chp7 - CHAPTER 7 DISLOCATIONS AND STRENGTHENING ISSUES TO...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Chapter 7- Slides adapted from J Wiley material ISSUES TO ADDRESS. .. • Why are dislocations observed primarily in metals and alloys? • How are strength and dislocation motion related? • How do we increase strength? 1 • How can heating change strength and other properties? CHAPTER 7: DISLOCATIONS AND STRENGTHENING Chapter 7- Slides adapted from J Wiley material 2 • Metals: Disl. motion easier. -non-directional bonding -close-packed directions for slip. electron cloud ion cores • Covalent Ceramics (Si, diamond): Motion hard. -directional (angular) bonding • Ionic Ceramics (NaCl): Motion hard. -need to avoid ++ and -- neighbors. DISLOCATIONS & MATERIALS CLASSES
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
2 Chapter 7- Slides adapted from J Wiley material 3 • Produces plastic deformation at T < T m /3 • Incrementally breaks bonds. Plastically stretched zinc single crystal. • If dislocations don't move, deformation doesn't happen! Adapted from Fig. 7.1, Callister 6e. (Fig. 7.1 is adapted from A.G. Guy, Essentials of Materials Science , McGraw-Hill Book Company, New York, 1976. p. 153.) Adapted from Fig. 7.9, (Fig. 7.9 is from C.F. Elam, The Distortion of Metal Crystals , Oxford University Press, London, 1935.) Adapted from Fig. 7.8, DISLOCATION MOTION Chapter 7- Slides adapted from J Wiley material Making dislocations hard to move ought to 1. increase elastic modulus 2. increase ductility 3. increase yield strength
Background image of page 2
3 Chapter 7- Slides adapted from J Wiley material 4 • Crystals slip due to a resolved shear stress, τ R . • Applied tension can produce such a stress. ! R = " cos # cos $ ! n s A A s STRESS AND DISLOCATION MOTION s l i p d r e c t o n slip plane normal, n s Chapter 7- Slides adapted from J Wiley material 5 • Condition for dislocation motion: ! R > ! CRSS • Crystal orientation can make it easy or hard to move disl. 10 -4 G to 10 -2 G typically ! R = " cos # cos $ CRITICAL RESOLVED SHEAR STRESS
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
4 Chapter 7- Slides adapted from J Wiley material 6 • Slip planes & directions ( λ , φ ) change from one crystal to another. τ R will vary from one crystal to another. • The crystal with the largest τ R yields first. • Other (less favorably oriented) crystals yield later. Adapted from Fig. 7.10, Callister 6e. (Fig. 7.10 is courtesy of C. Brady, National Bureau of Standards [now the National Institute of Standards and Technology, Gaithersburg, MD].) 300 μ m DISL. MOTION IN POLYCRYSTALS σ Chapter 7- Slides adapted from J Wiley material 7 • Grain boundaries are barriers to slip. • Barrier "strength" increases with misorientation. • Smaller grain size d : more barriers to slip.
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 16

chp7 - CHAPTER 7 DISLOCATIONS AND STRENGTHENING ISSUES TO...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online