材料科学基础
Fundamental of Materials
Prof,Tian Min Bo
Tel,62795426, 62772851
E-mail,tmb@mail.tsinghua.edu.cn
Department of Material Science and Engineering
Tsinghua University,Beijing 100084
Lesson twenty-two
§ 5.12 Interaction between
Dislocation and Point Defect
By cottrell atmosphere model,we can explain
the sharp yielding phenomenon.
EEf
p
rRpVpE
zyx
g r a d
)(
3
1
)(
3
4 33
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????
??????
??
?
???
?
Cottrell Atmosphere
Strain aging
Point defect Cottrell Atmosphere
(strain aging)－－ BCC
?
?
§ 5.13 Multiplication of dislocations
? Ⅰ.What ’s multiplication and why is
it needed?
? Ⅱ.Key points of the mechanisms of
the multiplication.
1,The dislocation does not lie entirely on the
same slip plane.
2,Part of the dislocation segments can not move
for either of the following reasons.
a,No applied stress
b,The plane on which the segment would move is not
allowed crystallographically.
c,There is strong obstacles around the segment.
? Ⅲ.Frank -Read mechanism or F-R source.
1,F-R mechanism,L- shaped dislocation.
2,F-R source.
?
?
?
?
?
???
????
?
Gb
b
Gb
b
T
bT
blbTf r
??????
???
2
dd
2
d
s i n2
When dislocation is in quasi-static equilibrium
When dislocation will spontaneously slip
)2( L
Gb?? ?
)2( L
Gb?? ?
Examples and Discussions
Exercise
Thank you !
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