Welded titanium and titanium-alloy assemblies are used in airframes, jet engines and chemical equipment. These assemblies are fabricated from sheet, bar, plate and forgings, and joined by the use of inert-gas-shielded metal-arc welding, spot, seam, flash and pressure welding operations.

It has not been possible to adapt the other common welding processes such as gas welding and arc welding with active gases, coated electrodes or under fluxes to these metals, because:

(1) These metals are extremely reactive when heated to welding temperatures and readily react with air and most, elements and compounds including all known refractories.
(2) The ductility and toughness of titanium welds are reduced by the presence of small amounts of impurities, especially carbon, hydrogen, nitrogen and oxygen.

In spite of their high reactivity and low tolerance for impurities, these metals are readily adaptable to spot, seam, flash and pressure welding operations. Normal welding procedures are satisfactory with these processes. However, both tungsten-arc and consumable-electrode inert-gas-shielded metal-arc welding operations are influenced by the high reactivity of these metals and their low tolerance for impurities. Special procedures to insure against weld contamination were developed in adapting these processes to titanium assemblies. The special procedures include the use of large gas nozzles and trailing shields to shield the face of the weld from air, and backing bars that provide means for introducing inert gas to shield the back of the welds from air. Also, inert-gas-filled welding chambers are often used with these processes. In addition, dew-point measurements are made on the shielding gas to insure the use of high purity gas.

Alloy selection is important in planning welded titanium assemblies. Welded joints in some alloys have excellent mechanical properties whereas joints in other alloys are too brittle to be useful. The alpha-type alloys do not respond to heat treatment and their mechanical properties are affected only slightly by variations in microstructure. These alloys are readily adapted to all types of welding operations and are commonly used in such applications. Depending on alloy content, the mechanical properties of alpha-beta alloys may be greatly affected by heat treatments and variations in microstructure. Many of the alpha-beta-type alloys are severely embrittled by welding operations. Special consideration is required in selecting these alloys for welding applications. Only one beta alloy is presently available. Welded joints in this alloy are extremely ductile in the as-welded conditions, but their strengths are low. When heat treated to increase strength, weld ductility decreases. It has not been possible to realize the full strength potential of this alloy in welded assemblies, but recent developments are encouraging.

Although titanium and titanium alloys may be welded to themselves and each other, it is difficult to weld them to other metals. Titanium is severely embrittled by the formation of brittle intermetallic compounds, or excessive solid solution hardening when highly alloyed with most of the common structural metals. Such structures are formed when titanium is welded to other metals with processes that melt both base metals. As a result, the only reliable method for joining titanium to other metals is the use of brazing operations. However, there is a great deal of interest in the use of welding for this purpose and sufficient success has been obtained in the laboratory so that development of a method does not appear hopeless.