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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 by G. K. DEY Materials Science Division Bhabha Atomic Research Division Mumbai 400085 * email:msraman@apsara.barc.ernet.in

2 Outline Ordering – chemical, magnetic, & electric Evolution of Ordering Competing superlattices in Ni 4 Mo alloy Influence of radiation on order  disorder Order evolution -- under electron irradiation -- under heavy ion irradiation  Comparison of electron and ion irradiation results Conclusions

3 Ordering – Chemical, ferromagnetic, ferroelectric Chemical Ordering Ferromagnetic Ferroelectric Ordering Empty lattice Atoms A & B Electric/ magnetic moments

4 Outline Ordering – chemical, magnetic, & electric Evolution of Ordering Competing superlattices in Ni 4 Mo alloy Influence of radiation on order  disorder Order evolution -- under electron irradiation -- under heavy ion irradiation  Comparison of electron and ion irradiation results Conclusions

5 Evolution of order Nucleation and Growth Continuous Ordering Order evolution could be either first or second order

6 Evolution of Ordering: Discrete Mode (Nucleation & Growth) Nucleation Disordered Matrix

7 Evolution of Ordering – Static Concentration Waves Single Variant K vector – B2 Ordering 3 variants K vector – L1 2 ordering

8 Continuous Ordering Amplification of concentration wave with time

9 First & second order transitions: Thermodynamic viewpoint n th order transformation: F E CpCp Temperature  First Order Second order

10 Energy barrier Nucleation & growth First & second order transitions: Landau Plots First Order (Discrete) Second order (Continuous)

11 Outline Ordering – chemical, magnetic, & electric Evolution of Ordering Competing superlattices in Ni 4 Mo alloy Influence of radiation on order  disorder Order evolution -- under electron irradiation -- under heavy ion irradiation  Comparison of electron and ion irradiation results Conclusions

12 Ordered States in Ni 4 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

13 Description of LRO and SRO structures [001] Projection LRO state SRO state p = 0,1,2,3 for modulation p = 0,1,2,3, 4 for 1/5 modulation

14 Concentration wave packets Microdomains Structural description of Ordering Isostructural microdomains SRO LRO 1/5 Different from SRO intensifying to become LRO Multiple microdomains Disordered matrix

15 Outline Ordering – chemical, magnetic, & electric Evolution of Ordering Competing superlattices in Ni 4 Mo alloy Influence of radiation on order  disorder Order evolution -- under electron irradiation -- under heavy ion irradiation  Comparison of electron and ion irradiation results Conclusions

16 Outline Ordering – chemical, magnetic, & electric Evolution of Ordering Competing superlattices in Ni 4 Mo alloy Influence of radiation on order  disorder Order evolution -- under electron irradiation -- under heavy ion irradiation  Comparison of electron and ion irradiation results Conclusions

17 Electron Irradiation Results 1 MeV electrons Dose rate = 10-3 dpa/s

18 Evolution of Order in Ni 4 Mo under electron Irradiation 170 K 473 K Disordering of LRO statePersistence of 1½ 0 order (SRO) in initial SRO state

19 Evolution of Order in Ni 4 Mo under electron Irradiation Damage rate: 10 —3 dpa/s & 1/5 diffraction spots remain linked during evolutionary stages S Banerjee, K Urban, M. Wilkens Acta Met., 32 (1984) 299

20 Ordering Mechanisms Maps for Ni 4 Mo under e - irradiation A: Destruction of LRO B: No significant change of order for S=0, S=1 C: Continuous ordering by decay of waves & simultaneous amplification of LRO D: Initially as in region C, after disappear, D1a domains nucleate & grow E: Nucleation & growth of D1a F: Destruction of G: order decays at T > 550 K H: grows I: Destruction of & 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

21 Ordering & Disordering Jumps Asymmetric energy barrier for vacancy-atom Interchange in ordered alloy

22 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

23 Outline Ordering – chemical, magnetic, & electric Evolution of Ordering Competing superlattices in Ni 4 Mo alloy Influence of radiation on order  disorder Order evolution -- under electron irradiation -- under heavy ion irradiation  Comparison of electron and ion irradiation results Conclusions

24 Ion Irradiation Results 300 keV Ni+ ions Dose rate = 10 -3 dpa/s

25 Displacement cascades produced by 60 keV Au++ ions in ordered Ni 4 Mo (D1a) Black-white contrast From Dislocation loops (g = 200) Disordered zones images with Superlattice reflection (g = 1/5 M. Sundararaman, S. Banerjee, H. Wollenberger, Acta Met., 43, (1995) 107

26 Evolution of Order in Ni 4 Mo under ion Irradiation Gradual decay of SRO and LRO states to CDO state

27 Evolution of Order in Ni 4 Mo 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

28 Evolution of Order in Ni 4 Mo under ion Irradiation Development of SRO in the initially SRO and LRO specimens i-SRO i-LRO

29 Evolution of order in Ni 4 Mo under ion Irradiation Final steady states at different irradiation temperatures i-SRO i-LRO

30 Loop size greater than 10 nm Dislocation loops in irradiated Ni 4 Mo;T = 900  C Frank loops

31 Steady state structures in Ni 4 Mo under ion irradiation Initial state Domains Transitions A disappears B decays C grows D experimentally inaccessible 1/5 E 1/5 decays & grows F 1/5 persists

32 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

33 Comparison of electron and ion irradiation results

34 Comparison between electron & ion irradiation Steady state structures developed during e- and ion irradiation Stochastic potential for maximum order versus T ExperimentTheory Lower bound for LRO stability matches with experiment for e - irradiation

35 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

36 Acknowledgments Dr. U.D. Kulkarni, BARC Prof. K. Urban, KFA, Jülich Prof. H. Wollenberger, HMI, Berlin

37 Thank you

38 Reaction kinetics model

39 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

40 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

41 Irradiation induced processes Disordering – temperature independent Reordering - temperature dependent Net effect decides the final structure

42 Radiation Induced Disordering e-e- v e-e- I v v I I Ion Replacement Collison Random Recombination Displacement Cascade M. Sundararaman, S. Banerjee, & H. Wollenberger, Acta Met., 43, (1995) 107

43 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

44 Stochastic treatment of ordering in Ni 4 Mo under electron irradiation CDO to SRO / LRO Lower critical temperature CDO to SRO / LRO Upper critical temperature Bellon and Martin, Phy. Rev. B39, (1988)

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