Part IV : Solid-Solid Phase Transformations I
Module 4 : Massive transformations
4 Massive transformations
4.1 Motivation
What is a di usionless, civilian transformation?
4.2 Massive transformation
Massive transformations are transformations in systems in which an alloy of a given composition and a particular structure (say β), changes its structure to another with the same composition (say, $^{\circ}$). An example is shown in Figure  34: in Cu-Zn system, when an alloy of 38 at.% Zn is cooled from 8500C to say 4000C at fast enough cooling rates, the structure changes from that of β to $^{\circ}$ albeit with the same composition. Since the composition is the same, there is no need for long range diffusion and hence the transformation is very fast. Such changes in structure without changes in composition can be achieved in two ways: massive which is through thermally activated jumps of atoms from regions of one phase to another (discussed in this module) and martensistic which is through diffusionless (military) (which is discussed in the next module).