Polycapillary optics based neutron focusing for small sample neutron crystallography.

This work presents preliminary measurements designed to explore a new approach to neutron diffraction that is somewhat analogous to the pseudo-Laue technique, except that instead of using a broad energy (wavelength) bandwidth it uses a broad angular bandwidth. We have used a polycapillary focusing optic to focus neutrons from a monochromatic beam (using the BT-8 spectrometer on the NIST research reactor) and from a polychromatic beam at a pulsed spallation source (the Intense Pulsed Neutron Source, IPNS at Argonne National Laboratory) into a small, intense spot and have carried out preliminary diffraction measurements. Using the single crystal diffraction (SCD) facility on IPNS, diffraction of a 3{sup o} convergent beam from an alpha quartz crystal showed six diffraction beams in the 1-5{angstrom} wavelength bandwidth transmitted by the optic. The diffraction spots showed an intensity gain of 5.8 {+-} 0.9 compared to a direct beam diffracting from the same sample volume as that illuminated by the convergent beam

Through-thickness residual stress measurement by neutron diffraction in Cu+W plasma spray coatings.

A range of different spraying techniques can be used to coat the surfaces of engineering components. These techniques are based on different principles and can involve high temperature (plasma spray), high kinetic energy (cold spray) or both (HVOF spray – High-Velocity Oxi-Fuel). Resultant residual stress in such coatings, being a characteristic of the spraying process, can reveal details of the stress formation mechanism. When its dependence on the physical parameters and conditions of the spraying process is established, this knowledge can be used for the prediction and control of stress that occurs in applications. Neutron diffraction is a suitable method for obtaining stress distribution in such coatings. Residual stresses in two-phase Cu+W coatings made by water stabilized plasma spraying were studied. Two-phase coatings develop both significant microstress (inter-phase stress) and the stress dependence on phase content of the coating constituents. Through-thickness residual stress profiles have been measured by neutron diffraction with spatial resolution of 0.5 mm for a series of Cu+W coatings with varying volume fractions. Measurements were made in both phases in order to separate micro- and macro-stresses. Comprehensive sample characterization, measurements of the residual stresses, mechanical and thermal properties of the composite coatings enabled quantitative modeling and interpretation of the experimental data

Use of neutron diffraction for stress measurements in thin and thick thermal sprayed coatings.

Thermal spraying is a widely used and cost effective technique for the surface protection of engineering components. The spectrum of applications is vast: corrosion protection, wear resistance and abrasion resistance, thermal barriers, electrical (dielectric) coatings, etc. Process induced residual stress has long been recognised as an important factor influencing the integrity and overall performance of coatings. Residual stress generation during thermal spraying is a complex phenomenon. Significant efforts have been made to improve understanding of the evolution of residual stresses during deposition and to develop practical models for numerical prediction of stress distributions in coatings. Owing to the high penetrating power of neutrons and spatial resolution in the millimetre and submillimetre range, neutron diffraction is, perhaps, the most versatile method for stress determination, and has been used extensively for experimental validation of theoretical predictions. Examples of neutron diffraction residual stress results are presented to illustrate the capabilities of the technique: a thin (∼0·3 mm) Mo/Mo2C composite HVOF coating, several examples of millimetre thick ceramic and metallic coatings, and thick coatings (∼10 mm) of iron made by spray forming. © 2010, Maney Publishin

Neutron residual stress measurements in rails

Rails were among the first objects of study by neutron diffraction strain measurement and the first experiments were done as early as the late 1980s [1, 2]. This interest is easy to explain: the problem of rail fracturing is critical from the public safety point of view and the penetrating ability of neutrons suggested the possibility of breakthrough experiments and fast progress in this field. It was well-established that residual stresses, both near-surface and interior, played a signifi cant role in the development of defects which led to rail failure. This suggested three distinct approaches of neutron diffraction strain measurement that could contribute to various problems of the rail industry. The first method was to map the complete triaxial stress distribution non-destructively in the interior of an intact rail, ideally before and after significant service. Another approach was to use slices, for example to characterize how different processing methods produce favourable or detrimental stress distributions in rails. A third technique was to make non-destructive measurements, but in critical and not very deep portions of rails, for example, to examine defects and their relation to rail failure in the top running surface of rails, e.g. white layer formation

Stress profiling in cold-spray coatings by different experimental techniques: neutron diffraction, x-ray diffraction and slitting method

The residual stress profiles in Cu and Al coatings sprayed using kinetic metallization to thickness of 2 mm have been studied. Due to specific parameters of the cold-spray process and particular combination of materials, coatings and substrates, the residual stresses are low with magnitudes of the order of a few tens of MPa. This poses challenges on accuracy and resolution when measuring through-thickness stress distributions. Three experimental techniques - neutron diffraction, X-ray diffraction and a slitting method- were used to measure through thickness stress distributions in the substrate-coating systems. All three techniques demonstrated acceptable accuracy and resolutions suitable for analyzing stress profiles. Advantages and disadvantages of each technique are discussed

Evaluation of biaxial flow stress based on elasto-viscoplastic self-consistent analysis of X-ray diffraction measurements

Biaxial flow behavior of an interstitial free steel sample was investigated with two experimental methods: (1) Marciniak punch test with in situ X-ray diffraction for stress analysis; (2) hydraulic bulge test. The stress analysis based on X-ray diffraction using (211) lattice planes was accompanied by the use of stress factors and intergranular (IG) strains. Stress factors and IG strains were experimentally obtained ex situ on samples after prescribed equi-biaxial deformations. An elasto-viscoplastic self-consistent (EVPSC) crystal plasticity model was used to predict the stress factors and the IG strains. The model predictions of the stress factors were in good agreement with the experiments. However, the predictions of IG strains were in poor agreement with their experimental counterparts. As a result, the flow stress solely based on the computationally predicted stress factors and IG strains was unrealistic. The input of the experimental stress factors and IG strains for stress analysis improved the agreement with a reference flow curve obtained by a hydraulic bulge tester. The resulting flow curves based on X-ray diffraction were in good agreement with that of the bulge test up to an effective strain of 0.3. However, an unrealistic softening was observed in larger deformations regardless of whether the stress factor used were experimentally measured or determined from EVPSC calculations. (C) 2014 Elsevier Ltd. All rights reserved.X11169Nsciescopu