Exam 3 Flashcards
What assumptions do we use for the growth equation of spherical solid state precipitates?
- far from the particle, a constant concentration of C∞ is maintained
- at the interface, the α phase has concentration Cα
What boundary conditions are needed for the growth equation of spherical solid state precipitates?
- C = C∞ at r=∞
2. C = Cα at r=α
What’s the concentration profile of β?
for r > α, C = (Cα - C∞)(a/r) + C∞
What’s the only impediment to uniform growth?
ΔGm
Is there a critical undercooling temperature for growth? For nucleation?
No, yes
What is constant with time for uniform growth?
The growth rate
What’s the driving force for N and U?
undercooling
What happens to protrusions during solidification into a superheated liquid?
they disappear due to planar front growth
What happens to protrusions during solification into a super cooled liquid?
they grow and may form dendrites
What is constitutional supercooling?
normal freezing with imperfect mixing of the liquid
What is the barrier to spinodal decomposition?
gradient energy
What is the barrier to spinodal decomposition?
gradient energy
