Chapter 9 (Phase diagrams)
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What are the components?
the elements or compounds which are mixed initially
what are the phases?
the physically and chemically distinct material regions
what is the solubility limit?
maximum amount of solute that can go into solution in solvent. Also the maximum concentration for which a single phase can occur
what happens after the solubility limit is exceeded?
we have now created a 2 phase mixture
what is equilibrium
the state of lowest free energy, also the most stable one
what is particular about equilibrium phase diagrams
there are no rapid changes in state
what is a binary alloy?
a mixture of 2 metals
what is a ternary alloy?
a mixture of 3 metals
what characteristics should 2 metals have to become an alloy? (4)
• Both FCC • similar size • similar valence • they should be good solubility
how do we determine the composition of a mixture of phases from a phase diagram?
from the point we draw a line across to each phse a down from those points to the x-axis, those values will give us the respective compositions
describe how to use the tie line?
the numerator will always be the distance AWAY from the phase youre trying to determine
what is the liquidus line
the line ABOVE which ONLY LIQUID is present
what is the solidus line
the line BELOW which ONLY SOLID is present
what can be said about solid state diffusion
takes more time and temperature
what can be said about the grain structure during equilibrium cooling
the grains would be uniform
what would happen if the material was cooled very quickly?
the final grain composition would not be uniform, aka “CORED” grains
what are cored grains
when we cool a materials very quickly, the inner layer has a different composition from the outer layer
what is a eutectic reaction?
when a liquid is transformed into 2 different solid phases
how many phases are there at the eutectic line?
3
how are fixed compositions represented?
by vertical lines on phase diagrams
what is eutectic?
a liquid in equilibrium with two solids (L alpha + Beta)
what is eutectoid
solid phase in equilibrium with 2 other solids phases a –» Beta+gamma
what is peritectic
liquid+solid 1 —> solid 2
in the Iron carbon system what is alpha?
ferrite. an interstitial solid solution of carbon in BCC iron