In a superplastic sample a grain size of $10$m must not be exceeded. Superplastic

deformation only takes place at high temperatures; therefore, grain growth will be

expected.

a$)$ What particle size is necessary to suppress grain growth $($volume fraction f $=4$

Vol$\%)?$ Assume that the radius of curvature of the grain boundaries is about $10$ times larger than the average grain size d $($ gamma$=1$ J$/$m$2).($Answer: rT $=3$m$)$

b$)$ Which conditions must the precipitates fulfil? Name another possibility to stabilise the grain size, if the usage of precipitates is not allowed.

c$)$ Name another reason why precipitates are of importance.