Situneutron Diffraction Research Articles

Investigation of α-Ti plastic anisotropy under thermomechanical loadings: temperature influence on deformation mechanisms

In situneutron diffraction method has been used to investigate deformation mechanisms (slip and twinning deformation modes) during uniaxial tensile tests of extruded a-titanium alloy at room temperature, 100 and 300 °C. For this purpose, the prediction of an Elasto-Plastic Self-Consistent (EPSC) model was compared with the experimental data. Results show that there is a good agreement between the simulations and neutron diffraction measurements. The EPSC model enables realistic predictions of not only the elastic lattice strains developed in variously oriented grain families but also the macroscopic stress-strain response within the bulk material.

Single-pass flow-through reaction cell for high-temperature and high-pressurein situneutron diffraction studies of hydrothermal crystallization processes

A large-volume single-pass flow-through cell forin situneutron diffraction investigation of hydrothermal crystallization processes is reported. The cell is much more versatile than previous designs owing to the ability to control independently and precisely temperature (up to 673 K), pressure (up to 46 MPa), flow rate (0.01–10 ml min−1) and reaction-fluid volume (≥65 ml). Such versatility is realized by an innovative design consisting of a room-temperature and ambient-pressure external fluid supply module, a high-pressure reaction module which includes a high-temperature sample compartment enclosed in a vacuum furnace, and a room-temperature and high-pressure backpressure regulation module for pressure control. The cell provides a new avenue for studying various parameters of hydrothermal crystallizations independently,in situand in real time at extreme hydrothermal conditions (e.g.supercritical). The cell was successfully commissioned on the high-intensity powder diffractometer beamline, Wombat, at the Australian Nuclear Science and Technology Organisation by investigating the effect of pressure on the hydrothermal pseudomorphic conversion from SrSO4(celestine) to SrCO3(strontianite) at a constant temperature of 473 K and flow rate of 5 ml min−1. The results show that the increase of pressure exerts a nonlinear effect on the conversion rate, which first increases with increasing pressure from 14 to 20 MPa, and then decreases when pressure further increases to 24 MPa.

Neutron time-of-flight diffraction used to study aged duplex stainless steel at small and large deformation until sample fracture

Owing to its selectivity, diffraction is a powerful tool for analysing the mechanical behaviour of polycrystalline materials at the mesoscale (phase and/or grain scale).In situneutron diffraction during tensile tests and elastoplastic self-consistent modelling were used to study slip phenomena occurring on crystallographic planes at small and large deformation. The critical resolved shear stresses in both phases of duplex stainless steel were found for samples subjected to different thermal treatments. The evolution of grain loading was also determined by showing the large differences between stress concentration for grains in ferritic and austenitic phases. It was found that, for small loads applied to the sample, linear elastic deformation occurs in both phases. When the load increases, austenite starts to deform plastically, while ferrite remains in the elastic range. Finally, both phases undergo plastic deformation until sample fracture. By using an original calibration of diffraction data, the range of the study was extended to large sample deformation. As a result, mechanical effects that can be attributed to damage processes initiated in ferrite were observed.

A novel electrochemical cell forin situneutron diffraction studies of electrode materials for lithium-ion batteries

Lithium-ion batteries are based on the principle of intercalation of lithium ions in host materials, both at the anode and at the cathode. These materials are in general crystalline and, during the operation of the battery, they undergo numerous phase transitions and structural rearrangements, often amplified by the presence of an applied potential difference. Whilein situX-ray diffraction is an established technique in this field,in situneutron diffraction is still in its pioneering stages and only a few attempts have been made to design an electrochemical cell suitable for these experiments. The technical development of such a device, along with a discussion of its serviceability to combine electrochemical measurements with neutron diffraction experiments, is hereby presented.

Kinetic neutron diffraction study ofNb3Sn phase formation in superconducting wires

The kinetics of Nb3Sn phase formation in commercial multifilamentary wires have been studiedas a function of time and temperature using time-resolved, in situneutron diffraction. This work shows that at higher temperatures theNb3Sn phaseforms in a fraction of the recommended annealing time. A temperature-independent Avrami exponent ofn = 0.51 ± 0.01 wasobserved, indicating a diffusion-controlled growth mechanism, and a large apparent activation energyof Ea = 10 ± 1 eV is reported where the energies of nucleation and growth both contribute.

In situX-ray and neutron powder diffraction study of LaNi5-xSnx–H systems

ABSTRACTWe have studied structural change and lattice strain formation during absorption and desorption of hydrogen (deuterium) by high purity LaNi5-xSnxalloys (x= 0.22, 0.25) usingin situX-ray and neutron diffraction along with simultaneously measuring theP-Cisotherms. From profile analysis of the X-ray diffraction data, lattice parameter and lattice strain in each hydriding state are evaluated.In situneutron diffraction data provided hydrogen occupation changing with hydrogen content. Significant lattice contract and strain formation were observed in the hydride phase in desorption. This behavior was related with decrease in hydrogen occupation in the hydride phase revealed from the neutron diffraction data.

Elaboration, Structures, and Phase Transitions for YFe2DxCompounds (x=1.3, 1.75, 1.9, 2.6) Studied by Neutron Diffraction

The structure of YFe2Dxdeuterides (x=1.3, 1.9, 1.75, and 2.6) have been studied by neutron diffraction (ND). The influence of a thermal treatment on the synthesis of YFe2Dxdeuterides has been followed byin situneutron diffraction forx=1.3 and 1.9. After deuterium absorption at room temperature, their diffraction patterns show a mixture of YFe2and a deuteride phase YFe2Dy(2.3<y<2.6). Heating the samples above 400 K forx=1.3 and 425 K forx=1.9, leads to a deuterium diffusion from the deuterium rich phase toward YFe2to form a single phase deuteride with lower D content. Single phase deuterides YFe2D1.3, YFe2D1.75, and YFe2D1.9display superstructure lines which imply a lowering of symmetry compared to the cubic C15 structure of the parent intermetallic. YFe2D1.3crystallizes in the tetragonalI4space group (Z=20) witha=11.985(2) Å andc=7.622(1) Å, YFe2D1.75in the cubicI43mspace group (Z=64) witha=15.336(2) Å, and YFe2D1.9in a tetragonal structure witha=12.145(2) Å andc=23.064(2) Å. The analysis of their ND patterns at 300 K shows forx=1.3 and 1.75 an ordering of the deuterium atoms in some preferential tetrahedral Y2Fe2 sites and a ferromagnetic structure with 1.5 and 1.9μB/Fe, respectively. For YFe2D1.3and YFe2D1.9the superstructure lines disappear above 460 and 444 K, respectively, and they return to a C15 structure. The origin of the structural deviation and of the order–disorder transition is discussed in relation with deuterium and magnetic ordering. YFe2D2.6deuteride crystallizes at 300 K in the cubicFd3mspace group (Z=8) witha=7.785(2), deuterium atoms located statistically in tetrahedral Y2Fe2 sites and a ferromagnetic structure with a magnetic moment of 1.8μB/Fe.

A neutron diffraction cell for studying lithium-insertion processes in electrode materials

An electrochemical cell has been constructed forin situneutron diffraction studies of lithium-insertion/extraction processes in electrode materials for Li-ion batteries. Its key components are a Pyrex tube, gold plated on its inside, which functions as a current collector, and a central lithium rod, which serves as the negative electrode. The device is demonstrated here for a neutron diffraction study of lithium extraction from LiMn2O4: a mechanical Celgard©separator soaked in the electrolyte surrounds the lithium electrode. The LiMn2O4powder, mixed with electrolyte, occupies the space between separator and current collector.