superplastic forming

Question 1

What is superplastic forming

Answer 1

a process hwere special alloys can be made to deform considerably more than conventional alloys.

• strains of up to 1000% are possible.
• enables complex shapes to be made in single step forming operation
• cost savings possible despite alloys being more expensive than conventional alloy
• process involves a combination of grain boundary sliding and diffusion

Question 2

Conditions for super plastic flow

Answer 2

1. metal must have a fine equi-axed grain structure, typically less than 5 micrometers.
2. must be deformed at temperatures above about half its absolute melting temperature in order to allow diffusion mechanisms to dominate
3. strain rate must be slow ,and the flow stress must be strain rate sensitive, so if necking starts , the strain rate in neck would increase, but flow stress would increase also and stop neck developing
4. grains must not grow during processing and must slide over each other easily. Special alloy formulations with grain grown inhibitors are required.

Question 3

What is superplasticity?

Answer 3

• used to describe materials that can be formed to high strains without formation of unstable tensile necks.
• normally applied to specific alloys but many thermoplastics also exhibit superplasticity