In Situ Neutron Diffraction Measurement during Bainite Transformation and Accompanying Carbon Enrichment in Austenite at iMATERIA, J-PARC MLF

The authors have developed the in situ neutron diffraction technique focusing on bainite transformation during austempering. Thanks to the features of time-of-flight type neutron diffraction, textures, phase fractions and lattice parameters can be simultaneously measured at high temperature. In this paper, the design of experimental equipment and analytical approach are mainly described.

THE EFFICACY OF THE INHERENT STRAIN METHOD IN DETERMINING RESIDUAL STRESS IN IN718 SLM SPECIMENS

This paper presents a study showing the efficacy of the inherent strain method and modifications thereof to predict residual stresses within selective laser melted components. Cubic specimens with variations in hatch rotations were produced, and the residual stress state was simulated and measured by employing the neutron diffraction technique. Variances in the simulated and observed values of stress in the samples were investigated to show the efficacy of the isotropic, orthotropic, and thermo-mechanical simulation methods. The simulations indicated a suitable prediction of the residual stress with the incorporation of hatch rotation, but as being less adept at resolving the residual stress of the components with no hatch rotation. The most accurate simulation results in the horizontal stress directions were seen for the 90° hatch rotation specimen, for which the average difference between the measured and simulated values were below 65 MPa for all simulation types. The simulations largely over-predicted Z direction compressive stresses; however, the thermo-mechanical simulation type predicted this stress with an average difference of 116, 98, and 72 MPA for the 0°, 67°, and 90° hatch rotations respectively.

Crystal structure of monoclinic hafnia (HfO2) revisited with synchrotron X-ray, neutron diffraction and first-principles calculations

A study on the crystal structure of monoclinic HfO2 has been performed using synchrotron X-ray and neutron diffraction data separately, as well as a combination of both. The precision of the structural parameters increases significantly due to application of the neutron diffraction technique. The experimental oxygen positions in HfO2, derived precisely, are visualized only by semi-local density functional calculations in terms of the calculated electronic band gap, but are not captured as accurately by using hybrid functionals.

An introduction to neutron reflectometry

Specular neutron reflectivity is a neutron diffraction technique that provides information about the structure of surfaces or thin films. It enables the measurement of the neutron scattering length density profile perpendicular to the plane of a surface or an interface, and thereby gives access to the profile of the chemical composition of the film. The wave-particle duality allows to describe neutrons as waves; at an interface between two media of different refractive indexes, neutrons are partially reflected and refracted by the interface. Interferences can occur between waves reflected at the top and at the bottom of a thin film at an interface, which gives rise to interference fringes in the reflectivity profile directly related to its thickness. The characteristic sizes that can be probed range from 5Å to 2000 Å. Neutron-matter interaction directly occurs between neutron and the atom nuclei, which enable to tune the contrast by isotopic substitution. This makes it particularly interesting in the fields of soft matter and biophysics. This course is composed of two parts describing respectively its principle and the experimental aspects of the method (instruments, samples). Examples of applications of neutron reflectometry in the biological domain are presented by Y. Gerelli in the book section “Applications of neutron reflectometry in biology”.