Gizo Bokuchava

1. Frank Laboratory of Neutron Physics Joint Institute for Nuclear Research Neutron Fourier Diffractometer FSD for Residual Stress Studiesin Advanced Materials and Industrial Components GizoBokuchava STI 2011, June 6-9, Dubna

2. a/a0= (d – d0)/d0- peak shift (macro-stress) Bragg law: 2dexpsin =  d = tμs/(505.556 Lmsin) (TOF-method) Diffraction experiment for measuring of internal stresses inside material or component incident neutron beam Peak shift under applied load diaphragm gauge volume sample By two detectors at 90 one can measure stresses in both Q1 and Q2 directions simultaneously Peak shift for steel sample (E=200 Gpa) at stress value of 20 MPa and 200 MPa

3. Diffraction peak broadening effects W2 = W02 + C1d2 + C2d4 – diffraction peak width C1 = <ε>2– variance of d (microstrain) C2~ 1/<D>2– crystallite size W0– instrument resolution function Peak broadening due to microstrain. Estimated microstrain value: e=0.012±0.004 (Sample 1) e=0.0100.004 (Sample 2) Resolution function (standard Al2O3 sample) andpeak broadening effect due to crystallite size (dispersiveNi).

4. IBR-2 pulsed reactor IBR-2 Spectrometers Courtesy of J.Emelina

5. High-resolution Fourier diffractometry for long pulse neutron source IBR-2 is a long-pulse neutron source. Δt≈300 μs, R ≈ 0.01 (L=25 m, d=2 Å) Objective: R ≤ 0.001 (L=25 m, d=2 Å) Fast Fourier chopper F-chopper parameters (FSD): N=1024 Vmax=6000 rpm Ωmax=100 KHz Δt0≈10 μs

6. Fourier chopper Slit width 0.7 mm Stator Rotor Transmission function Binary signals Schematic diagram of the Fourier diffractometer 1. P.Hiismaki, Introduction of RTOF-method Neutron Inelastic Scattering, IAEA, Vienna, 1972, 803 2. The first realization of RTOF Fourier-method R.Heinonen, P.Hiismaki, A.Piirto et al, New Methods and Techniques in Neutron Diffraction, Report RCN-234, Petten, 1975, 347

7. Resolution of a TOF - diffractometer R(t, θ) = Δd/d = [(Δt0/t)2 + (Δθ/tgθ)2+2+d2/<D>2]1/2, t ~L·d·sinθ, R→0 if Δt0→0 or L→∞ and Δθ→0 or θ→π/2 FSD diffractometer, IBR-2 (RUSSIA) R(t) ≈∫g(ω)cos(ωt)dω, ΔR=Δt0≈ 1/Ωm=(Nωm)-1=(1024·100 kHz)-1≈10 μs For Δt0≈10 μs and L≈6.5 m: time component Δt0/t ≈ 2.5·10-3 ford=1 Å and 2=90

8. Resolution function (peak shape) R(t) ≈∫g(ω)cos(ωt)dω is Fourier transformation of g(ω). Ωm 0 g(ω) is frequency distribution (frequency window) Frequency window FSD: Blackman window g(u)=1 + p·cosπu + q·cos2πu where p=1.03, q=0.08, u=ω/ωmax

9. Simulation: RTOF data acquisition

10. FSD – Fourier Stress Diffractometer at the IBR-2 pulsed reactor (JINR, Dubna)

11. FSD diffractometer Backscattering detector Current status of the detector system : Three modules of ZnS(Ag) +90° (left) detector are installed on FSD. The similar three modules are installed on -90° (right) detector. 90º-detector Sample position Neutron guide

12. FSD detector system: combined geometrical and electronic focusing Interior arrangement of the single detector module Right bank of 90º-detector consists of 7 ZnS(Ag) based modules. Courtesy of Valery Kudryashov Flexible the scintillation screen allows each element of the detector to approximate the time focusing surface ofthe scattered neutrons with a necessary accuracy. At the same time, the electronics provides the adding up of signals from separate detector elements on a single TOF-scale. This combination leads to a sharp increase of the solid angle of the detector system and as a results, to an increase of its luminosity preserving high resolution d/d410-3.

13. FSD detector system: combined geometrical and electronic focusing • RTOF spectra focusing • Scale coefficients for each detector element: • ki=Lisin(i) / L0sin(0), • where L is flight path, • is scattering angle for i-th and • base detectors, correspondingly. E.S. Kuzmin, A.M. Balagurov, G.D. Bokuchava et al., J. of Neutron Research, Vol. 10, Number 1 (2002) 31-41

14. Radial collimator Single modules of the collimator Multisectional radial collimator Gauge volume = 2 mm, Number of slits = 160, Length = 600 mm, Focus distance = 350 mm Multisectional radial collimator system: 7° and 10° modules are installed

15. Measured spatial resolution function for radial collimator (FHWM2 mm) Sample surface scan with radial collimator Gauge volume definition: neutron intensity distribution map for radial collimator. Incident beam width ~10 mm Residual stress study by neutron diffraction within bulk sample using radial collimators

16. Measured spectra and resolution function FSD resolution function measured on -Fe powder at maximal Fourier chopper speed Vmax=6000 rpm Part of neutron diffraction pattern from the -Fe standard sample measured on FSD in high-resolution mode by BS- (top) and 90 (bottom) detectors. Experimental points, profile calculated by the Rietveld method and difference curve are shown.

17. Diffraction peak shape and pulse width Diffraction peak shape dependence versus maximal Fourier chopper speed Effective neutron pulse width dependence versus maximal Fourier chopper speed

18. FSD operation parameters Neutron guidemirror, Ni-covered Beam cross-section at exit 1075 mm2 Moderator – sample distance 28.14 m Chopper – sample distance 5.55 m Fourier - chopper (disk) high-strength Al based alloy outer diameter 540 mm slit width 0.7 mm number of slits 1024 max. rotation speed 6000 rpm max. modulation frequency 100 kHz Thermal neutron pulse width: low-resolution mode320 s high-resolution mode9.8 s Neutron detectors: Backscattering (2 = 141, 6Li) 2.310-3 ASTRA (2 = ±90, ZnS) 4.010-3 Wavelength interval 0.9 ÷ 8 Å Flux at sample position: without Fourier chopper1.8106 n/cm2/sec with Fourier chopper3.7105 n/cm2/sec

19. Sample environment 5 – axis HUBER goniometer ,-axis, x,y,z-table Investigated sample installed on “Huber” goniometer.

20. Sample environment Mirror furnace Two standard halogen lamps (output power of 1 kW) with a common focus at sample position provide a working temperature range up to 1000 C (can be upgraded up to 2000 C) and temperature stability of 0.2 C. The design of the furnace allows one to use wide range of neutron scattering angles: in the scattering plane - 360, in the vertical plane - 22.

21. Sample environment Stress rig ”TIRAtest”(Fmax=60 kN)

22. New stress rig LM-20 for FSD diffractometer (produced in NPI, Řež, Czech Republic) Force range - ±20 kN, temperature range - up to 800 ºС Steel sample with mechanical extensiometer Sample heating by direct current Typical samples Mechanical testing machine LM-20 during test experiments in FLNP JINR.

23. New SONIX+ instrument control system developed by Kirilov A.S., Murashkevich S.M., PetukhovaТ.B., Yudin V.E. (SONIX - SOftware for Neutron Instruments on X11 base) Sonix+ advantages: -GUI user friendly interface -flexible Python-based script language -simple data visualization -low cost

24. Four point bend experiment Sample x Four point bending devicewith test sample.Scan points are shown in blue Lattice strain vs X coordinate

25. Elastic lattice strain versus sample deformation in elastic region (up to ~0.004) Elastic lattice strain versus applied load. Sample Nr.4 undergoes plastic deformation Experimental values of Young‘s modulus for D16 Al alloy (russ. grading) Mean value <Е> = 68.62  0.82 GPa for D16 alloy

26. Further development • Additional elements for detector system; • - 2nd radial collimator; • - Sample environment improvement.

27. Conclusions • the obtained results show that the RTOF neutron diffraction method can be used for residual stress studies in various industrial components and new advanced materials; • - the achieved parameters of the FSD (high resolution, wide dhkl-range, high contrast of Fourier chopper, appropriate neutron intensity spectral distribution) allows one to study residual stresses with required accuracy. • - further expansion of the solid angle of the detector system (preserving a high resolution level d/d2.3÷410-3) will lead to a sharp increase of experiment effectiveness.

28. Thank you for attention!