Phase Transformations and TTT Diagrams in Materials Science (Part 2: S-Curves and TTT Diagrams)

The transformation of materials into different phases is critical in mediating their properties, application and engineering performance. How do phase transformations take place? How long do they take? How can the transformation be mapped as a function of temperature and time and controlled to produce a desired microstructure?
Using examples of liquid solidification, glass formation, and transformations in Fe-C steels, in this three part tutorial you will learn about the mechanisms of phase transformations, how the nucleation and growth of a new phase depends on the degree of undercooling, and how to generate and read a so-called TTT diagram where the path of the Transformation is quantified as a function of Temperature and Time. The tutorials are presented at a level appropriate for a sophomore undergraduate introductory course in Materials Science and Engineering or related major, with some prior exposure to introductory thermodynamics.
This second video shows how the time to complete a phase transformation can be quantified at different temperatures. You will learn how to generate plots of the fraction of the phase conversion as a function of time and how these are mapped to produce a Time-Temperature-Transformation (TTT) diagram. The TTT diagrams are then used to illustrate how the cooling rate of a material can be modified to produce crystalline solids with controlled grain sizes or metallic glasses with amorphous structures.