Superplasticity
Superplasticity is the property of a polycrystalline material to deform plastically super under certain conditions. During superplastic deformation (English Superplastic forming SPF), the material to several 100 % stretch without constricting or breaking. Some alloys reach breaking elongations greater than 1000%.
Typical superplastic alloys have grain sizes below about 10 microns, require a forming temperature of 0.5 Tm ( Schmelztemp. in K) and low strain rates (~ 5% / min = 0.0008 / s).
Examples of superplastic alloys are:
- Ti6Al5V ( obtained at 850 .. 525 ° C and 5 % / min strain at break of > 700% )
- AlZnMg, AlCuZr, AlLiZr ( reached at 490 .. 540 ° C elongation of up to 1200 %)
A similar behavior of plastics is not referred to as super plasticity, as they are non-crystalline property and is not due to grain boundary effects.