Lecture 11 Key notes

Phases are at equilibrium if they have te same

temperature, pressure, chemical potential

Metastable

sold phases are in contact for a long time but dont reach equilibrium (supersaturated); arent in equilibrium but chemical potential is not enough to force it

Interstitial solid solutions typically have solute solubility limits of

<10%

Substitution solid solubility limits depend on

atomic size, crystal structure, electronegativity, valence electrons

Isomorphous systems

completely soluble across all compositions NO MATTER what ratio

Liquidis Line

freezing point, liquid goes to solid, the top upper line

Solidis Line

melting point, solid to liquid, seperates Liquid from mixed solids,

Equlibrium cooling

• slow cooling that follows liquidis (top line)

• slow cooling = more time for diffusion = homogeneous crystal composition

Non equilibrium cooling

• faster cooling, not enough time for diffusion to make nice homogeneous crystal

• cored structure (rings of growth like an onion)

• segregation (different rings have different compositions of solid)

Homogenization Het treatment

hold metal just below solidious temperature (melting point) to allow for diffusion that eliminates segregation/coring problems in non-equilibrium cooling

Alloys have __________ dependent solid solution hardening

concentration; results in loss of ductility

Laminar Structure

zebra like structure

Eutectic Structure

• nucleation happens. As nucleation sites grow they bump into each other, expand, and form lines

• more nucleation = finer lines

Eutectic Point

Liquid → solid 1 + solid 2

Peritectic

Liquid + solid → solid

Eutectoid

solid 1 → solid 2 + solid 3

Peritectoid

solid 1 + solid 2 → solid 3

Phase transformation helps

Start of Word: Eu = one transforms in two things; Peri = two things converge into one

End of Word: ic = liquids, oid = solids

Intermatallic Compounds

compounds of 2 distinct metals w/ distinct chemical formula

**SOLID VERTICAL LINE on phase diagrams

Congruent Phase Transformation

no change in composition of phases involved (allotropic transformations and melting pure materials)

Incongruent Transformation

at least 1 phase changes composition (eutectic or eutectoid)

Questions → hw 8,

question 2c (actual 2c)

question 6 (Why not just alpha - co / alpha - eutectoid)

question 5 (how is it that the point is a peritectic, phase transformations just questions)

need to complete → 5 and 6