CHAPTER 7: DISLOCATIONS AND STRENGTHENING
description
Transcript of CHAPTER 7: DISLOCATIONS AND STRENGTHENING
CHAPTER 7: DISLOCATIONS AND STRENGTHENING
EDGE DISLOCATIONS
SCREW DISLOCATIONS
CHARACTERISTICS OF DISLOCATIONS
SLIP SYSTEMS
SLIP IN SINGLE CRYSTALS
max(max) )cos(cos R
coscosR Resolved Shear Stress
Example ProblemConsider a single crystal of BCC iron oriented such that a tensile stress is applied along [010] direction.
Compute the resolved shear stress along a (110) plane and in a [ 11] direction when a tensile stress of 52 MPa is applied
1
STRENGTHENING BY GRAIN SIZE REDUCTION
yield o kyd 1/2
SOLID SOLUTION STRENGTHENING
SOLID SOLUTION STRENGTHENING
COLD WORKING
%CW
Ao AdAo
x100
Ao Ad
force
dieblank
force
-Forging -Rolling
-Extrusion-Drawing
tensile force
AoAddie
dieram billet
container
containerforce
die holder
die
Ao
Adextrusion
roll
AoAd
roll
COLD WORKING
• New crystals are formed that: --have a small disl. density --are small --consume cold-worked crystals.
33% coldworkedbrass
New crystalsnucleate after3 sec. at 580C.
Fig. 7.19 (a),(b), Callister 6e. (Fig. 7.19 (a),(b) are courtesy of J.E. Burke, General Electric Company.)
0.6 mm 0.6 mm
RECRYSTALLIZATION
• All cold-worked crystals are consumed.
After 4seconds
After 8seconds
Fig. 7.19 (c),(d), Callister 6e. (Fig. 7.19 (c),(d) are courtesy of J.E. Burke, General Electric Company.)
0.6 mm0.6 mm
FURTHER RECRYSTALLIZATION
GRAIN GROWTH
• Empirical Relation:
After 8 s,580C
After 15 min,580C
dn do
n Ktelapsed time
coefficient dependenton material and T.
grain diam.at time t.
exponent typ. ~ 2
0.6 mm 0.6 mm Fig. 7.19 (d),(e), Callister 6e. (Fig. 7.19 (d),(e) are courtesy of J.E. Burke, General Electric Company.)