Mechanisms of ?

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Mechanisms of ? Rafting in Single Crystal
Ni-Base Superalloys A Simulation Study
AFOSR under MEANS 2
Ning Zhou Chen Shen Michael J. Mills Yunzhi
Wang The Ohio State University
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Modeling of rafting in Ni Base superalloy

• Elastic model

Rafting direction is determined by the sign of
lattice misfit, modulus mismatch and applied load
direction.
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P type rafting

• Plastic-elastic model

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Take into account the contribution from plastic
deformation in?channels. And the rafting
direction is determined only by the sign of
lattice and applied load direction.
N type rafting
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Local stress field

• Rafting induced by channel dislocations for a
  homogeneous modulus system
• Rafting purely due to modulus mismatch with no
  channel dislocations
• Combining channel dislocations and modulus
  mismatch to evaluate their relative contributions.

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Starting configuration
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Dislocation structure
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(No Transcript)
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Negative misfit under tension
Time evolution of g' particles in a Ni-Al alloy
with -0.3 misfit under 152MPa tensile stress
along 001. Dislocations from different slip
systems are represented by different colors
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Positive misfit under tension
Time evolution of g' particles in a Ni-Al alloy
with 0.3 misfit under 152MPa tensile stress
along 001.
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Time evolution of g' particles in a Ni-Al alloy
with -0.3 misfit under 152MPa tensile stress
along 001. t3.6 hrs t7.2 hrs t10.7 hrs.
Dislocations from different slip systems are
represented by different colors
Time evolution of g' particles in a Ni-Al alloy
with 0.3 misfit under 152MPa tensile stress
along 001. t3.6 hrs t7.2 hrs.
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Chemical potential plot
Chemical potential difference in different
channels caused by channel dislocations is about
3050J/mol
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Effective Medium Approximation
D.Y. Li, L.Q. Chen, Scripta Materialia,
Vol.37,No.9,pp1271-1277,1997
Hard precipitate(Modulus mismatch about
40)Positive misfit 0.563
Discrete Atom Method
Jong K. Lee, Materials Science Engineering
A238(1997)1-12
Hard precipitate(Modulus mismatch50)Positive
misfit 5.0
Equivalent strain approach
Yu U. Wang, Yongmei M. Jin, and Armen G.
Khachaturyan J. App Phys. Vol 92, Number 31
(2002)1351-1360Phil Mag,  Vol  85 ,
Issue  23 ,( 2005)261-277
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2D simulation of rafting due toinhomogeneous
modulus
Hard precipitate Hard precipitate Hard precipitate Hard precipitate Soft precipitate Soft precipitate Soft precipitate Soft precipitate
Positive misfit Positive misfit Negative misfit Negative misfit Positive misfit Positive misfit Negative misfit Negative misfit
Comp Ten Com Ten Comp Ten Comp Ten

t
Initial relaxed misfit /-1.6)Modulus
mismatch 18
Applied stress /-0.03C440
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Negative misfit -1.6Modulus mismatch 18
Applied stress /-0.03C440
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Plastic V.S. Elastic
Channel dislocation induced rafting with
homogeneous modulus
Positive misfit Positive misfit Negative misfit Negative misfit
Comp Ten Com Ten
N P P N
competition
Rafting caused by inhomogeneous modulus
Hard precipitate Hard precipitate Hard precipitate Hard precipitate Soft precipitate Soft precipitate Soft precipitate Soft precipitate
Positive misfit Positive misfit Negative misfit Negative misfit Positive misfit Positive misfit Negative misfit Negative misfit
Comp Ten Com Ten Comp Ten Comp Ten
N P P N P N N P
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Questions?