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-five
§ 5.18 Thompson’s tetrahedron
)000(,)21210(,)21021(,)02121( DCBA
§ 5.19 Reaction between Dislocation
? Ⅰ.Condition
1,Geometrical condition
2,Energy condition
?? ?
j
j
i
i bb
??
22 ?? ?
j
j
i
i bb
??
? Ⅱ.Example
1,(FCC)
]121[]112[]101[ 616121 ??
22
222
2222
3
1
2)
6
6
(
2
1
4
2
)
2
2
(
??
?
?
??
???
???
ji
j
j
i
i
bb
aab
aaab
??
?
?
]101[21?? ABb?
B
B
C
]211[
2,Lomer-Cottrell sessile dislocation
3,Dislocation network
4.
DDCA
DDBC
DDAB
a
?????
?????
?????
?
?
?
?? ??
?? ??
?? ??
)(:
)(:
)(:
)(at
ABDDCD
CADDBD
BCDDAD
d
3
1
:
3
1
:
3
1
:
)(at
???
???
???
????
????
????
§ 5.20 Simple Applications of
Dislocation Theory
? Ⅰ.Crystal Growth and Interfacial
Structure
1,Crystal Growth
Vapor —— Solid ; Liquid —— Solid
G
TTo
Gvap
Gsol
0c h i
v a ps o lc h i
?????
???
??
?SGVG
GGG
TSHG
TLK Model
The necessary supersaturation for crystal growth will be
smaller if the steps are available on the solid surface
Screw dislocation can provide such steps which will
never disappear in the course of growth.
2,Interfacial Structure
? Ⅱ.Small angle grain boundary (or
G.B,with small
misorientation) and grain
boundary strengthen.
1,Model for grain boundary
a,Tilt g.b.
b,Twist g.b.
c,General small angle boundary
2,Grain boundary strengthen and Hall-Petch
? Ⅲ.Strain hardening (work hardening)
? Ⅳ.Annealing (softening)
ρdecreases due to the annihilation of the dislocations of
opposite sign which can either slip or climb in annealing.
? Ⅴ.Alloy hardening
Solid Solution hardening (disorder)
homogeneous distribution
preferential distribution
A,Homogeneous distribution:
B,Preferential distribution
Resist to dislocation movement by the long-range
stress field induced by the solute atoms.
Examples and Discussions
Exercise
Thank you !
25
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-five
§ 5.18 Thompson’s tetrahedron
)000(,)21210(,)21021(,)02121( DCBA
§ 5.19 Reaction between Dislocation
? Ⅰ.Condition
1,Geometrical condition
2,Energy condition
?? ?
j
j
i
i bb
??
22 ?? ?
j
j
i
i bb
??
? Ⅱ.Example
1,(FCC)
]121[]112[]101[ 616121 ??
22
222
2222
3
1
2)
6
6
(
2
1
4
2
)
2
2
(
??
?
?
??
???
???
ji
j
j
i
i
bb
aab
aaab
??
?
?
]101[21?? ABb?
B
B
C
]211[
2,Lomer-Cottrell sessile dislocation
3,Dislocation network
4.
DDCA
DDBC
DDAB
a
?????
?????
?????
?
?
?
?? ??
?? ??
?? ??
)(:
)(:
)(:
)(at
ABDDCD
CADDBD
BCDDAD
d
3
1
:
3
1
:
3
1
:
)(at
???
???
???
????
????
????
§ 5.20 Simple Applications of
Dislocation Theory
? Ⅰ.Crystal Growth and Interfacial
Structure
1,Crystal Growth
Vapor —— Solid ; Liquid —— Solid
G
TTo
Gvap
Gsol
0c h i
v a ps o lc h i
?????
???
??
?SGVG
GGG
TSHG
TLK Model
The necessary supersaturation for crystal growth will be
smaller if the steps are available on the solid surface
Screw dislocation can provide such steps which will
never disappear in the course of growth.
2,Interfacial Structure
? Ⅱ.Small angle grain boundary (or
G.B,with small
misorientation) and grain
boundary strengthen.
1,Model for grain boundary
a,Tilt g.b.
b,Twist g.b.
c,General small angle boundary
2,Grain boundary strengthen and Hall-Petch
? Ⅲ.Strain hardening (work hardening)
? Ⅳ.Annealing (softening)
ρdecreases due to the annihilation of the dislocations of
opposite sign which can either slip or climb in annealing.
? Ⅴ.Alloy hardening
Solid Solution hardening (disorder)
homogeneous distribution
preferential distribution
A,Homogeneous distribution:
B,Preferential distribution
Resist to dislocation movement by the long-range
stress field induced by the solute atoms.
Examples and Discussions
Exercise
Thank you !
25
