Friday 12 July 2013, Moorfoot & Kilsyth Rooms, 11:00-13:00
Structural materials
In-situ bi-axial mechanical testing at POLDI@PSI
J Repper, M Niffenegger, S Van Petegem, W Wagner and H Van Swygenhoven
Paul Scherrer Institut, Switzerland
Complementary to uni-axial mechanical testing multi-axial tests allow studying the material response to complex
strain paths and/or multi-stage loading. Such conditions are typically present in the service environment of
industrial components as well as during their production process. Multi-axial testing is also important for validating
sophisticated material models, which predict the mechanical behaviour for complex loading conditions. Mechanical
testing combined with neutron diffraction provides information on the micro mechanical material behaviour during
deformation and thus, helps to better understand the macroscopic mechanical response.
In this contribution we present results of a first series of in-situ bi-axial tests performed at the neutron TOF
diffractometer POLDI. The intergranular strain evolution within cruciform stainless steel 316L samples will be
compared with the strain evolution obtained in-situ on uni-axial charged samples. The macroscopic strains were
monitored by a digital image correlation system.
In addition we present the new multi-axial mechanical test rig of POLDI. Beside uni-axial in-situ testing the modular
test machine set-up will allow in-situ tension/compression testing with neutrons on cruciform samples. The uni-axial
set-up is equipped with a torque actuator. A furnace for temperatures up to 1200°C is planned to be installed later.
The new in-situ test machine will be installed in Summer 2013.
Precipitate microstructure evolution in inconel superalloys
P Strunz1, M Petrenec2, U Gasser3, J Tobiáš2, J Polák2 and J Šaroun1
1
Nuclear Physics Institute ASCR Řež, Czech Republic, 2Institute of Physics of Materials ASCR Brno, Czech
Republic, 3PSI, Switzerland
The critical parts of turbines made of Ni-based superalloy are subjected to cyclic elastic-plastic straining as a result
of heating and cooling during start-up and shut-down periods. Consequently, low-cycle fatigue at operating
temperatures (up to 900°C) is an important factor in the evaluation of the service life.
Nickel base superalloy Inconel is a natural composite consisting of γ' precipitates (L12) with an ordered structure
coherently embedded in a γ solid solution (fcc) matrix. The thermo-mechanical exposure during low-cycle fatigue is
connected with a change of its microstructure, namely the size and distribution of precipitates.
The IN738LC and IN792 superalloys were studied by ex- and in-situ Small-Angle Neutron Scattering (SANS).
Additional precipitation occurs above 570°C with relatively slow kinetics. The precipitates are created at the
elevated temperatures nearly regardless the application of low-cycle fatigue. Nevertheless, these small precipitates
could influence the fatigue parameters, as indicated by the anomaly in the same temperature range. The small (up
to 10 nm at 700°C) precipitates were found (and confirmed with the help of high-resolution TEM) to be a third
population of γ´. The limits of the temperature range where the third γ´ population is produced were estimated
using SANS. The kinetics of precipitate size evolution during the hold at temperatures 700°C and 800°C were
determined.
ICNS 2013 International Conference on Neutron Scattering
(invited) Nonlinearity and isotope effect in temporal evolution of mesoscopic structure during hydration of cement
S Mazumder
Bhabha Atomic Research Centre, India
Though cement is a ubiquitous material, the mechanism of its hydration and evolution of cement-water mixtures
into gels of high compressive strength is poorly understood, despite extensive research over the past century.
Recent investigations [1-5], based on neutron scattering measurements, aims at unraveling this enigma and
outlines, for the first time, the evolution of the mesoscopic structure of the cement paste which exhibits temporal
oscillations, strongly dependent on the scale of observation and on the medium of hydration (light or heavy water).
While the formation of hydration products is synchronous for hydration with H2O, the process is non-synchronous for
hydration with D2O. The reason why morphological patterns of domains at different times look dissimilar, as seen
before (Phys. Rev. Lett. 93, 255704 (2004); Phys. Rev. B. 72, 224208 (2005)), for different hydration media
emerges as a natural consequence of this finding. The noteworthy observations point to the effect of hydrogen
bonding on mesoscopic structure resulting from hydration although hydrogen bond with deuterium is only slightly
stabler yielding a longer lifetime vis-a-vis bond involving hydrogen.
[1]
[2]
[3]
[4]
[5]
S. Mazumder, et al., Phys. Rev. Lett 93 (2004) 255704
S. Mazumder, et al., Phys. Rev. B 72 (2005) 224208
S. Mazumder, et al., Phys. Rev. B 76 (2007) 064205
S. Mazumder, et al., Phys. Rev. B 82 (2010) 064203
S. Mazumder, et al., Phys. Rev. B 84 (2011) 134302
Small angle neutron scattering study of ferritic oxide dispersion strengthened steel for future nuclear application
Y-S Han, X Mao, J Jang, T-H Kim
Korea Atomic Energy Research Institute, Korea
The nano sized microstructures in ferritic ODS(Oxide Dispersion Strengthened) steels for future nuclear application
were studied by SANS(Small Angle Neutron Scattering). The ferritic ODS steels were manufactured by HIP(Hot
Isostatic Pressing) with various chemical compositions and fabrication conditions. The SANS experiments were
performed by the 40 meter SANS instrument at HANARO. Due to the ferromagnetic nature of the ferrous alloys, the
horizontal magnetic field of 1 Tesla were applied during the SANS experiment. The nano sized microstructure such
as yttrium oxides and Cr-oxides were quantitatively analyzed by SANS. The yttrium oxides and Cr-oxides were also
observed by transmission electron microscopy. The microstructural analysis results from small- angle neutron
scattering were compared with those obtained by transmission electron microscopy. The effects of chemical
compositions and fabrication conditions on microstructure were investigated in relation to the quantitative analysis
results obtained by SANS. The ratio between magnetic and nuclear scattering components was calculated and the
characteristics of the non-magnetic nano sized microstructures in experimental ferritic ODS steels were discussed
from the SANS analysis results.
Temperature phase stability in gamma TiAl based alloys alloyed with Mo and/or C determined by neutron diffraction
P Beran1, M Petrenec2, M Heczko3, B Smetana4 and M Smid3
1
Nuclear Physics Institute ASCR, Czech Republic, 2TESCAN, Czech Republic, 3Institute of Physics of Materials, Czech
Republic, 4VŠB–Technical University of Ostrava, Czech Republic
During the last decade research activities have been focused to the development of TiAl alloys with high niobium
additions with the baseline composition Ti-44Al-7Nb (at.%) what show good combination of high creep strength,
good ductility at room temperature, improved fatigue properties and excellent oxidation resistance. However, their
ICNS 2013 International Conference on Neutron Scattering
applications are hindered by relatively low room temperature ductility, poor fracture toughness and bad hot
workability. One of effective ways to improve deformability (plasticity) of advanced gamma-TiAl-Nb alloys is via the
microstructure control by complex heat treatment. For developing the good heat treatment procedure one need to
know the phase diagram. So we adopt neutron powder diffraction technique to study the temperature phase
stability in different TiAl-Nb alloys doped by Mo and/or C. Mo increase in the base alloy the amount of beta-TiAl
phases what introduce the ductility and C increase the amount of alpha-Ti3Al phases what can introduce in lamellar
structure the strength. By comparing the neutron diffraction data with DSC (differential scanning calorimetry) curves
we were able to determine and separate the phase transformation and/or ordering/disordering temperatures what
will lead to develop optimal heat treatment for this kind functional materials and possibly develop the model for
future prediction of needed heat treatment depending wanted mechanical properties.
Evaluation of dislocation density as a function of strain rate and temperature using neutron diffraction
S Chandra, M Rao, M Samal, S Rawat, V Chavan, R Patel and S Chaplot
Bhabha Atomic Research Centre, India
Neutron Scattering using diffraction techniques is recognized as one of the most precise and reliable methods of
investigating dislocations in a deformed metal matrix. Such line defects, inherent to metals and alloys, are strongly
influenced by shock loading. These effects on the density of dislocations are still poorly investigated in the
literature, although in widely used materials these applications need knowledge of structure transformation under
shock loading.
Single crystal copper samples were compressed at high strain rates of the order of 2000/s at different
temperatures ranging from 300K-473K using Split Hopkinson Bar. The loading is applied in [100] and [011]
crystallographic directions resulting in substantial differences in the deformation pattern as well as mechanical
properties. Of special relevance to these measurements is the dislocation density measurement through Neutron
Diffractometry at DHRUVA reactor, BARC. The evolution of dislocation density as a function of strain rates and
temperature is investigated through these neutron diffraction experiments.
Numerical Simulations are also carried out through Molecular Dynamics and Crystal Plasticity Finite Element models
to investigate the evolution of dislocation density under shock loading. The measured values from the Neutron
Diffraction Experiments and Simulations are analyzed quantitatively and a conclusion on the correlation of
Dislocation Density as a function of Strain Rates and Temperature derived.
ICNS 2013 International Conference on Neutron Scattering