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-three
§ 5.14 Pile up of Dislocation
? Ⅰ.Model
? Ⅱ.Back stress exerted by obstacle on
leading dislocation.
(It is supposed to be a short-range-force.)
??
??
n
xbxbn
B
B
??
? dd dx, virtual displacement
? Ⅲ.Distribution of the dislocation
),,3,2(0
1
)1(21
nibb
xx
Gb
ii
ji
n
ij
j
j ?????????
??
?
?
?
?
??
To leading dislocation,
0
)(
1
)1(2 1112
???
????
bbb
x
Gb
B
j
n
j
j ??
??
? Ⅳ.Consequence
① Cut through obstacle
② Bypass
③ Crack
by slip
by climbing
by cross slip
§ 5.15 Intersection of Dislocations
? Ⅰ.Rule:
When two dislocation moving on intersecting slip planes
meet together,their shape will in general change,This
shape change can be determined by the macroscopic
deformation of the crystal.
? Ⅱ.Examples:
1,⊥ -⊥ Burgers vector ⊥ forming jog
2,⊥ -⊥ Burgers vector ∥ forming kink
3,⊥ -$ forming one jog,one kink,or two jogs
4,$-$ forming two jogs
A
B
C D1b
?
2b? ??
A
B
C D
1b?
2b?
A
B
C D
1b
?
2b?
? Ⅲ.Consequence
1,No change in dislocation shape ＝ > no effect
on further slip.
2,Formation of jog.
① Which could slip along with the remaining segments,
but on different S.P,the consequence depends on the
height of jog.
a,Short jog (1~2?) is effect in slip.
b,Long jog (>100?) forming L-shaped dislocation sources.
c,Mediums jog (<100?) forming dislocation dipole.
② Which must climb along with the remaining segments,
The consequence is
a,leaving point defects
b,hardening
Examples and Discussions
Exercise
Thank you !
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