phase diagrams

Question 1

COMPONENT:

Answer 1

COMPONENT: Pure Metal or Compound

Question 2

SYSTEM

Answer 2

SYSTEM: Can be ladle of molten steel, or the whole range of alloys possible

Question 3

PHASE

Answer 3

PHASE: Homogeneous part of system that has Uniform physical + chemical
characteristics (not necessarily the same compositions).

Question 4

Composition

Answer 4

Composition: concentration of each component in an alloy

Question 5

Solubility Limit

Answer 5

Maximum amount of solute that can go into solution in solvent
Max
concentration
for which only a
single phase
solution occurs.

Question 6

Effect of Temperature (T) & Composition (C)

Answer 6

Changing either or both can change # of phases

Question 7

go back and see lever rule

Question 8

if densities are the same, the volume fractions

Answer 8

• Note; if densities are the same, the volume fractions will be equal to the
  weight fractions.

Question 9

slow cooling

Answer 9

Continually changing composition during slow cooling requires Solid State
Diffusion!

Solid state diffusion : takes time and energy (temperature)
* If allow very long time for cooling then diffusion can take place

Question 10

rapid cooling

Answer 10

If cool faster, insufficient time/energy for complete diffusion
then Cored Microstructure Segregation

Question 11

at eutectic

Answer 11

Immediate freezing of liquid (like pure metal but into 2 phases rather
than one)

Question 12

At Eutectic line:

Answer 12

At Eutectic line: 3 phases in equilibrium; Liq, a, b

Question 13

Eutectic composition temperature

Answer 13

• Eutectic composition solidifies at a lower temperature than other
  compositions.

Question 14

hyper eutectic alloy

Answer 14

In a hyper eutectic alloy, the composition of the ally contains more of the alloying elements then the eutectic Composition. This means What when the alloy solidifies, the primary phase that forms first will have a composition richer the alloying elements than the eutectic composition.

b’ + (a + b)

right of the eutectic composition

Question 15

hypoeutectic alloy

Answer 15

A hypoeutectic alloys contains less of the alloying elements than the eutectic composition. this means that the primary phase that forms Ist during solidification will have a composition richer in alloying elements compared to the eutectic composition

a’ + (a + b)

left of the eutectic composition

Question 16

refer back to Micro-constituents formulasc

Question 17

compunds in phase diagrams

Answer 17

Sometimes Intermetallic Compounds are formed at particular ratios of
two metals or a metal and a non-metal.

These compounds appear as Vertical Lines on Phase Diagram

Question 18

Eutectic

Answer 18

Eutectic - liquid in equilibrium with two solids

liquid freezes to two solids

Question 19

Eutectoid

Answer 19

Eutectoid - solid phase in equilibrium with two other solid phases
S2 becomes S1+S3

Question 20

Peritectic

Answer 20

Peritectic - liquid + solid 1 à solid 2
S1 + L S2

Question 21

PEARLITE

Answer 21

(a + Fe3C)
formed by the EUTECTOID REACTION

Lamellar structure is the easiest.
* Once formed no significant changes on further cooling

Question 22

If a steel is cooled at faster rates then other things may happen:

Answer 22

phase changes may occur at different temperatures or may vary
microstructure (fine & coarse pearlite)

• may get phases at room temperature which are not on the phase
  diagram, i.e. non equilibrium phases.

Question 23

When other elements (in addition to carbon) are added to steels they
can affect the Fe-Fe3C diagram.

Answer 23

• Some move eutectoid temperature up
• Some move eutectoid temperature down
• Some move eutectoid to higher carbon concentrations
• Some move eutectoid to lower carbon concentrations