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3.40 Physical Metallurgy Lecture #5 Review Metallic Bonding

3.40 Physical Metallurgy Lecture #5 Review Metallic Bonding. Presented by Leon Faison Course 2N. Agenda. Metallic Bonding Indicative Properties Metastability Research Work Embedded Atom Method. Metallic Bonding. Indicative Properties Shiny Malleable

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3.40 Physical Metallurgy Lecture #5 Review Metallic Bonding

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  1. 3.40 Physical MetallurgyLecture #5 ReviewMetallic Bonding Presented by Leon Faison Course 2N

  2. Agenda • Metallic Bonding • Indicative Properties • Metastability • Research Work • Embedded Atom Method

  3. Metallic Bonding Indicative Properties • Shiny • Malleable • High electrical and thermal conductivity can be contributed to the delocalized, free electrons in the atoms No Gap

  4. Metallic Bonding Metastability • Shiny solids on Earth is a miracle except for gold (most noble) • Standard Gibbs free energy of the formation of Fe2O3 reveals that there are -3.8 eV per Fe atom!

  5. Metallic Bonding H (thickness) Metastability • Parabolic Kinetics acts as the defense mechanism for metals from further oxidation • It does not always work, for example, localized pitting corrosion • Combination of chemical and mechanical attack can manifest in the metal’s passivation layer time H oxygen oxidized, “passivation” layer metal

  6. Metallic Bonding U.S. Navy warships are vulnerable to this “joint attack” of chemical and mechanical manifestations Superstructures are made from aluminum (5456-H116) and exposed to the marine environment

  7. Metallic Bonding • Alloying elements of the 5456-H116 such as Magnesium precipitate toward the grain boundaries • High elevated temperatures accelerate the onset of “sensitization” • Due to the potential difference between Aluminum and Magnesium, a galvanic cell is created by the presence of salt water in the marine environment • Cracks begin to form on the deck plating and others areas of the superstructure (e.g. high stress areas).

  8. Metallic Bonding Possible Solutions • Weld repairs worsen already affected aluminum • GMAW/P - Pulsed Gas Metal Arc Welding • Rapidly switches the welding output from high peak current to low background current

  9. Metallic Bonding Embedded Atom Model • The free electrons are shared between all atoms and do not “belong” to a particular ion (Communism!) • Like glue, this sea of electrons provides bonding energy which is less than individual isolated atomic states

  10. Metallic Bonding Embedded Atom Model (Mathmatically) e.g. Note Must also consider bond angle dependence when dealing with electron gas/electron liquid in a 3-atom quantity where it is shown that metallic bonding tends to be more isotropic than covalent. j ρ(rij) j ρ(rij) Xi ρ(rij) ρ(rij) = glue projection function j

  11. Metallic Bonding Embedded Atom Model Applications • Energy potential over lattices sites to compare the stability of different crystal structures at zero pressure 2. Molecular dynamics for non-perfectly arranged atoms (ma = F) eb Ω

  12. Questions?

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