October 3, Small-Angle Neutron Scattering in Materials Science 1 Nuclear Physics Institute and Research Centre Řež near Prague, Czech Republic 2 IfW, TU Braunschweig, Germany 3 Helmholtz-Zentrum Berlin, Germany 4 TU München, Forschungsneutronenquelle Heinz Maier-Leibnitz, Garching, Germany 5 ILL Grenoble, France P. Strunz 1, D. Mukherji 2, G. Schumacher 3, R. Gilles 4 and A. Wiedenmann 5 Outline: n SANS and its applications to materials science n Examples –DT706 superalloy –core-shell nanoparticles –Porosity in thermal barrier coating Projects supported by the European Commission under the 6th Framework Programme through the Key Action: Strengthening the European Research Area, Research Infrastructures. Contract n°: RII3-CT '

October 3, Small-Angle Neutron Scattering n morphology n size n distance n orientation n volume fract. Scattering Length Density ρ( r ) Q : Scattering vector (momentum transfer) magnitude Q roughly proportional to the scattering angle Scattering curve. Evaluation: 2 –coherent elastic scattering on inhomogeneities of the size ≈ interatomic distances (i.e. 10 Å - 2  m) to small angles (up to 15°) Scattering contrast ( Δ ρ) 2

October 3, Small-Angle Neutron Scattering – data analysis n morphology n size n distance n orientation n volume fraction or

October 3, Properties of neutron n thermal neutrons: wavelength 1.8 Å (0.18 nm) and to velocity 2200 m/s n cold neutrons: typically 9 Å and 437 m/s n no charge, weak interaction with matter n magnetic moment n non-monotonic dependence of scattering amplitude on at. number (and even isotop) Why investigation of matter using neutrons? n interatomic distances and sizes of nanostructures in condensed matter similar to wavelength n often very small absorption => large depths (typically mm), volumes, in situ studies n study of magnetic structures n isotopic contrast variation, determination of “light” and “neighboring” elements

October 3, Applications: What can be investigated? n solid state physics - microstructure –Alloys, ceramics, glasses –Porosity, voids, microcracks –Semipermeable membranes –Porosity in ceramics –Phase transformations –Precipitates in metals, inclusions –Precipitate formation/dissolution in alloys –Nanoscaled materials, nanoparticles –Interfaces and surfaces of catalysts –Impurities in silicon n structural biology (biological macromolecules) –structure of biological macromolecular complexes e.g. DNA, protein, viruses; labeled subunits; multiprotein complexes; stoichiometry of interactions, molecular weights; lipids. n chemistry and mesoscopic systems –colloids; micelle systems and microemulsions; polymers; membranes; gels n magnetism –Magnetic/non-magnetic inhomogeneities –Ferofluids –Flux line lattices in superconductors  sample environment –orientation and deformation by shear flow –experiments under high pressure –magnetic field, electric field –mechanical load –high/low temperatures –adsorption facilities n any structural, compositional or magnetic particle/inhomogeneity/ microstructural entity with size 1nm-2μm giving scattering contrast

October 3, SANS  experimental technique Pin-hole facility Typical range Q:(0.001 – 0.3) Å -1 D:( ) Å SANS II facility of SINQ, Paul- Scherrer Institute (PSI) Villigen, Switzerland neutron guide sampleexchangable diaphragms detector velocity selector Beam-stop Vacuum chambers neutron guides

October 3, Use neutrons (SANS) when: n 1) bulk information or non-destructive testing is needed n 2) sample cannot be prepared in the thin form necessary for synchrotron without influencing the microstructure n 3) absorption/scattering in sample-environment windows too high for X-ray (in-situ experiments at extreme conditions) n 4) scattering contrast for X-ray too low or does not allow to resolve details (easier contrast variation for neutrons) n 5) magnetic microstructure B q  in D 2 Oin H 2 O Contrast variation

October 3, SANS  magnetic scattering Example of formula: scattering on homogenneous feromagnetic particle (M(r) = const.), polarized neutrons Δ  N... nuclear contrast Δ  M... magnetic contrast F(Q)... common formfaktor V P... volume of one particle c P... volume fraction ... Angle between Q a M P... beam polarization B Q  isotropic component component modulated by sin 2  B Application: voids and precipitates in ferromagnetic alloys radiation damage of reactor vessel steels ferrofluids flux lines in superconductors...

October 3, Vortex lattice in type-II superconductors Higher magnetic field => field penetrates, flux is quantized into tubes Generally: vortices move => resistance Zero resistance <= enough flaws to "pin" the vortices: vortex lattice (2D) Nature of vortex lattice and role of pinning: investigation also by SANS Higher magnetic field => field penetrates, flux is quantized into tubes Generally: vortices move => resistance Zero resistance <= enough flaws to "pin" the vortices: vortex lattice (2D) Nature of vortex lattice and role of pinning: investigation also by SANS R. Gilardi et al.: Small Angle Neutron Scattering Study of Vortex Pinning in High-T c Superconductor (La 2−x Sr x CuO 4 (x=0.17, T c =37 K). SINQ - experimental reports K. Harada et al., Hitachi Lab, Science 274, 1167 (1996)

October 3, Ni-base superalloys n Composition: e.g. Cr 8.0, Co 4.0, Mo 0.5, Al 5.7, W 9.0, Ti 0.7, Ta 5.7, Ni balance; in wt% n High creep resistance n High-temperature applications n Two-phase microstructure: –  -phase matrix strengthened by  ’ precipitates (size nm-  m) –optimized by heat treatment –essential for mechanical properties n 1. superallos are used at high- temperatures n 2. they are processed before the use at HT n => investigation of HT microstructure

October 3, size distribution (volume weighted) SCA433 5b1/4 HT experiment melting point: 1350°C

October 3, In-situ SANS investigation of high- temperature precipitate morphology in polycrystalline Ni-base superalloy DT706 new development of Ni-base superalloys: - improving their microstructural stability - preserving their good mechanical properties => Need to know the microstructure during heat treatment => the use of (in-situ) SANS D. Mukherji, D. Del Genovese, P. Strunz, R. Gilles, A. Wiedenmann and J. Rösler J. Phys.: Condens. Matter 20 (2008), (9pp)

October 3, Ex-situ treated samples DT706, SANS n We can model well the data => in- situ behavior can be well assessed Volume fraction 5%20%13%24%

October 3, DT706: in-situ SANS (HT furnace) Aim: Cooling rate (from solution treatment temperature) influence on precipitate microstructure Model: η andγ’

October 3, Size (γ‘) Integral intensity: determination at which temperature η and γ’ start to precipitate

October 3, Volume fraction increase in η at γ’ expense EM supports this observation 0.5 K/min outcome n Evolution of size and volume fraction for various cooling rates. γ’ size can be tuned using the in situ SANS results n start temperature of both η and γ’ determined n indication of growth of η at expense of γ’

October 3, Study of Ni 3 Si-type core-shell nanoparticles by contrast variation in SANS experiment Ni-Si alloy after two different heat treatments. P. Strunz, D. Mukherji, G. Pigozzi, R. Gilles, T. Geue, K. Pranzas Appl. Phys. A 88 [Materials Science & Processing], (2007) electrochemical selective phase dissolution

October 3, Extraction process TU Braunschweig and ETH Zurich  Ni–Si or Ni–Si–Al alloys: Ni 3 Si particles covered by amorphous shell made of SiO x  bio-resistant => may be suitable for medical application  Ni–Si or Ni–Si–Al alloys: Ni 3 Si particles covered by amorphous shell made of SiO x  bio-resistant => may be suitable for medical application  1. Formation of nano-sized precipitates structure in bulk alloy by heat treatment  2. Separating the nano- structure from the bulk: selective phase dissolution  3. Collection of nano-particles (ultrasound vibrations) shell:

October 3, Shell formation Possibilities :  1. Depletion of Ni from Ni-Si solid solution matrix and re-deposition of Si on particle surface;  2. Depletion of Ni from Ni 3 Si precipitate surface. Possibilities :  1. Depletion of Ni from Ni-Si solid solution matrix and re-deposition of Si on particle surface;  2. Depletion of Ni from Ni 3 Si precipitate surface. SANS: motivation  confirm core-shell structure by an independent method  indicate which mechanism of shell formation takes place  confirm core-shell structure by an independent method  indicate which mechanism of shell formation takes place  comparison: precipitates in the bulk alloy and nanoparticles  contrast variation (masking the shell)  comparison: precipitates in the bulk alloy and nanoparticles  contrast variation (masking the shell) method

October 3, Solid sample of Ni-13.3Si-2Al alloy  The inter-particle interference peak at low Q magnitudes: dense population of precipitates  four precipitate populations necessary to describe the data  The inter-particle interference peak at low Q magnitudes: dense population of precipitates  four precipitate populations necessary to describe the data  model: polydisperse 3D system of particles  2nd population: an extension of the 1st one  3rd and 4th populations in the channels between the larger precipitates  model: polydisperse 3D system of particles  2nd population: an extension of the 1st one  3rd and 4th populations in the channels between the larger precipitates  Polycrystalline alloy => isotropic => 3D cross section averaged grey: precipitate white: matrix 1 st population 2 nd population 3 rd population4 th population

October 3, nanopowder sample, contrast variation  extracted nanoparticles dispersed in various mixtures of H 2 O/D 2 O  all mixtures except 80% D 2 O: the slope at medium-to-large Q deviates from Porod law  evolution with changing SLD cannot be explained without the presence of a shell  extracted nanoparticles dispersed in various mixtures of H 2 O/D 2 O  all mixtures except 80% D 2 O: the slope at medium-to-large Q deviates from Porod law  evolution with changing SLD cannot be explained without the presence of a shell SLD of the shell: 49×10 9 cm −2 1 st population 2 nd population detail  model 80% D 2 O 100% D 2 O

October 3, comparison: precipitates vs. nanopowder comparison: precipitates vs. nanopowder  1st and 2nd distributions (core) correspond well in size scale with the original populations in the solid sample  => indication that the particle core was not attacked by the electrolyte during extraction process  1st and 2nd distributions (core) correspond well in size scale with the original populations in the solid sample  => indication that the particle core was not attacked by the electrolyte during extraction process  distributions in solid sample compared to extracted nanoparticles  displayed distributions:  the core and  the core + shell  distributions in solid sample compared to extracted nanoparticles  displayed distributions:  the core and  the core + shell

October 3, In-situ SANS Study of Pore Microstructure in YSZ Thermal Barrier Coatings P. Strunz, G.Schumacher, R. Vassen and A. Wiedenmann, Acta Materialia, Vol 52/11, 2004, pp

October 3, Ceramic Thermal Barrier Coatings n Preparation: –Air Plasma Spraying (APS), –Electron Beam Physical Vapor Deposition (EB PVD) n highly porous material, pore microstructure determines properties

October 3, n 1. large pores and cracks (radius > 100 nm) n 2. medium-size pores (~20 nm) n 3. nanometric pores (1-10nm) TBC: samples (set 47) treated ex-situ at 1200ºC n No thermal exposure: –hydrogen? –extremely small pores? –combination? for 0, 1, 10 and 100 hours Model:

October 3, in situ: creation of nanopores n from ex-situ: there are nanopores after 1h at 1200 ºC n => created between 400 and 1200ºC n nanopores created at 800ºC

October 3, ZrO 2 TBC (plasma sprayed): nanometric pores n in- and ex- situ measuremen t fit well together n 800ºC: population of nm- sized pores created. n between 800°C and 1200ºC, this population is unchanged n annealing at 1200ºC: size increases, volume decreases

October 3, Applications (not exhaustive list): n solid state physics - microstructure –Alloys, ceramics, glasses –Porosity, voids, microcracks –Semipermeable membranes –Porosity in ceramics –Phase transformations –Precipitates in metals, inclusions –Precipitate formation/dissolution in alloys –Nanoscaled materials, nanoparticles –Interfaces and surfaces of catalysts –Impurities in silicon n magnetism –Magnetic/non-magnetic inhomogeneities –Ferofluids –Flux line lattices in superconductors n 1) bulk information or non-destructive testing is needed n 2) sample: cannot be prepared in the thin form necessary for synchrotron without influencing the microstructure n 3) absorption/scattering in sample-environment windows too high for X-ray (in-situ experiments at extreme conditions) n 4) scattering contrast for X-ray too low or does not allow to resolve details (easier contrast variation for neutrons) n 5) magnetic microstructure What can be determined? n Average particle size n Surface area (I ~ S/Q 4 ) n Volume fraction n Particle shape n Internal structure (contrast variation) n Size distributions SAS in solid state physics: use neutrons when