Iron unit cell Flashcards
Ferrite
> interstitial solid soln of C in BCC α-Fe
> a = 0.286 nm
What is γ-Fe
FCC, a = 0.365nm
What is δ-Fe
BCC, a = 0.293nm
What sites do carbon atoms occupy in ferrite? Why?
octahedral, there is less net average displacement
What is elastic strain energy equal to?
The square of the displacement of the Fe atoms
Why is solubility of C in ferrite very small?
High elastic strain energy associated with placement of carbon in octahedral sites
What is austenite?
intersitial solid solution of C in FCC γ-Fe
Why do carbon atoms occupy octahedral sites in FCC austenite?
The octahedral site voids are larger than the tetrahedral ones
The solubility of C in FCC austenite is ______ than that of C in BCC ferrite. Why?
much higher; the strain energy is substantially lower
Cementite
> intermetallic line compund
Fe3C
density is similar to ferrite
it is a metastable phase, but won’t decompose into equilibrium phases ferrite and graphite because kinetics are slow