MME 340 PHASE TRANSFORMATIONS IN MATERIALS ANANDH SUBRAMANIAM Materials Science and Engineering INDIAN INSTITUTE OF TECHNOLOGY KANPUR New Delhi Ph: (+91) (512) , Fax: (+91) (512)

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

AtomStructure Crystal Electro- magnetic MicrostructureComponent Thermo-mechanical Treatments PhasesDefects+ Casting Metal Forming Welding Powder Processing Machining Vacancies Dislocations Twins Stacking Faults Grain Boundaries Voids Cracks + Residual Stress Processing determines shape and microstructure of a component

PhasesDefectsResidual stress Transformations in Materials Defect structures can change Phases can transform Stress state can be altered Phase transformation Defect structure transformation Stress-state transformation GeometricalPhysical Microstructure Phases Microstructural Transformations Phases Transformations StructuralProperty

Phase Defined Using GEOMETRICAL EntitiesPHYSICAL Properties E.g. Atoms, Cluster of Atoms Ions, etc. E.g. Spin, Magnetic Moment ORDER ORIENTATIONALPOSITIONALPROBABILISTIC OCCUPATION

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

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

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

 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…) Some Questions?

NucleusAtomCrystalMicrostructureComponent Defects Length Scales Involved