Titanium Superplastic Forming
A hot-forming process in the fine-grain regime of titanium alloys that allows extremely large deformations without necking at low strain rates.
Superplasticity is a forming behavior that occurs in certain materials when they are slowly and uniformly stretched under defined conditions. The material then behaves almost like a viscous fluid and can be deformed extremely far without necking or cracking.
When welding, this phenomenon doesn't play a direct role for you, but you need to know about it because it affects microstructure development. If you bring titanium near such forming temperatures, you must not create rapid temperature changes or high stresses, otherwise you lose the controlled formability and get uncontrolled shape changes or cracks. So keep the heat input uniform and avoid forced constraints.