mme 340 phase transformations in materials anandh subramaniam materials science and engineering...
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MME 340MME 340PHASE TRANSFORMATIONS PHASE TRANSFORMATIONS
IN MATERIALSIN 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
http://home.iitk.ac.in/~anandh/
UNIVERSE
PARTICLES
ENERGYSPACE
FIELDS
STRONG WEAKELECTROMAGNETICGRAVITY
METALSEMI-METAL
SEMI-CONDUCTORINSULATOR
nD + t
HYPERBOLICEUCLIDEANSPHERICAL
GAS
BAND STRUCTURE
AMORPHOUS
ATOMIC NON-ATOMIC
STATE / VISCOSITY
SOLID LIQUIDLIQUID
CRYSTALS
QUASICRYSTALS CRYSTALSRATIONAL APPROXIMANTS
STRUCTURE
NANO-QUASICRYSTALS NANOCRYSTALS
SIZE
Atom Structure
Crystal
Electro-magnetic
Microstructure Component
Thermo-mechanical Treatments
Phases Defects+
• Casting• Metal Forming• Welding• Powder Processing• Machining
• Vacancies• Dislocations• Twins• Stacking Faults• Grain Boundaries• Voids• Cracks
+ResidualStress
Processing determines shape and microstructure of a component
Phases Defects Residual stress
Transformations in Materials
Defect structures can changePhases can transform Stress state can be altered
Phase transformation
Defect structuretransformation
Stress-statetransformation
Geometrical Physical
MicrostructureMicrostructurePhasesPhases
Microstructural TransformationsMicrostructural TransformationsPhases TransformationsPhases Transformations
Structural Property
Phase Defined Using
GEOMETRICAL Entities PHYSICAL Properties
E.g. Atoms, Cluster of AtomsIons, etc.
E.g. Spin, Magnetic Moment
ORDER
ORIENTATIONAL POSITIONALPROBABILISTIC 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?
Nucleus Atom Crystal Microstructure Component
Defects
Length Scales Involved