Superplastic forming is a process wherby certain materials can be uniformly deformed by great amounts. In some cses this can be by more than 1000%. This behaviour is known as Superplasticity
For a material to show this Superplastic behaviour, it will normally show the following properties:-
1) The grain size must be fine. Usually grain diameters wil be less than 5 microns.
2) The alloy must be deformed at a high temperature, usually, this is between 0.5-0.7 of the Melting Point of the material.
3) A very slow strain rate is usually employed.
4) The stress required to deform the alloy must be sensitive to the strain rate, this is to prevent Necking.
5) The grain boundaries need to allow the grains to flow over each other.
Superplastic forming is important in Beta Titanium Alloys, especially in Ti6Al-4V, where is can be coupled with Diffusion bonding to allow the fabrication of such items as Satellite fuel tanks.