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 sixteen
§ 4.9 Comparison Between Slip and
Twinning
? Ⅰ.Similarity:
Both slip and twinning are shear process under shear
stress,
? Ⅱ.Differences:
1,Orientation
2,Atom movement
3.
4,Conditions:
?
l?,?
a) Structure,Twinning is easy
b) Temperature:
c) Strain rate )ddor(dd tt ??
5,Surface morphology:
Etching treatment with an etchant removes slip steps
leaving no trace,but reveals twins by delineating the
interface between the twin and the matrix.
6,Conditions:
① Structure,twinning is easy to take place in
crystals of low symmetry.
② Temperature
③ Strain rate
td
d?
7,Twinning plays an essential role in BCC and HCP
lattices.
§ 4.10 Basic Features of The Plastic
Deformation of Polycrystals
Basic distinction between single crystal and polycrystals
① A great deal of grains with different orientation
② Grain boundary
G.B,is a thin layer of material between neighboring
grain where atoms arranged in transitional position.
single crystal polycrystal
grain
grain
boundary
? Ⅰ.Grain boundary and its role in
deformation
① Impede slip (as obstacles) at R.T,and low temperature.
② Coordinate the deformation in different grains.
③ Enhance (assist) the plastic deformation at high
temperature through grain boundary sliding.
b?
grain
.b.g
TetT
There exists an Equicohesive
Temperature at which
)g r a in(b.)b.g(b ?? ?
met 5.0 TT ?
? Ⅱ.Deformation features of polycrystal
? Plastic deformation can take place in various ways.
slip,twinning,g.b,sliding,migration,diffusion
② Multislip + rotation.
? Ⅲ.Internal stress (residual stress)
1,Definition:
2,Formation:
3,Classification:
Baushinger effect:
Previous extension will increase the strength in
subsequent extension while decrease the strength in
subsequent compression.
macroscopic
microscopic
1 2
3
5
4
6
②⑥ 软位向,μ大，已发生塑性变形
①③ 硬位向,μ小，未发生塑性变形
? Ⅳ.Strain hardening (or work -
hardening)
1,The increase of strength of materials with strain is
called strain hardening,It is shown by curve.
2,Hall-Petch formula,
Where and k are material constant.
d,The size of grains,(diameter)
???
21??? kdoys ??
??
r a t eh a r de n in gdd ??
? Ⅴ.Morphology
1,Band structure.
2,Orange peal structure due to the different in account
of deformation between grain center and grain
boundary.
3,Fibre structure (mechanical texture).
In plastic deformation,both the grains and the
impurities or second phases may be elongated along
the principal direction of flow,forming fibre structure.
? Ⅵ.Preferred orientation
(crystallographic texture)
1,Definition:
If certain crystallographic directions (or planes) of
grains in polycrystalline material aligned to a common
reference directions (or planes) the material is said to
have preferred orientation.
2,Description
① By indicating the ideal position <u v w> or {h k l}
② By pole figure
compression cold drawing& extrusion rolling
FCC <110> <111>+<100> {110}<112>
BCC <111>+<100> <110> {100}<110>
HCP [0001] Depends on c/a?? 0110
3,Classification:
Deformation texture Single texture
Annealing texture Double texture
Rolling texture Wire texture
Compression texture Sheet texture
4,Cause of formation.
Rotation accompanying slip (+ twinning)
Examples and Discussions
1,
R.D.
T.D.
① What is pole figure?
{001} pole figure of Al sheet with {001}<100>
② Preferred Orientation
③ Deep drawing
④ Anisotropy
under σ1 under σ2
S.S.
cosФ
cosλ
]110)[111(]101)[111(
]011)[111(]110)[111(
]110)[111(]011)[111(
]110)[111(]101)[111(
]110)[111(
]101)[111(
]011)[111(
]101)[111(
2
1
3
1
6
1??
2
1
6
2
6
1??
2,
R.D.
T.D.
(0001) pole figure for Zn
N.D.
R.D.
T.D.
(0001) pole figure for Mg
N.D.
① What is the different between this two pole figures?
② Only c/a is different.
③ Initial state
disordered polycrystal
Exercise
Thank you !
16
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 sixteen
§ 4.9 Comparison Between Slip and
Twinning
? Ⅰ.Similarity:
Both slip and twinning are shear process under shear
stress,
? Ⅱ.Differences:
1,Orientation
2,Atom movement
3.
4,Conditions:
?
l?,?
a) Structure,Twinning is easy
b) Temperature:
c) Strain rate )ddor(dd tt ??
5,Surface morphology:
Etching treatment with an etchant removes slip steps
leaving no trace,but reveals twins by delineating the
interface between the twin and the matrix.
6,Conditions:
① Structure,twinning is easy to take place in
crystals of low symmetry.
② Temperature
③ Strain rate
td
d?
7,Twinning plays an essential role in BCC and HCP
lattices.
§ 4.10 Basic Features of The Plastic
Deformation of Polycrystals
Basic distinction between single crystal and polycrystals
① A great deal of grains with different orientation
② Grain boundary
G.B,is a thin layer of material between neighboring
grain where atoms arranged in transitional position.
single crystal polycrystal
grain
grain
boundary
? Ⅰ.Grain boundary and its role in
deformation
① Impede slip (as obstacles) at R.T,and low temperature.
② Coordinate the deformation in different grains.
③ Enhance (assist) the plastic deformation at high
temperature through grain boundary sliding.
b?
grain
.b.g
TetT
There exists an Equicohesive
Temperature at which
)g r a in(b.)b.g(b ?? ?
met 5.0 TT ?
? Ⅱ.Deformation features of polycrystal
? Plastic deformation can take place in various ways.
slip,twinning,g.b,sliding,migration,diffusion
② Multislip + rotation.
? Ⅲ.Internal stress (residual stress)
1,Definition:
2,Formation:
3,Classification:
Baushinger effect:
Previous extension will increase the strength in
subsequent extension while decrease the strength in
subsequent compression.
macroscopic
microscopic
1 2
3
5
4
6
②⑥ 软位向,μ大，已发生塑性变形
①③ 硬位向,μ小，未发生塑性变形
? Ⅳ.Strain hardening (or work -
hardening)
1,The increase of strength of materials with strain is
called strain hardening,It is shown by curve.
2,Hall-Petch formula,
Where and k are material constant.
d,The size of grains,(diameter)
???
21??? kdoys ??
??
r a t eh a r de n in gdd ??
? Ⅴ.Morphology
1,Band structure.
2,Orange peal structure due to the different in account
of deformation between grain center and grain
boundary.
3,Fibre structure (mechanical texture).
In plastic deformation,both the grains and the
impurities or second phases may be elongated along
the principal direction of flow,forming fibre structure.
? Ⅵ.Preferred orientation
(crystallographic texture)
1,Definition:
If certain crystallographic directions (or planes) of
grains in polycrystalline material aligned to a common
reference directions (or planes) the material is said to
have preferred orientation.
2,Description
① By indicating the ideal position <u v w> or {h k l}
② By pole figure
compression cold drawing& extrusion rolling
FCC <110> <111>+<100> {110}<112>
BCC <111>+<100> <110> {100}<110>
HCP [0001] Depends on c/a?? 0110
3,Classification:
Deformation texture Single texture
Annealing texture Double texture
Rolling texture Wire texture
Compression texture Sheet texture
4,Cause of formation.
Rotation accompanying slip (+ twinning)
Examples and Discussions
1,
R.D.
T.D.
① What is pole figure?
{001} pole figure of Al sheet with {001}<100>
② Preferred Orientation
③ Deep drawing
④ Anisotropy
under σ1 under σ2
S.S.
cosФ
cosλ
]110)[111(]101)[111(
]011)[111(]110)[111(
]110)[111(]011)[111(
]110)[111(]101)[111(
]110)[111(
]101)[111(
]011)[111(
]101)[111(
2
1
3
1
6
1??
2
1
6
2
6
1??
2,
R.D.
T.D.
(0001) pole figure for Zn
N.D.
R.D.
T.D.
(0001) pole figure for Mg
N.D.
① What is the different between this two pole figures?
② Only c/a is different.
③ Initial state
disordered polycrystal
Exercise
Thank you !
16
