Vyacheslav Em

Effect of wavelength-dependent attenuation on neutron diffraction stress measurements at depth in steels

The wavelength dependence of the maximum feasible penetration depth was studied for neutron diffraction stress measurements in ferritic and austenitic steels. This property was examined with wavelengths from the close vicinity of the Bragg edges, where the neutron total cross section has its local minimum and for which the scattering angles are convenient for stress measurements. These wavelengths (e.g. 2.39 and 2.19 A) are longer than those commonly used in stress measurements (∼1.6 A). By using such wavelengths, configured by a focusing bent perfect crystal Si(111) monochromator, it was observed that the available total beam path length is about 85 mm in both ferritic and austenitic steels. This study provides specific information for choosing the instrument configuration suitable for most strain-scanning experimental tasks.

Study of decomposition and reactions with aluminum matrix of dispersed atomized U-10 wt% Mo alloy

Abstract A neutron diffraction study of atomized U-10 wt% Mo alloy showed that homogenizing annealing above 560 °C retards the decomposition of the metastable γ-phase at 400 and 500 °C. In fuel with U-10 wt% Mo alloy particles dispersed in the Al matrix, Al diffuses along the grain boundaries and reacts with α-U phase formed from the decomposed γ-phase at 400 and 500 °C. The formation of Al3U and Al2U phases was observed. Neutron diffraction did not detect formation of a ternary Al–U–Mo compound.

Neutron diffraction study of U–5.4 wt% Mo alloy

Abstract The structure of U–5.4 wt% Mo alloy prepared by the centrifugal atomization method and the decomposition of the alloy at elevated temperature were studied. The single uniform γ-phase was obtained after annealing the synthesized alloy at 700°C for 48 h. The homogenized alloy was annealed at 400°C and 500°C to search for an ordered phase and study the decomposition process. No ordered phase in U–5.4 wt% Mo alloy after annealing was observed. With the result from the Rietveld refinement of the neutron diffraction patterns it was concluded that the b parameter of the α-phase is contracted like metastable α′-phase and phase boundary of the α-phase region at 500°C lies near 2.6 at.% Mo.

Optimization of a bent perfect Si(111) monochromator at a small take‐off angle for use in a stress instrument

The reflectivity and resolution properties of focusing cylindrically bent perfect crystal Si(111) monochromators of different diffraction geometries were tested with the aim of evaluating their possible use in a stress instrument with an unusually small take-off angle (2θM ≃ 30°). The experiments showed that an Si crystal with reflecting planes (111) in the symmetric diffraction geometry provides a maximum figure of merit for accuracy in the peak position that is comparable to that achieved previously from an optimized Si(220) monochromator at 2θM ≃ 55°.

Growth and Characterization of Gallium-Doped ZnO Films for α-Particle Scintillators

Gallium-doped ZnO (ZnO:Ga) films for an α-particle scintillator were grown on a sapphire (0001) substrate by radio-frequency magnetron sputtering. Spectral analysis shows that the photoluminescence and scintillation properties of ZnO:Ga films under α-particle radiation can be remarkably improved by a post rapid thermal annealing process and also by increasing the film thickness. The surface morphology, crystallinity, and scintillation properties of ZnO:Ga thin films were further improved by in situ growth interruption during the two-step growth process.

Residual stress determination in thick welded steel plates

Through thickness strain distribution of 50 mm thick welded ferritic steel (bcc) plate was studied using diffraction reflections 211 and 110 and neutron wavelengths of 1.55 and 2.39A, respectively. Experimental results showed that for stress measurements in a possibly maximum thick weld, the different strain components should be measured with different reflections 211 and 110. The strains measured with these reflections for the same component are close. Since planes (211) and (110) of bcc ferrite have the same diffraction elastic constants the appropriate values of stresses could be derived from strains measured with reflections 211 and 110.

Experimental studies of dispersive double reflections excited in cylindrically bent perfect-crystal slabs at a constant neutron wavelength

Multiple Bragg reflections (MBRs), which can be realized in a bent perfect crystal (BPC) slab and are mutually in dispersive diffraction geometry, provide a monochromatic beam of excellent resolution. After identifying many MBR effects in a BPC Si crystal by using the method of θ–2θD scanning, we have turned our attention to the study of selected effects using the method of azimuthal rotation of the crystal lattice around the scattering vector of the primary reflection for a fixed chosen wavelength. In this paper, several azimuthal scans with the intention of possible practical exploitation for very high resolution diffractometry are presented.

In Situ Neutron Diffraction Measurements of the Deformation Behavior in High Manganese Steels

Deformation behavior of high Mn TWIP (twinning induced plasticity) steels was observed using neutron diffraction. Two kinds of specimens were prepared; 0 and 2 wt% of Al TWIP steels. The lattice strains and peak widths of hkl grains were measured under tensile loading. The results provide an insight into the influence of the Al contents on the deformation behavior associated with the microstructure changes in TWIP steels.

Unconventional Performance of a Highly Luminous Strain/Stress Scanner for High Resolution Studies

In this paper properties of the dedicated neutron strain/stress diffractometer installed at the beam port ST-1 of HANARO reactor in KAERI which has been optimized at a small monochromator take-off angle, are described. Thanks to the employment of the horizontally focusing bent perfect crystal monochromator and the optimization procedure good resolution can be achieved and namely, the luminosity of the instrument can be considerably increased which permits us to enlarge the range of the material depth for residual strain/stress mapping. Moreover, new alternative of the diffractometer permits also to investigate some kinetic processes in polycrystalline materials running within few seconds.

Residual Stress Measurements Through the Thickness of the Dissimilar Weld Pipe Using Neutron Diffraction

The distribution of residual stresses was determined in an overlay dissimilar joining pipe weld using neutron diffraction. The specimen was dissimilarly welded between the bcc ferrite steel (SA508) and fcc austenite (SA182) steel with the Ni-based welding consumable (Alloy 182). The weld pipe simulates the nozzle joint component of the nuclear power plants with the dimension of about 130-mm diameter, 500-mm length, and 21-mm thickness. A total of 13 positions were measured from 2 mm to 20 mm underneath the pipe outer wall with 1∼2 mm steps along the weld centerline. The neutron beam gauge volume provides 1-mm spatial resolution along the thickness direction of the weld pipe. The macroscopic ‘stress-free’ lattice spacing (do) was also measured using 2-mm width comb teeth coupons taken from the identical location of the bulk weld neutron-diffraction measurements. The result shows that the hoop stress component developed tension of about 100 MPa and compression of −600 MPa near the outer and inner wall surface of the overlay pipe weld, respectively.Copyright