a comparison of the electron and ion irradiation effects on the stability range of ordered...
TRANSCRIPT
A COMPARISON OF THE ELECTRON AND ION IRRADIATION EFFECTS ON THE
STABILITY RANGE OF ORDERED
STRUCTURES IN Ni4 Mo
M. SUNDARARAMAN* and S. BANERJEE
Presented by G. K. DEY
Materials Science Division
Bhabha Atomic Research Division
Mumbai 400085
* email:[email protected]
Outline
•Ordering – chemical, magnetic, & electric• Evolution of Ordering• Competing superlattices in Ni4Mo alloy• Influence of radiation on order disorder• Order evolution
-- under electron irradiation
-- under heavy ion irradiationComparison of electron and ion irradiation results
Conclusions
Ordering – Chemical, ferromagnetic, ferroelectric
Chemical Ordering
FerromagneticFerroelectric Ordering
Emptylattice
Atoms A & B
Electric/magneticmoments
Outline
•Ordering – chemical, magnetic, & electric• Evolution of Ordering• Competing superlattices in Ni4Mo alloy• Influence of radiation on order disorder• Order evolution
-- under electron irradiation
-- under heavy ion irradiationComparison of electron and ion irradiation results
Conclusions
Evolution of order
Nucleation and Growth
Continuous Ordering
Order evolution could be either first or second order
Evolution of Ordering – Static Concentration Waves
Single Variant <100> K vector – B2 Ordering
3 variants <100> K vector
– L12 ordering
First & second order transitions: Thermodynamic viewpoint
nth order transformation: 0T/F;0T/F 1n1nnn
F
E
Cp
Temperature
First Order Second order
Energy barrierNucleation & growth
First & second order transitions: Landau Plots
First Order(Discrete)
Second order(Continuous)
Outline
•Ordering – chemical, magnetic, & electric• Evolution of Ordering• Competing superlattices in Ni4Mo alloy• Influence of radiation on order disorder• Order evolution
-- under electron irradiation
-- under heavy ion irradiationComparison of electron and ion irradiation results
Conclusions
Ordered States in Ni4 Mo
* Above 1140 K alloy is in SRO state
* Below 1140 K alloy is in LRO state
* By conventional solutionising and quenching treatment alloy can not be produced in the completely disordered state (CDO)
* LRO and SRO are two different states
Description of LRO and SRO structures
}]2/)2/1p({sin s 2 1 [ c Cp
[001] Projection
LRO state
SRO state
]5/pCos4 5/pCos2 l 2 1 [ c Cp
p = 0,1,2,3 for <1 ½ 0> modulation
p = 0,1,2,3, 4 for 1/5<1 ½ 0> modulation
Concentration wave packets Microdomains
Structural description of <1 ½ 0> Ordering
Isostructural
microdomains
SRO <1 ½ 0> LRO 1/5 <420>
Different from SRO intensifying to become LRO
Multiple microdomains
Disordered matrix
Outline
•Ordering – chemical, magnetic, & electric• Evolution of Ordering• Competing superlattices in Ni4Mo alloy• Influence of radiation on order disorder• Order evolution
-- under electron irradiation
-- under heavy ion irradiationComparison of electron and ion irradiation results
Conclusions
Outline
•Ordering – chemical, magnetic, & electric• Evolution of Ordering• Competing superlattices in Ni4Mo alloy• Influence of radiation on order disorder• Order evolution
-- under electron irradiation
-- under heavy ion irradiationComparison of electron and ion irradiation results
Conclusions
Evolution of Order in Ni4Mo under electron Irradiation
170 K 473 K
Disordering of LRO state Persistence of 1½ 0 order (SRO) in initial SRO state
Evolution of Order in Ni4Mo under electron Irradiation
Damage rate: 10—3 dpa/s<1 ½ 0> & 1/5 <420> diffraction spotsremain linked during evolutionary stages S Banerjee, K Urban, M. Wilkens
Acta Met., 32 (1984) 299
Ordering Mechanisms Maps for Ni4Mo under e- irradiation
A: Destruction of LRO
B: No significant change of order for S=0, S=1
C: Continuous ordering by decay of <1 ½ 0>
waves & simultaneous amplification of LRO
D: Initially as in region C, after <1 ½ 0> disappear,
D1a domains nucleate & grow
E: Nucleation & growth of D1a
F: Destruction of <1 ½ 0>
G: <1 ½ 0> order decays at T > 550 K
H: <1 ½ 0> grows
I: Destruction of <1 ½ 0> & transition to LRO
S Banerjee, K Urban, M. Wilkens Acta Met., 32 (1984) 299
No LRO state below 450 K
No SRO State below 200 K
Ordering & Disordering Jumps
kT/
2
UEexp m0
VBVB
VAVA
Asymmetric energy barrier for vacancy-atom Interchange in ordered alloy
BABAt
CCkCCkdt
dS
VV
VV
CZCZ
CZCZk
Order-parameter vs. temperature plots- equilibrium condition- steady state condition under irradiation
Comparison between theory & experiment
equilibrium Under irradiation
S. Banerjee, K. Urban, Phys. Stat. Sol., 81, (1984) 145
Outline
•Ordering – chemical, magnetic, & electric• Evolution of Ordering• Competing superlattices in Ni4Mo alloy• Influence of radiation on order disorder• Order evolution
-- under electron irradiation
-- under heavy ion irradiationComparison of electron and ion irradiation results
Conclusions
Displacement cascades produced by 60 keV Au++ ions in ordered Ni4 Mo (D1a)
Black-white contrast From Dislocation loops (g = 200)
Disordered zones images withSuperlattice reflection (g = 1/5 <420>
M. Sundararaman, S. Banerjee, H. Wollenberger, Acta Met., 43, (1995) 107
Evolution of Order in Ni4Mo under ion Irradiation
Decay of LRO and gradual development of SRO intensity
300 keV Ni+ ;
Irradiation temperature - 600 K
Dose rate - 10-3 dpa/s
Evolution of Order in Ni4Mo under ion Irradiation
Development of SRO in the initially SRO and LRO specimens
i-SRO
i-LRO
Evolution of order in Ni4Mo under ion Irradiation
Final steady states at different irradiation temperatures
i-SRO
i-LRO
Steady state structures in Ni4Mo under ion irradiation
Initial state Domains Transitions <1 ½ 0> A <1 ½ 0> disappears B <1 ½ 0> decays C <1 ½ 0> grows D experimentally inaccessible 1/5 <420> E 1/5 <420> decays & <1 ½ 0> grows F 1/5 <420> persists
Cascade dynamics
Displacement cascade – 10-13 s
Thermal spike – 10-11 s
Final order decided by disordering and reordering within thermal spike
Quenching of thermal spike
- Amorphous
- Complete disorder
- Partial Order
Net vacancy concentration inside the cascade
By diffusion to periphery form loops around cascade
Substrate / sample temperature / thermal conductivity
Comparison between electron & ion irradiation
Steady state structures developed during e- and ion irradiation
Stochastic potential for maximum order versus T
Experiment Theory
Lower bound for LRO stability matches with experiment for e- irradiation
Conclusions
Distinct stability regimes for the CDO, the SRO and the LRO states could be obtained for electron and ion irradiation
Cascade effect decreases the temperature range of stability of LRO state while increases the temperature range of stability of SRO state
For electron irradiation, mixed state (SRO and LRO) can co-exist between 450 K and 800 K. No mixed state exist for ion irradiation
Low temperature for stability of LRO calculated by Kinetic and stochastic models match with experimental observation for electron irradiation
Acknowledgments
Dr. U.D. Kulkarni, BARC
Prof. K. Urban, KFA, Jülich
Prof. H. Wollenberger, HMI, Berlin
SIISVrVrIVSI
StVStVtVVIrVSV
StVStVtVVIrVSV
CCK)CK̂CK(C)CZ1(Pdt
dC
C)CC(K)CC(K)CC(KCCK)CZ1(Pdt
dC
C)CC(K)CC(K)CC(KCCK)CZ1(Pdt
dC
Kinetics: Rate of Change of point-defect concentrations (Vacancy, V, & Interstitial, I)
Production transfer transfer Annihilation at sinksRecombination
, : sublattice sites
S. Banerjee, K. Urban, Phys. Stat. Sol., 81, (1984) 145
Radiation Effects in Solids
Radiation Enhanced / Induced Segregation
Radiation Enhanced / Induced Diffusion
Radiation Enhanced / Induced Phase Transformation
-Generation of new phases-vacancy ordered
Radiation Enhanced / Induced Redistribution
Irradiation induced processes
Disordering – temperature independent
Reordering - temperature dependent
Net effect decides the final structure
Radiation Induced Disorderinge-
v
e-
I
v
v
I
I
Ion
Replacement Collison
RandomRecombination
DisplacementCascade
M. Sundararaman, S. Banerjee, &H. Wollenberger, Acta Met., 43, (1995) 107
Stochastic treatment
Probability of exchange of atoms from one 420 plane to the another is used in stochastic treatment to derive potential similar to thermodynamic model
In the absence of irradiation the potential are free energy functional. Under irradiation they are no longer free energy functional
The steady state probability distribution under irradiation given by
P*irr(N) = P*irr(c) exp[’
’) = Stochastic potential
number of atomic sites in 420 plane
C = concentration of Mo in the plane
LRO or SRO
= order parameter