MME 340 PHASE TRANSFORMATIONS IN MATERIALS

1. MME 340 PHASE TRANSFORMATIONS IN MATERIALS ANANDH SUBRAMANIAM Materials Science and Engineering INDIAN INSTITUTE OF TECHNOLOGY KANPUR New Delhi- 110016 Ph: (+91) (512) 259 7215, Fax: (+91) (512) 259 7505 anandh@iitk.ac.in http://home.iitk.ac.in/~anandh/

2. UNIVERSE STRONG WEAK ELECTROMAGNETIC GRAVITY HYPERBOLIC EUCLIDEAN SPHERICAL ENERGY SPACE nD + t FIELDS PARTICLES METAL SEMI-METAL SEMI-CONDUCTOR INSULATOR NON-ATOMIC ATOMIC BAND STRUCTURE STATE / VISCOSITY LIQUID CRYSTALS GAS SOLID LIQUID STRUCTURE CRYSTALS RATIONAL APPROXIMANTS QUASICRYSTALS AMORPHOUS SIZE NANO-QUASICRYSTALS NANOCRYSTALS

3. Casting • Metal Forming • Welding • Powder Processing • Machining Thermo-mechanical Treatments Crystal Atom Structure Microstructure Component Electro- magnetic Phases + Defects • Vacancies • Dislocations • Twins • Stacking Faults • Grain Boundaries • Voids • Cracks Residual Stress + Processing determines shape and microstructure of a component

4. Transformations in Materials Phases Defects Residual stress Defect structures can change Stress state can be altered Phases can transform Phase transformation Defect structuretransformation Stress-statetransformation Geometrical Physical Structural Property Phases Microstructure Phases Transformations Microstructural Transformations

5. Phase Defined Using GEOMETRICAL Entities PHYSICAL Properties E.g. Spin, Magnetic Moment E.g. Atoms, Cluster of AtomsIons, etc. ORDER ORIENTATIONAL PROBABILISTIC OCCUPATION POSITIONAL

6. Thermal • Magnetic • Ferroelectric Physical Property Sources of Residual Stress Geometrical Phase transformations & reactions The product of phase transformation or reaction would have a different morphology as compared to the parent phase Structural • Volume, Shape change • Coherent/semi-coherent precipitates • Epitaxial structures (coherent/semi-coherent) Defects • Vacancies • Dislocations • Twins • Stacking Faults • Grain Boundaries • Voids • Cracks

7. Geometric structure Thermal Sources of Residual Stress Physical property • Thermal • Magnetic • Ferroelectric Structural Phase transformations & reactions • Coherent/semi-coherent precipitates • Epitaxial structures (coherent/semi-coherent) Defects • Vacancies • Dislocations • Twins • Stacking Faults • Grain Boundaries • Voids • Cracks

8. Phase Transition Transitions between two phases of identical chemical composition Phase Transformation Covers a wider spectrum of phenomena Includes PHASE REACTIONS leading to compositional changes E.g.: ’ →  +  (different crystal structure & chemical composition)  →  +  Note: Identical chemical composition  equilibrium point defect concentration may be different in the polymorphs (but considered to be of identical composition)

9. Some Questions? What is a Phase? What kind of phases exist? What constitutes a transformation? How can we cause a phase transformation to occur?  The stimuli: P, T, Magnetic field, Electric field What kind of phase transformations are there? Why does a phase transformation occur?  Energy considerations of the system? Thermodynamic potentials (G, A…)

10. Length Scales Involved Nucleus Atom Crystal Microstructure Component Defects