Class 5
Phase Diagrams Continued
Copper Zinc Phase Diagram
1085C
420C
Peritectic reaction Liquid + solid 1 -> solid 2.
Eutectoid reaction Solid 1 -> solid 2 + solid 3
Maximum solid solubilty of zinc in copper is 38% at around 450C
Substitutional Solid Solubilty
How much one element will dissolve in another is determined by the Hume Rothery rules
1.
Atomic radii should be within 15% of each other
2
Crystal structure should be the same for each element for good solubility
3
Electronegativities should be similar.
4
The valences of the atoms should be similar.
Good solubility Cu –Ni, Cu-Au; Cu r=0.128A, Ni r=0.125, Au r=0.144
Crystal structure Ti- HCP, Al - FCC
Poor soluility Na-Cl Na electronegativity 0.9, Cl 3.0
Valences – Zn 2+, Cu 1+
Only indicate solubility from these rules.
DOES NOT APPLY TO THE ELEMENTS H,C,O,N,B THESE FORM INTERSTITIAL
SOLID SOLUTIONS.
Iron Carbon Phase Diagram
1538C
Liquid
3367 SUBLIMES
Fe - a then  then d
912C 1394C
Steels
Eutectoid
S1 -> S2 + S3
-> a + F e3C
Peritectic
S1+L -> S2
d + L -> 
 +L
Fe3C- cementite
A compound
 + Fe3C
a + Fe3C
Stainless Steel Phase Diagram
Ternary phase diagram for stainless steels. In this case an isothermal section at a constant
temperature is used.
Lever Arm Rule
Determine the AMOUNTS of each phase use the Inverse Lever Arm Rule.
Amount of solid = wa-wl/ws-wl
Amount of liquid = ws-wa/ws-wl
Amount of solid at 1300C is therefore 53-45 / 58-45 = 8/13 = 0.615= 61.5%
Amount of liquid at 1300C is therefore 58-53 / 58-45 = 5/13 = 0.385 = 38.5%
Change Average Composition 50%
Determine the AMOUNTS of each phase use the Inverse Lever Arm Rule.
Amount of solid = wa-wl/ws-wl
Amount of liquid = ws-wa/ws-wl
Amount of solid at 1300C is therefore 50-45 / 58-45 = 5/13 = 0.385= 38.5%
Amount of liquid at 1300C is therefore 58-50 / 58-45 = 8/13 = 0.615 = 61.5%
Microstructures and Composition
Pro-eutectic phase is formed before the eutectic reaction, eg
a in the a+L region of phase diagram.
Lead Tin Microstructures
90 %Pb 10%Sn
70% Pb 30%Sn
38.1%Pb 61.9% Sn
50%Pb 50%Sn
Lead Tin Microstructures
15%Pb 85%Sn
Equiaxed Single Phase Grain Structure
Homeworks.
1.
2.
From the PbSn phase diagram, for a 70% Pb, 30%Sn alloy, at what temperature does
solid first form. At the eutectic temperature, how much proeutectic phase is present and
how much eutectic phase? What are the compositions at 100oC?
For a steel containing 0.4% C:a) At what temperature does austenite start to transform on cooling from 950oC?
b) How much proeutectoid phase is present at the eutectoid temperature
c) What is its composition?
d) Upon quenching the steel from 950oC to 50oC what phases will be present and what will
be the composition?