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

Multi-scale analyses of constituent phases in a trip-assisted duplex stainless steel by electron backscatter diffraction, in situ neutron diffraction, and energy selective neutron imaging

Micrometer to centimeter scale analyses of the crystalline phase volume fractions in a trip-assisted duplex stainless steel were performed under loading using electron backscatter diffraction (EBSD), in situ neutron diffraction, and energy selective neutron imaging (ESNI) methods. In contrast to the localized investigations of EBSD, ESNI provides macroscopic spatial distributions in a volume-averaged manner over the entire specimen with a spatial resolution of about 65 μm. The ESNI shows that the martensite is concentrated on the necking region and estimates its volume fraction of 14% at a strain of 0.2, which is comparable to the neutron diffraction result.

Orthodontic archwire composition and phase analyses by neutron spectroscopy

Quantitative metallurgical and phase analyses employing neutron diffraction technique were conducted on two as-received commercial rectangular austenitic stainless steel orthodontic archwires, G&H and Azdent, 0.43×0.64 mm (0.017×0.025 inch). Results showed a bi-phase structure containing martensitic phase (45.67% for G&H and 6.62% for Azdent) in addition to the expected metastable austenite. The former may be a strain-induced phase-transformation arising during the cold working process of wire fabrication. Further neutron resonance capture analysis determinations provided atomic and isotopic compositions, including alloying elements in each sample, complementary to the results of traditional energy dispersive X-ray spectroscopy. Together, these results assist in relating commercial alloying recipes and processing histories with mechanical performance, strength and ductility in particular.

Path length dependent neutron diffraction peak shifts observed during residual strain measurements in U–8 wt% Mo castings

This study reports an angular diffraction peak shift that scales linearly with the neutron beam path length traveled through a diffracting sample. This shift was observed in the context of mapping the residual stress state of a large U–8 wt% Mo casting, as well as during complementary measurements on a smaller casting of the same material. If uncorrected, this peak shift implies a non-physical level of residual stress. A hypothesis for the origin of this shift is presented, based upon non-ideal focusing of the neutron monochromator in combination with changes to the wavelength distribution reaching the detector due to factors such as attenuation. The magnitude of the shift is observed to vary linearly with the width of the diffraction peak reaching the detector. Consideration of this shift will be important for strain measurements requiring long path lengths through samples with significant attenuation. This effect can probably be reduced by selecting smaller voxel slit widths.

Influence of multiple small-angle neutron scattering on diffraction peak broadening in ferritic steel

Peak broadening of neutron diffraction was studied at various neutron wavelengths (1.24–2.61 Å). As the neutron beam path through a specimen increased, significant peak broadening was observed in ferritic steel, but not in austenitic steel. The peak broadening was reduced under a magnetic field applied perpendicular to the beam direction. Small-angle neutron scattering results showed significant reduction in scattering intensities under a magnetic field of 1.2 T. It is suggested that the peak broadening can be attributed to multiple small-angle neutron scattering by magnetic domains. Thus, a sufficiently strong magnetic field could enhance the deep penetration capability of neutron diffraction by reducing the peak broadening.