1. Materials Moments: Arthur C—Food Containers Lewis & Ray—Al Composites

2. Exam I Friday 21 February Covers Chapters 1 – 7 Review Questions posted on Canvas

3. Strengthening Mechanisms Sections 7.8 – 7.13 Strengthening Metals

4. Underlying Principle for Strengthening Metals –Dislocations facilitate plastic deformation –Inhibiting (binding, stopping, slowing) dislocation motion makes metals stronger

5. Strengthening Metals: (Ways to restrict dislocation motion) Composition change: 1.Solid-solution strengthening (Diffusion) a)Case hardening b)Alloying

6. 1.Solid-solution strengthening (Diffusion) 2.Alloying Carburizing furnace

7. City Steel Heat Treating Co. Case Hardening – Hard Case w/ tough core Low-C Steels (> 0.30% C): Carburizing, Nitriding, Carbonitriding Carburized depth of 0.030 ” to 0.050 ” in 4 hours @ 1700°F

8. Alloying http://tankiialloy.en.made-in- china.com/offer/AqCnWidOrYcV/Sell-Copper-Nickel-Alloy- Strip.html Cu-Ni Alloy

9. f04_07_pg178 Atoms diffuse to a location that reduces strain energy Underlying principle:

10. f16_07_pg190 Fig. 7.17 Tensile strains Solid-Solution Strengthening: Smaller Substitutional Impurity

11. Solid-Solution Strengthening: Larger Substitutional Impurity Fig. 7.18 Compressive strains

12. 2. Solid-Solution Strengthening: Interstital Impurity Fig. 7.18 Compressive strains Fits in interstitial sites

13. 2. Solid-Solution Strengthening: Interstital Impurity Fig. 7.18 Compressive strains Fits in interstitial sites

14. Strengthening metals: How are dislocations bound in: Solid-solution strengthening? They seek sites near dislocations to reduce lattice strains. This stabilizes the lattice and discourages plastic deformation.

15. YouTube: Dislocation motion is analogous to the movement of caterpillar How Solid-Solution strengthening binds dislocations

16. f16_07_pg190 Cu-Ni alloy: Strength & Elongation Variation with Ni content Fig. 7.16

17. Strengthening Metals No Composition change: 1.Grain-size Reduction— Polycrystalline metals

18. f14_07_pg188 Grain size reduction: Dislocation motion at a grain boundary Fig. 7.14

19. Grain-size reduction Dislocation Pile-ups at grain boundaries Young Modulus and Yield Strength 2:11

20. Strengthening metals: How do we reduce grain size?

21. Strengthening metals: How are dislocations bound in: Grain-size reduction? It’s difficult for dislocations to move past a grain boundary The more grain boundaries, the more difficult for dislocations to move  metal is strengthened

22. Strengthening Metals: (Ways to restrict dislocation motion) 1.Solid-solution strengthening (Diffusion) 2.Grain-size reduction 3.Strain Hardening a.k.a. Work Hardening a.k.a. Cold Working

23. f05_07_pg179

24. 3. Strain Hardening (Work Hardening) (Cold Working) Includes (but not limited to) Drawing Rolling Peening— Strain hardened on surface only Strain hardened throughout No composition change

25. Strain Hardening in Copper

26. Cold Working Example: Wire Drawing YouTube: Wire Drawing “2.Combined Drawing Machine SH-1” 0:20 - 0:45 YouTube: Drawing Process in Manufacturing / Aluminium tube Production

27. f16_07_pg190 Cold Working Example: Drawing 2. Deep drawing of sheet metal, Tiefziehen von Metallblechen 1. Deep drawing of sheet metal, Tiefziehen von Metallblechen YouTube:

28. Strain Hardening: Example: Rolling

29. f16_07_pg190 Cold Working Example: Shot peening

30. Cold Working Example: Shot peened surface

31. Dislocation Densities Plastic Deformation: Stainless Steel

32. Strengthening due to Cold Work Fig. 7.19

33. f20_07_pg193

34. Strengthening metals: How are dislocations bound in: Strain hardening?

35. f05_07_pg179 Increasing the dislocation density increases the number of dislocations which can repel each other.

36. f05_07_pg179 Plastic Deformation difficult Dislocations can’t easily move Metal is Strengthened Strain Hardening

37. Recovery, Recrystallization, & Grain Growth Sections 7.10 – 7.13 Reverse of Strengthening

38. Annealing: Eliminates dislocations 1) Recovery 2) Recrystallization 3) Grain Growth

39. f21d_07_pg197 Recrystallization 580ºC Stages of Recrystallization and grain growth 33% Cold-worked brass (T m = 900-940ºC) t = 3 sect = 0t = 4 sec

40. f21d_07_pg197 Grain size increases Stages of Recrystallization and grain growth Cold-worked brass t = 8 sec (580ºC)t = 15 min (580ºC)t = 10 min (700ºC)

41. Recovery followed by grain growth in polycrystalline camphor-ethanol mixture YouTube Video:

42. f11_07_pg186 Plastic Deformation: Polycrystalline Cold-worked Nickel Before deformationAfter deformation Fig. 7.11--170x photomicrograph

43. Controlled annealing Strain-relaxed buffers due to annealing in Silicon

44. f16_07_pg190 Recovery, Recrystallization, and Grain Growth Recovery (grains recover slightly from cold- working) Recrystal -lization (new grains form) Grain Growth (larger grains grow at expense of smaller) See Fig. 7.22

45. YouTube: Tensile Test on Work-Hardened Copper: necking effectTensile Test on Work-Hardened Copper: necking effect YouTube: Tensile Test on Annealed CopperTensile Test on Annealed Copper Compare these videos: Take note of the knurled knob on the RHS

46. How do we restore ductility to work hardened metals? Eliminate Dislocations!

47. Some little study aids follow

48. Review on your own: When Strengthening metals: How are dislocations bound in these cases? 1)Grain-size reduction 2)Solid Solution Strengthening 3)Strain hardening

49. ElementCrystal structureAtomic radius Fe BCC 0.124 nm Cr BCC0.125 nm AlFCC0.125 nm NHCP0.065 nm a) N in Fe at 700°C b) N in Fe at 900°C c) Cr in Fe at 700°C d) Cr in Fe at 900°C e) Al in Fe at 700°C f) Al in Fe at 900°C 1. For which combination of metals do you expect solid solution strengthening to occur? 2. For which combination of metals do you expect diffusion to be the fastest?

50. Metallic xl Structures 1) Face-Centered Cubic (FCC) Cu, Al, Ag, Au, Pb, Ni, Pt 2) Body-Centered Cubic (BCC) Na, Fe, Cr, Mo, W § Hexagonal Close-Packed (HCP) Ti, Zn, Cd, Co, Mg