Ch 8 Flashcards
Define equilibrium
Changes are carried out slowly enough that the phases in the system have the same properties everywhere and there are no concentration gradients
Is diffusion faster, slow in solids
Slow
Define phase
A region of matter which has homogeneous physical and chemical properties
Define phase diagram
A graphical representation (map) of the phases present with variations in temperature in composition, when thermodynamic equilibrium has been achieved
Define polyphase materials
Materials containing two or more coexisting phases
4 things that the properties of polyphase materials depend on
Define components
The elements (atoms), molecules, or compounds, which are initially mixed
Define solute
Present in minor concentration
Define solvent
Present in major concentration
Define solubility limits
The max concentration of solute that may be added, without forming a new phase
Define metastable
Nonequilibrium state, which may persist for a very long time
Are metastable phases, shown on phase diagrams
How can they be formed?
No
Can be formed due to rapid cooling
Define isomorphous
Having the same structure
What does isomorphous mean in terms of phase diagrams?
Isomorphicity is having the same crystal structure in the solid phase and complete solid solubility for all compositions
Binary phase diagrams: what happens when a mixture exhibit clustering in the solid
A miscibility gap
What does a binary phase diagram show?
The phases present at equilibrium of two different elements
Describe the binary phase diagram
(Where liquid and solids are and the liquidus line and solidus line)
Define solidus line
(2 definitions)
Line on the phase diagram, where solidification is complete upon equilibrium cooling
Where melting begins upon heating
In heating what’s line must you stay below?
Solidus line
Or it will lose its shape by partial melting
Define liquidus line
(2 definitions)
Line on a phase diagram above, which melting of a solid is complete upon heating
Where solidification begins upon cooling
In melting an alloy what do you need to do if you want a homogeneous liquid
Must exceed the liquidus line
Define system composition/overall composition
How much of each element is present in total?
What variable represents system composition?
Define Tieline
A horizontal line constructed across a two phase region of binary phase diagrams 
What does the tie line intersect on either end?
The phase boundaries that represent the equilibrium composition at the given temperature in the question
Steels: what are the two Greek letter symbols for the solid phases
Define phase constitution
(3 things)
The number and types of phase is present
The composition of each phase
The amount of each phase
Describe the three things you get from a tie line

What does the evolution of the microstructure depend on?
How rapidly the system is cooled
Can you see microstructure under a microscope?
Yes
Three things that micro structure includes
Phase constitution
Morphology and spatial distribution of phases
What does the evolution of the microstructure depend on?
How rapidly the system has cooled from high temperature
Phase diagrams: as a liquid solution is cooled it will start solidifying at what line
Liquidus line
Phase diagrams: what leads to concentration gradients in grains
The change in concentration with decreasing temperature if cooling is rapid
Phase diagrams: what happens if we cool slowly enough
The grains at formal experience diffusion in the concentration gradient, due to compositional changes during cooling will be illuminated
Phase diagrams: at true equilibrium what can be said about the composition and structure of each phase
They are spatially uniform
Phase diagrams: why is the composition of the solid and liquid phase is changing as a system is cooled
Because the liquidus and solidus lines have a slope to them
Define eutectic
Easily melted
Eutectic phase diagrams: define invariant point
Where there is an equilibrium between the two phase solid region, and a liquid
Eutectic phase diagrams: what happens upon heating?
Liquid starts to format the eutectic temperature
What variable represents eutectic temperature?
What type of phase diagram is this?
Binary eutectic phase diagram
Label the six different lines
What do the blue arrow show?
The max solid solubility for the single phase solids
These compositions are the endpoints of the eutectic isotherm
What is the most common eutectic structure?
Lamellar eutectic
What are the hypo and hyper eutectic compositions based on?
(Binary eutectic, phase diagrams)
Based on the component on the left side, being the solvent in the component on the right side, being the solute
Define hypo, eutectic composition
Are the range of compositions above the solubility limit of being a at the eutectic temperature up to, but less than the eutectic composition
In terms of hypo and hyper, which one means less, and which one means more
Hypo equals less
Hyper equals more
Define hypereutectic composition
The range of compositions above the eutectic composition up to the solid solubility limit of ANB at the eutectic temperature
Define the pro eutectic phase
The first phase to start solidifying from the liquid upon cooling for a hypo or hyper eutectic overall composition
What is the notation for pro eutectic?
(And other name)
Primary phase
At what temperature does the protective phase form?
Add temperatures above the eutectic temperature, but below the liquidus
Binary, eutectic diagram: where is the
hypo eutectic
Eutectic
Hypereutectic
A eutectoid reaction is similar to a eutectic reaction, except for what
The high temperature liquid phase replaced by another solid phase so that the whole reaction is in solid state
Define eutectoid reaction
Upon cooling one solid phase, transforms, isothermal, he and reversibly into two new solid faces that are intimately mixed
Define eutectic reaction
Upon cooling a liquid phase transforms, isothermal, he and reversibly into two intimately mixed solid faces
Defined the proeutectoid phase (primary phase)
A solid that starts to nuclear at a service line rather than at the liquidus line
