ning zhou; chen shen; michael j. mills ; yunzhi wang; the ohio state university afosr under means 2...
TRANSCRIPT
Ning Zhou; Chen Shen; Michael J. Mills ; Yunzhi Wang;
The Ohio State University
AFOSR under MEANS 2
Mechanisms of ’ Rafting in Single Crystal Ni-Base Superalloys
––– A Simulation Study
Modeling of rafting in Ni Base superalloy
•Elastic model
•Plastic-elastic model
Rafting direction is determined by the sign of lattice misfit, modulus
mismatch and applied load direction.
Take into account the contribution from plastic deformation inγchannels. And the rafting direction is determined only by the sign of lattice and applied load direction.
P type rafting
N type rafting
γ’
γ
/ E
2( ) /E E E
Local stress field
External applied stress
Dislocationconfiguration Microstructure
StressField
Misfit stressDislocation stress
Dislocation movement
Microstructureevolution
Initial channel filling and relaxation: PF dislocation model
Rafting: PF binary diffusion model
)( 321
Stress due to
modulus mismatch Modulus mismatch between /’
• 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.
Starting configuration
Dis
loca
tion
stru
ctur
e
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
Negative misfit under tension
Time evolution of g' particles in a Ni-Al alloy with +0.3% misfit under 152MPa tensile stress along [001].
Positive misfit under tension
Time evolution of g' particles in a Ni-Al alloy with -0.3% misfit under 152MPa tensile stress along [001]. t=3.6 hrs; t=7.2 hrs; t=10.7 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]. t=3.6 hrs; t=7.2 hrs.
Chemical potential difference in different channels caused by channel dislocations is about 30~50J/mol
Chemical potential plot
Effective Medium Approximation
Hard precipitate(Modulus mismatch about 40%)
Positive misfit: 0.563%
Discrete Atom Method
Hard precipitate(Modulus mismatch:50%)
Positive misfit: 5.0%
Jong K. Lee, Materials Science & Engineering A238(1997)1-12
D.Y. Li, L.Q. Chen, Scripta Materialia, Vol.37,No.9,pp1271-1277,1997
Yu U. Wang, Yongmei M. Jin, and Armen G. KhachaturyanJ. App Phys. Vol: 92, Number 31 (2002)1351-1360Phil Mag, Vol: 85 , Issue: 2–3 ,( 2005)261-277
Equivalent strain approach
Hard precipitate Soft precipitate
Positive misfit Negative misfit Positive misfit Negative misfitComp Ten Com Ten Comp Ten Comp Ten
Initial relaxed: misfit: +/-1.6%)Modulus mismatch: 18%
2D simulation of rafting due toinhomogeneous modulus
Applied stress: +/-0.03C440
t*
2( ) /E E E
No applied stress
Soft precipitate
No applied stress
hard precipitate
Negative misfit: -1.6%Modulus mismatch: 18% Applied stress: +/-0.03C44
0
Hard precipitate Soft precipitatePositive
misfitNegative
misfitPositive
misfitNegative
misfitComp Ten Com Ten Comp Ten Comp Ten
N P P N P N N P
Plastic V.S. Elastic
Channel dislocation induced rafting with homogeneous modulus
Positive misfit
Negative misfit
Comp Ten Com Ten
N P P N
Rafting caused by inhomogeneous modulus
/ E
2( ) /E E E
competition