Kinetics and Microstructural Control

· The sequence of steps involved in going between the quenched condition and the final thermodynamic equilibrium state may be represented by the family of T-T-T diagrams shown.
· The isothermal transformation at about 150 C is long enough to complete the transformation through Guinier-Preston zones to the θ"-state and a high state of internal stress.
· Returning to room temperature stops the transformation and leaves the alloy in this metastable, high UTS state.

From: Ashby & Jones,
"Engineering Materials 2," Pergamon (1986)