Chapter 9 - Phase Diagrams Flashcards
What is a component?
Any metal that is part of an alloy
What is a system?
Either a specific alloy or series of alloys
What is a solubility limit?
The maximum concentration of solutes that may dissolve in a solvent to form a solid solution
What is a phase?
A homogenous portion of a system that has uniform physical and chemical characteristics
What is free energy?
A function of a systems internal energy and entropy
When is a system at equilibrium?
The free energy is at a minimum
What is phase equilibrium?
When an equilibrium is referred to in a multiphase system
What is a non-equilibrium state?
Equilibrium is not approached due to the rate of approaching equilibrium being very slow
What is a phase/equilibrium diagram?
Depicts the different phases a system can have, separated by lines
What is a binary phase diagram?
Depicts the phases of a two component system at various temperatures and compositions
What type of system is the copper-nickel system?
Binary Isomorphous
What is an isomorphous system?
There is complete liquid and solid solubility
What phases are included in binary isomorphous systems?
Alpha (a), Liquid (L), and both (a + L)
What information does a phase diagram provide?
The phases, compositions at said phases, and the percentages of said phases
What is the solidus line?
Separates the solid/liquid phase from the pure liquid phase
What is the liquidus line?
Separates the L and a + L phases
How is a composition determined when the point chosen lies in a two phase region?
By using a tie line and then using linear interpolation
WL = (Ca - C0)/(Ca - CL)
Wa = (C0 - CL)/(Ca - CL)
Ca = concentration of alpha phase at tie line
CL = concentration of liquid phase at tie line
C0 = concentration of component at point
W = weight fraction
What happens to the microstructure at an equilibrium cooling?
The change in temperature is extremely slow, so the phase change occurs smoothly
What happens to the microstructure at a non-equilibrium cooling?
Compositional readjustments are necessary
What is a binary eutectic phase diagram?
Contains 3 pure phases, a, B, and L, and mixed phases, a + L, a + B, B + L
What is the solvus line?
The line that separates a pure solid phase from the mixed solid phase (a + B)
What is a eutectic reaction?
The reaction occurs at point where the metal is easily melted
What is the eutectic point?
The point where the liquidus lines for both pure metals meet on the eutectic isotherm
How is a eutectic reaction defined?
L(CE) = a(CaE) + B(CBE)
What is the difference between eutectic and primary a’s or B’s
Primaries are formed before crossing the eutectic isotherm
What is the eutectic isotherm?
The horizontal line separating the a + B phase from the phases that include L
What is a terminal solid solution?
A solution with only solid phases, found at the extremes
What is an intermediate solid solution?
Solid solutions found at spots other than the composition extremes
Not at 100% of each metal in the alloy
What is a eutectoid reaction?
Consisting of 3 solid phases, delta (d) = gamma (y) + epsilon (e)
What is a peritectic reaction?
d + L = e
What does Gibbs’ Phase Rule describe?
It describes the number of phases present within a system in terms of the number of external variables, components, and non-compositional variables
P + F = C + N
What are some intermediate phases of the iron-carbon alloy?
Iron carbide (cementite), gamma-iron (austentite), delta ferrite, alpha ferrite, pearlite,
Which phase is the eutectic structure?
a + B
