1. Phase Diagrams Chapter 9 4 th Edition Chapter 10 5 th Edition

2. So far…. We have concentrated on the solidificaton of a pure metal. We have looked at strengthening approaches that do not require that we change the composition of the metal. In this chapter we start to examine alloying, and see why alloys are stronger than pure metals

3. Let’s Start with a basic question.. What is a phase? Homogeneous in crystal structure and atomic arrangement Same physical and chemical properties A definite interface with its surroundings Mechanically separable

4. For example A glass of ice water has two phases Solid water phase Liquid water phase Homogeneous in crystal structure and atomic arrangement Same physical and chemical properties A definite interface with its surroundings Mechanically separable

5. A mixture of salt and pepper has two phases Solid salt Solid pepper Homogeneous in crystal structure and atomic arrangement Same physical and chemical properties A definite interface with its surroundings Mechanically separable

6. Solid, Liquid or Gas? We usually think of matter as having 3 phases, but.. It’s possible to have more than one solid phase. For example at atmospheric pressure when iron first freezes it is BCC As it cools it changes to FCC Upon further cooling it changes to BCC

7. Phase Diagram A visualization technique to help you see where different phases exist, based on “state variables” Solid Liquid Gas Pressure Temperature Typical phase diagram – for example for Carbon Dioxide

8. Phase Diagram A visualization technique to help you see where different phases exist, based on “state variables” Solid Liquid Gas Pressure Temperature Phase diagram for pure water ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.

9. http://www.enm.bris.ac.uk/teaching/projects/ 2002_03/jb8355/review.html

10. From the following article: Superconductivity: Iron cast in exotic role S. S. Saxena and Peter B. Littlewood Nature 412, 290-291(19 July 2001) doi:10.1038/35085681

11. We are going to start with Solidification from a Melt of… Binary Isomorphous (single solid phase) Metals What we learn also applies to ceramics In the next chapter we’ll look at phase diagrams that include multiple solid phases

12. Binary Isomorphous Phase Diagrams for Metal Alloys Temperature XY % Y added Liquid Solution Solid Solution Two Phase Constant Pressure!!!

13. Phase Diagrams Nomenclature Temperature XY % Y added Liquidus Solidus Freezing Range

14. Temperature Time Cooling Curve for Simple Alloys Liquid Two Phase Solid Temperature XY % Y added Isopleth

15. What Constitutes a Simple Alloy? A single phase solid solution of two or more metals Most metals are alloys But what is a solid solution?

16. Solutions We usually think of liquid solutions Pour alcohol into water and it dissolves Alcohol and water are completely miscible Miscible means completely soluble ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.

17. Limited Solubility Salt is a solid, but it dissolves in water too. Eventually though, you can’t add any more salt, and you get a two phase system (What are the two phases?) Solid and Liquid But its not pure water and solid salt – its salt water and solid salt ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.

18. Insoluble Species Oil and water don’t mix Does that mean there is absolutely no oil in the water, or that there’s no water in the oil? Absolutely not!! It just means that not very much dissolved. This is a two phase system too – they are both liquid phases ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.

19. Solid Phases You can dissolve one solid in another One way we’ve looked at dissolving one solid in another in the past is through diffusion Now we’ll look at forming a solid solution as the metals solidify

20. Solids have varying solubility – just like liquids Copper and nickel are completely soluble (miscible) in each other Copper and Zinc display limited solubility Lead and copper are considered insoluble Why?

21. Consider liquid solubility Like dissolves like Water and Alcohol are miscible because they are similar chemically (polar molecules) Water and Oil are immiscible because they are different (polar vs non-polar)

22. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license. Melt Single Phase Solid Solution Two solid phases – each of which are solutions

23. Solubility Rules Hume-Rothery Rules Size – up to a 15% difference in radius Crystal Structure – the same Valence – the same Electronegativity – Approximately the same If these conditions are met, the two metals are usually completely soluble These rules also apply to ceramics There is a quiz on the CD what came with your text - use it to practice

24. Consider Copper and Nickel Size – up to a 15% difference in radius Crystal Structure Valence Electronegativity Radius Cu = 1.278 A Radius Ni = 1.243 A FCC vs FCC Cu -- +1 or +2 Ni -- +2 1.9 vs 1.9

25. Consider Copper and Zinc Size – up to a 15% difference in radius Crystal Structure Valence Electronegativity Radius Cu = 1.278 A Radius Zn = 1.332 A FCC vs HCP Cu -- +1 or +2 Zn -- +2 1.9 vs 1.6 Therefore not TOTALLY miscible

26. Consider Copper and Lead Size – up to a 15% difference in radius Crystal Structure Valence Electronegativity Radius Cu = 1.278 A Radius Pb = 1.75 A FCC vs FCC Cu -- +1 or +2 Pb -- +4 1.9 vs 1.9 Copper and Lead are essentially insoluble

27. Solid Solution Strengthening Purposely add an element into the crystal lattice It distorts the lattice, which causes strengthening The bigger the distortion, the bigger the improvement in strength Remember, really large atoms or really small atoms will not be completely soluble

28. Effect of adding an impurity Be Si Sn Al Ni Zn MetalRadius (A)(r-r Cu )/r Cu *100 Cu1.278 Zn1.332+4.2% Al1.432+12.1% Sn1.509+18.1% Ni1.243-2.7% Si1.176-8.0% Be1.143-10.6%

29. Adding a small substitutional atom

30. Distorts the Matrix

31. Adding a large substitutional atom

32. Distorts the Matrix

33. Effect of adding an impurity Be Si Sn Al Ni Zn MetalRadius (A)(r-r Cu )/r Cu *100 Cu1.278 Zn1.332+4.2% Al1.432+12.1% Sn1.509+18.1% Ni1.243-2.7% Si1.176-8.0% Be1.143-10.6%

34. Other Property Effects Property Tensile strength Yield Strength % Elongation Electrical Conductivity Direction Up Down Try the quiz on the CD that came with your text

35. Strength (psi) CuNi Wt % Nickel 60% Ni Look at the Effect on Yield Strength Monel Inexpensive valve showing corrosion ?

36. Use a phase diagram to examine the solidification process in more detail Temperature XY % Y added Tie Line Lever Law Isopleth A B C

37. Temperature XY % Y added 30 % 70% 20% Sample Calculation Overall Composition Composition of the solid Composition of the liquid

38. All Liquid 52% Ni 45% Ni Solidification Process of Cu - 40% Ni Melt Almost 40% Ni 40 % Ni Can only happen if the melt is cooled slowly Diffusion keeps the solid a constant composition and must have time to occur

39. Microsegregation occurs if solidification happens more quickly Can lead to “hot shortness” The melting point is different at each point in the solid because the composition is different

40. Homogenization If after the solid has formed it is reheated, what happens? Diffusion! The microsegragation can be eliminated

41. Microsegregation can be eliminated with heating

42. Macrosegregation In a casting, the sides solidify first Because of this, the sides may have a different composition that the middle of the casting Can not be eliminated by an homogenization treatment Hot working will take care of it

43. Phase Diagrams You’ll need some phase diagrams to practice with, and for your homework Use the ones in the textbook However…here are some examples for us to play with now