First Principles Total Energy Calcuations Applied to the Design of a Bulk Metallic Glass Outline: Introduction to metallic glass Computational thermodynamics “Stabilization” of glassy state Destabilization of competing phases Iron-based bulk metallic glass Current Research First principles molecular dynamics Chemical bonding Elastic moduli → ductility
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First Principles Total Energy Calcuations Applied to the Design of a Bulk Metallic Glass Outline: Introduction to metallic glass Computational thermodynamics.
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First Principles Total Energy Calcuations Applied to the Design of a Bulk Metallic Glass
Outline:Introduction to metallic glass
Computational thermodynamics
“Stabilization” of glassy stateDestabilization of competing phasesIron-based bulk metallic glass
Current ResearchFirst principles molecular dynamicsChemical bondingElastic moduli → ductility
Co-workers:
Joe Poon (University of Virginia) (DARPA-PI)Gary Shiflet (University of Virginia) Michael Gao (Virginia/CMU)
Don Nicholson (Oak Ridge National Lab)Miguel Fuentes (Oak Ridge/CMU)Marek Mihalkovic (Slovakia/CMU)Yang Wang (Pittsburgh Supercomputer Center)
Then Rapidly quench (106K/s) a thin ribbonor sputter a thin filmPure element or binary alloy
Fe-B (Honeywell/Allied Signal)
Fundamental science
Low-loss transformer cores
Now Slowly cool (1K/s) a bulk sample
Many-component alloy
Zr-Ti-Cu-Ni-Be (Cal-Tech)
Fe-B-C-Cr-Mo-Y (U. Va.)
Structural materials
Net-shape casting
Near-perfect elasticity
Golf club heads + ….
Fundamental science
Amorphous metal (metallic glass):
Bouncing Ball Demo (Liquid Metal Tech.)
Enthalpy of formationFirst-principles calculations
Known LT stable
Known HT stable
Known metastable
Unknown/hypothetical
First-Principles Thermodynamics
Use program VASP with PAW potentials, GGAFully relax all structures to optimal configurationsSubtract from tie-line to obtain enthalpy of formation (T=0K)Apply statistical mechanics to incorporate temperature
Strategies for reaching finite temperature:Alloy Theoretic Automated Toolkit (Axel van de Walle, CalTech)
fitfc determines vibrational free energy in quasiharmonic approximationmaps/emc2 determines free energy of chemical substitution
CALculation of PHAse Diagrams (e.g. ThermoCalc®)Develop database of thermodynamic dataImprove and constrain database using first-principles data
Cohesive energy database (http://alloy.phys.cmu.edu)Enthalpies of ~ 2500 structures in 200 binary and 100 ternary+ systems
Computational Thermodynamics:First-principles calculations valuable source of T=0K enthalpiesResearch needed on finite temperature methods
Stat. Mech. (ATAT)/Thermodynamics (CALPHAD)Applicable to many problems in materials designPredicted role of large atoms in metallic glass stabilization
Amorphous metal structure and bonding:MD can achieve liquid and supercooled liquid structureCan classify bonding according to ionicity and covalencyHow to use this information to improve ductility?