still practiced on a limited basis. Field welding is common. Wherever the welding is done, a clean environment is necessary in which to weld titanium. A separate area, specifically set aside for the welding of titanium, aids in making quality welds. This area should be kept clean and should be isolated from dirt-producing operations such as grinding, torch cutting and painting. In addition, the welding area should be free of air drafts and humidity should be controlled.

Welding Processes

Titanium and its alloys are most often welded with the gas tungsten-arc (GTA or TIG) and gas metal-arc (GMA or MIG) welding processes. Resistance, plasma arc, electron beam and friction welding are also used on titanium to a limited extent. All of these processes offer advantages for specific situations. However, the following discussion will be concerned primarily with GTA and GMA welding. Many of the principles discussed are applicable to all processes.
Gas Tungsten-Arc (GTA) and Gas Metal-Arc (GMA) Welding

The GTA process can be used to make butt joints without filler metal in titanium base sheet of up to about 1/8-inch thickness. Heavier sections generally require the use of filler metal and grooved joints. Either the GTA or GMA welding process can be used, although GMA welding is more economical for sections heavier than about one-half inch. If the GTA process is used, care should be exercised to prevent contact of the tungsten electrode with the molten puddle, thereby preventing tungsten pickup.