Welding of titanium alloys: fatigue and residual stresses

Titanium alloys are very suited for highly specialized applications such as naval constructions where resistance to corrosion is the most important issue to be considered in materials selection, aerospace structures where the primary goal is to achieve high specific strength, and orthopedic prosthetic treatments where biocompatibility between implants and human tissues is mandatory. Welding of titanium alloys is still considered a fairly uncommon process because industrial applications of these materials cover only the above mentioned niches where the unique properties of titanium and its alloys represent the best option in terms of minimizing the lifetime cost of the structure yet meeting stringent requirements on structural integrity and safety. However, whilst high quality welded components without inclusions and distortions and with a mild notch at the weld toe can be obtained through appropriate selection of welding process parameters, it should be considered that the weld cord is anyhow a geometric discontinuity in the structure, which modifies stress distribution. Furthermore, residual stresses are an unavoidable consequence of the thermal welding cycle.