Chapter10

Chapter10 - Chapter Outline Phase Transformations Heat Treatment(time and temperature Microstructure Kinetics of phase transformations Homogeneous

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
1 MSE 2090: Introduction to Materials Science Chapter 10, Phase Transformations Heat Treatment ( time and temperature) ± Microstructure Chapter Outline: Phase Transformations ¾ Kinetics of phase transformations ¾ Homogeneous and heterogeneous nucleation ¾ Growth, rate of the phase transformation ¾ Metastable and equilibrium states ¾ Phase transformations in Fe-C alloys ¾ Isothermal Transformation Diagrams Not tested: in 10.5 Bainite, Spheroidite, Martensite… (from p. 360) 10.6 Continuous Cooling Transformation Diagrams 10.7-10.9 Mechanical behavior of Fe-C alloys, Tempered Martensite
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 MSE 2090: Introduction to Materials Science Chapter 10, Phase Transformations Phase transformations (change of the microstructure) can be divided into three categories: Phase transformations. Kinetics. ¾ Diffusion-dependent with no change in phase composition or number of phases present (e.g. melting, solidification of pure metal, allotropic transformations, recrystallization, etc.) ¾ Diffusion-dependent with changes in phase compositions and/or number of phases (e.g. eutectic or eutectoid transformations) ¾ Diffusionless phase transformation -by coop e r a t iv e small displacements of all atoms in structure, e.g. martensitic transformation (discussed in this chapter but not tested) Phase transformations do not occur instantaneously. Diffusion-dependent phase transformations can be rather slow and the final structure often depend on the rate of cooling/heating. We need to consider the time dependence or kinetics of the phase transformations.
Background image of page 2
3 MSE 2090: Introduction to Materials Science Chapter 10, Phase Transformations Phase transformations involve change in structure and (for multi-phase systems) composition ± rearrangement and redistribution of atoms via diffusion is required. The process of phase transformation involves: Kinetics of phase transformations ¾ Nucleation of the new phase(s) - formation of stable small particles (nuclei) of the new phase(s). Nuclei are often formed at grain boundaries and other defects. ¾ Growth of the new phase(s) at the expense of the original phase(s). S-shape curve : percent of material transformed vs. the logarithm of time.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 MSE 2090: Introduction to Materials Science Chapter 10, Phase Transformations Nucleation Nucleation can be Heterogeneous ± the new phase appears on the walls of the container, at impurity particles, etc. Homogeneous ±so l id nuc le i spon taneous ly appea r w i th in the undercooled phase. Let²s consider solidification of a liquid phase undercooled below the melting temperature as a simple example of a phase transformation. solid solid liquid liquid homogeneous nucleation heterogeneous nucleation supercooled liquid
Background image of page 4
5 MSE 2090: Introduction to Materials Science Chapter 10, Phase Transformations Gibbs free energy in analysis of phase transitions It is convenient to analyze phase transformations occurring under conditions of constant temperature (T) and pressure (P) by using Gibbs free energy (G) .
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/05/2012 for the course MSE 209 taught by Professor Kelly during the Spring '08 term at UVA.

Page1 / 26

Chapter10 - Chapter Outline Phase Transformations Heat Treatment(time and temperature Microstructure Kinetics of phase transformations Homogeneous

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online