NiAl

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2006-9-27
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• ??????? ( ???? )
• ????
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• ??-?????????

Fe
NiAl
????????????????

• ????? (MD)
• ??????? (MDFE)
• ??????????????
• ????????(MDFECMMMM)

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MD
Abraham et al., PNAS
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Brittle fracture in bcc-iron
Stacking fault (SF)
Anisotropy for cleavage fracture
KI1.6KIC
(a) 010 lt101gt, KI1.11KIC (b) 110 lt101gt,
KI1.27KIC (c) 110 lt001gt, KI1.49KIC (d) 010
lt001gt, KI1.9KIC
Twinning
0.1KIC/300? 0.1KIC/800?
0.1KIC/4000?
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Brittle to ductile transition
5K
100K
KI2.2KIC
200K
300K
Guo Y-F, Wang C-Y, Zhao D-L. Mater Sci Eng A,
2003,349(1-2)29 Y-F Guo, C-Y Wang, Y-S Wang.
Phil. Mag. Lett, 2004, 84(12)763 ??????,
????,?????,2003,p360-366
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?????? ???????
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A100 lt110gt B110 lt110gt C111 lt110gt
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procedure


different loads
Get initial cracks according to continuum
mechanics
different types of crack
Plane strain condition
Relax the crack by MD
F-S N-body potential
fixed-displacement boundary condition
Observe the structure evolution of the crack tip
4000 steps
510-15s
bcc-Iron
37nm-37nm
Length of crack 3.7nm
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Initial crack
Anisotropic linear elastic continuum theory
Displacement field u
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Crack tip field for plane strain condition
G.C. Sih, H. Liebowitz (ed.), in Fracture An
Advanced Treatise (vol.2), Academic, New York,
1968, p67.
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Structure evolution of the crack tip for
different types of cracks
A100 lt110gt crack B110 lt110gt crack
C111 lt110gt crack
KI 1.9 KIC

• the stress-induced phase transformation or
  recrystallisation can only occurs at KI gt1.8 KIC

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bcc-hcp
B 110 lt110gt crack
partial dislocations emission on
successive planes
C 111 lt110gt crack
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90 steps
110 steps
140 steps
B 110 lt110gt crack
40 steps
80 steps
140 steps
C 111 lt110gt crack
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Phase transformation
a 2.8665 Å to 2.733 Å
b 4.0525 Å to 4.7336 Å
bcc
hcp
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• new grain nucleated with a different orientation
  from the original bcc crystal (90?)

• boundary between the twin strip and the new
  grain is a lt110gt symmetrical tilt boundary with
  the rotation angle of 70.5?

A 100 lt110gt crack
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New grain nucleation
and
20 steps
60 steps
140 steps

• new grain grows with the growth of two twin
  regions, and the lengths of the new grain in
  and directions are always equal to the
  thickness of the twin region

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Distribution of shear stress
A 100 lt110gt crack B 110 lt110gt crack
B
A
C
symmetric
C 111 lt110gt crack
unsymmetric
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• ????????????????????????????????????????????????
  ??????,???????????
• ??????????hcp?????hcp??????bcc???? (0.11eV/atom)
  ,?????????????????

• ????
• ????
• ????????????

Y-F Guo, Y-S Wang, D-L Zhao. Acta Materialia
(in press)
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Phase transformation in NiAl
B2
110 crack plane is the only cleavage plane in
B2 NiAl (MD, experiments)
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B2-L10
100 lt001gt crack
110 lt001gt crack
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110 lt110gt crack
100 lt110gt crack
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??-???????????? ??????
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???????????
010lt100gt??
?????????UY, UX???r????
?????????dy , dx ???r????
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• ???????????????????,????????????????

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???????????????
010lt101gt??
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???????????????????????
KI 1.6KICLY?????Y????
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???????????????
LY29Å
KI1.2KIC
KI1.6KIC
KI1.9KIC
LY57Å
KI1.9KIC
KI1.2KIC
KI1.6KIC
KI1.1KIC
LY140Å
KI1.6KIC
KI1.9KIC
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???????????????
KI 1.9KIC (a)LY140Å(b)LY280Å(c)LY360Å
Y-F Guo, Y-C Gao. Computational Materials
Science, 2006, 36432-439.
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??

• ??????????????????????100 Å?????,
  ???????????????100 Å
• ?????????300Å,????????????????bcc-Fe?????????????
  ?
• ???????300Å (30nm)????????

?? ??
??????
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• ???-????????????
• ????????
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?????????,?????????a????????,a?????????
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??????
????1.2KIC
???500??????????????
(a)??500??????? (b)??4000???????
KI 1.4KIC

• ????1.4KIC????????????

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• ? (????) ? ( ????/ )
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????
????
?/?? (70???) ??? (0.3-0.5µm ) ? ?? (??)
,???????????
????
????
?/
??????????,???1100K??,???????????????,???????????
?????????????,?????????????? (????????????????
?????)
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• ????? (MD) ??????? (MDFE)
• ??????????????
• ????????(MDFECMMMM)

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Size? Temperature? Stress?
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tensile stress of 300Mpa
the critical external tensile stress of about
180Mpa is required for bowing a creep dislocation
in the horizontal matrix channel at 950?
W-P Wu,Y-F Guo, Y-S Wang. Transactions of
Nonferrous Metals Society of China (accepted)
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????????????973????????????!
THANKS FOR YOUR ATTENTION!