A COMPARISON OF THE ELECTRON AND ION IRRADIATION EFFECTS ON THE STABILITY RANGE OF ORDERED STRUCTURES IN Ni 4 Mo M. SUNDARARAMAN* and S. BANERJEE Presented

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




Conclusions

Evolution of order

Nucleation and Growth

Continuous Ordering

Order evolution could be either first or second order

Evolution of Ordering: Discrete Mode (Nucleation & Growth)

Nucleation

DisorderedMatrix

Evolution of Ordering – Static Concentration Waves

Single Variant <100> K vector – B2 Ordering

3 variants <100> K vector

– L12 ordering

Continuous Ordering

Amplification of concentration wave with time

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




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




Conclusions

Outline




Conclusions

Electron Irradiation Results

1 MeV electrons

Dose rate = 10-3 dpa/s

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




Conclusions

Ion Irradiation Results

300 keV Ni+ ions

Dose rate = 10-3 dpa/s

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

Gradual decay of SRO and LRO states to CDO state


Decay of LRO and gradual development of SRO intensity

300 keV Ni+ ;

Irradiation temperature - 600 K

Dose rate - 10-3 dpa/s


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

Loop size greater than 10 nm

Dislocation loops in irradiated Ni4Mo;T = 900 C

Frank loops

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 of electron and ion irradiation results

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

Thank you

Reaction kinetics model

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

Stochastic treatment of ordering in Ni4Mo under electron irradiation

CDO to SRO / LRO

Lower critical temperature

CDO to SRO / LRO

Upper critical temperature

Bellon and Martin, Phy. Rev. B39, (1988)

Documents

A COMPARISON OF THE ELECTRON AND ION IRRADIATION EFFECTS ON THE STABILITY RANGE OF ORDERED STRUCTURES IN Ni 4 Mo M. SUNDARARAMAN* and S. BANERJEE Presented