Class 6 CHE 333

Phase Diagrams Continued

Prov08

Copper Zinc Phase Diagram

Peritectic reaction Liquid + solid 1 -> solid 2. Eutectoid reaction Solid 1 -> solid 2 + solid 3Maximum solid solubilty of zinc in copper is 38% at around 450C

1085C

420C

Substitutional Solid SolubiltyHow 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=0.144Crystal structure Ti- HCP, Al - FCCPoor soluility Na-Cl Na electronegativity 0.9, Cl 3.0Valences – Zn 2+, Cu 1+Only indicate solubility from these rules.

DOES NOT APPLY TO THE ELEMENTS H,C,O,N,B THESE FORM INTERSTITIALSOLID SOLUTIONS.

Iron Carbon Phase Diagram

SteelsEutectoidS1 -> S2 + S3-> + F e3C

PeritecticS1+L -> S2 + L ->

Fe3C- cementiteA compound

1538C

3367 SUBLIMES

Fe - then then C 1394C

Stainless Steel Phase Diagram

Ternary phase diagram for stainless steels. In this case an isothermal section at a constanttemperature 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-wlAmount 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

Lead Tin Microstructures90 %Pb 10%Sn

70% Pb 30%Sn

38.1%Pb 61.9% Sn

50%Pb 50%Sn

Lead Tin Microstructures15%Pb 85%Sn

Equiaxed Single Phase Grain Structure

Homework

• Using the Cu-Ni phase diagram, for a 50-50 Cu-Ni what are the compositions of the phases at 1400, 1300 and 1200 C and what phases would be present.

• Using the Pb- Sn phase diagram,what are the compositions for points “a,c and e” on the diagram?