Chapter 9 Flashcards
what is a phase diagram?
pictorial representations of the state of matter
solubility limit
the amount of how much solute can be dissolved in a solvent at a given temp
what conditions are pd created?
equilibrium and atmospheric, can’t always be realistically achieved
binary pd
relate phases when two elements mix
tertiary pd
relate phases when three elements mix
sign for solid
alpha
what occurs between solid and liquid of the Cu-Ni pd
two phase region, think slush
liquidus temp
above this temp, everything is liquid
solidus temp
below this temp, everything is solid
what three things do we get out of a pd?
- phases present
- phase composition
- determination of phase amounts
how to determine phase amounts of two phase region?
Inverse lever rule - the fraction of one phase is the opposite segment divided by the total length of the tie line
eutectic point
at eutectic temp and composition, a liquid transforms into 2 different solids. all three phases exist at the same time - eutectic phase
eutectic isotherm
temp of eutectic point, separates (alpha and beta) from two phase regions``
solvus line
separates (alpha) and (beta) from (alpha and beta)
alpha
solid solution, rich in element A with a little of element B, composition is different enough from the solid solution to be a separate phase
pro-eutectic
any phase forming above the eutectic isotherm - also known as primary
total isotherm
any phase forming below eutectic isotherm
eutectic phase
what forms at eutectic temp
Microstructure development
the type of microstructure that develops in the material depends on the composition of the alloy
microstructure in (L) region just more than 0%
material is liquid, with mostly A and a little bit of B
microstructure in (L + alpha) region just more than 0%
solid phase (alpha) starts to appear as temp lowers
microstructure in (alpha) region just more than 0%
material cools down and liquid disappears
what is a phase
anything that can be separated physically or chemically
what happens as a liquid cools from L > L+a > a > a+B
creates solid alpha with a little bits of solid beta. as temp decreases beta phase precipitates out
what happens as a liquid cools at eutectic composition?
in most alloys, a+B forms in a lamellar structure
what happens as a liquid cools from L > a+L > a+B
alpha will start to solidify, then as you approach
what happens as a liquid cools from L > a+L > a+B
alpha will start to solidify, then as you approach eutectic temp, alpha+beta will form lamellar structure since the last liquid to solidify has eutectic composition
what is the most commonly used metal?
iron
pure iron at room temp
BCC ferrite (alpha)
what does pure iron convert to at 912C
ferrite converts to austenite or gamma iron (FCC)
what does pure iron convert to at 1394C
austenite converts to delta ferrite (BCC)
what happens to iron at 1538C
delta ferrite melts into liquid
majority of Fe-C (steel) alloys have less than ____wt% C
6.7
cementite
present at 6.7wt% C, Fe3C, not a solid solution but an intermetallic compound
alpha ferrite - max C composition
BCC - C can go to interstitial positions so we can only dissolve0.022wt% C
gamma austenite - max C composition
FCC - spacing of lattice changes from alpha ferrite so up to 2.14wt% C
what happens above 2.14wt% C
Fe3C starts to form and remain stable
eutectic reaction of FeC
L > gamma + Fe3C
eutectoid reaction
one solid transforms into two solid phases
austenite cannot exist at ______
room temp
FeC eutectoid reaction
gamma > alpha + Fe3C
gamma > pearlite
pearlite
lamellar structure of alpha + Fe3C
hypo-eutectoid alloy cooling
starts as austenite, primary alpha starts to form along grain boundaries, then austenite becomes pearlite (alpha+Fe3C)
