were performed on cross sections of compact tension specimens that were used for SCC crack growth rate testing in simulated PWR primary water. Hardness and the EBSD integrated misorientation density could both be related to the degree of cold work for materials of similar grain size. However, a microstructural dependence was observed for strain correlations using EBSD and hardness which should be considered if this technique is to be used for gaining insight on SCC growth rates

While thermal expansion data exists for quenched (as well as aged) U-6wt%Nb, there is wide variation in the reported room temperature elastic moduli. To better understand the room temperature elastic behavior and to address the complete absence of data on the temperature dependence of the elastic moduli, room temperature and in-situ elevated temperature resonant ultrasonic spectroscopy (RUS) was performed along with x-ray diffraction (XRD) and dilatometry using a thermomechanical analyzer (TMA). An in-situ small-and wide-angle x-ray scattering (SAXS/WAXS) experiment was performed on a com-panion sample to help interpret the results. The room temperature polycrystalline dynamic moduli were measured to be E = 95.4 +/- 4.5 GPa and G = 35.2 +/- 0.2 GPa, respectively. As the temperature is raised, the stiffness slowly decreases, consistent with the empirical rule proposed by Varshni, up to the point of precipitation of the equilibrium alpha-U phase, which is stiffer than the martensitic phases. Homogeniza-tion theory of composites can be used to rationalize the observed response at high temperatures and after high-temperature exposures. Aging of the material at low temperatures ( <= 200 degrees C) does not affect the linear elastic stiffness, but does impact the damping behavior which can be measured through RUS. This change in damping provides another perspective on the microstructure changes induced by low -temperature aging which also result in significant strengthening.(c) 2023 Elsevier B.V. All rights reserved.

The effect of microstructure on the internal hydriding behavior of both cast (1 mm grain size) and rolled (25 mu m grain size) uranium containing hydrogen concentrations between 0 and 1.8 wppm were evaluated via small angle neutron scattering (SANS). Increasing hydrogen content up to 1.8 wppm in the cast uranium only weakly affected the average uranium hydride (UH3) precipitate size, calculated from the SANS data. Conversely, the UH3 phase fraction was found to strongly depend on the hydrogen content in the same cast samples. A substantially reduced UH3 particle size distribution was observed in the rolled uranium relative to cast uranium containing the same nominal hydrogen content. It is hypothesized that the suppression of UH3 formation in the rolled uranium is driven by increased hydrogen trapping at grain boundaries, and theoretical calculations that account for trap density, potency, and hydrogen diffusion kinetics support this hypothesis.

The elevated temperature phase transformation kinetics of U-6wt pct Nb in both wrought and cast conditions were investigated using in-situ high-energy synchrotron X-ray scattering. The evolution of the phase content, γ-phase composition, and microstructure morphology was determined through the analysis of simultaneously collected wide-angle diffraction and small-angle scattering (SAXS) data. The results of the wide-angle scattering analysis, especially the phase fractions and average composition of the γ-phase, provide model parameters to enable a quantitative analysis using the SAXS data. Greater clarity regarding the kinetics of different precipitation mechanisms, namely the continuous precipitation (CP) of α-U within the γ-phase matrix and the discontinuous (DP) grain boundary precipitation of a lamellar microstructure, consisting of α-U and Nb-rich γ-phase is obtained from the coupled measurement modes. These results indicate that the CP mechanism is responsible for the initial precipitation of α-U at all temperatures considered. Near the nose in the time–temperature-transformation (TTT) diagram at ~ 798 K, both mechanisms are active during the early stages of phase transformation. However, the DP mechanism has an increasingly long incubation period with decreasing temperature below the TTT nose. The average interlamellar spacing obtained from the SAXS analysis increases with time, providing further evidence of the so-called divergent DP behavior previously observed in U-6wt pct Nb alloys.

the Division of Technical Support (SGTS) convened the 'Experts and Users Advisory Meeting on Laser Induced Breakdown Spectroscopy (LIBS) for Safeguards Applications' also held at IAEA headquarters (July 2008). This meeting was attended by 12 LlBS experts from the Czech Republic, the European Commission, France, the Republic of South Korea, the United States of America, Germany, the United Kingdom of Great Britain, Canada, and Northern Ireland. Following a presentation of the needs of the IAEA inspectors, the LIBS experts agreed that needs as presented could be partially or fully fulfilled using LIBS instrumentation. Inspectors needs were grouped into the following broad categories: (1) Improvements to in-field measurements/environmental sampling; (2) Monitoring status of activities in Hot Cells; (3) Verify status of activity at a declared facility via process monitoring; and (4) Need for pre-screening of environmental samples before analysis. The primary tool employed by the IAEA to detect undeclared processes and activities at special nuclear material facilities and sites is environmental sampling. One of the objectives of the Next Generation Safeguards Initiative (NGSI) Program Plan calls for the development of advanced tools and methodologies to detect and analyze undeclared processing or production of special nuclear material. Los Alamos National Laboratory is currently investigating potential uses of LIBS for safeguards applications, including (1) a user-friendly man-portable LIBS system to characterize samples in real to near-real time (typical analysis time are on the order of minutes) across a wide range of elements in the periodic table from hydrogen up to heavy elements like plutonium and uranium, (2) a LIBS system that can be deployed in harsh environments such as hot cells and glove boxes providing relative compositional analysis of process streams for example ratios like Cm/Up and Cm/U, (3) an inspector field deployable system that can be used to analyze the elemental composition of microscopic quantities of samples containing plutonium and uranium, and (4) a high resolution LIBS system that can be used to determine the isotopic composition of samples containing for example uranium, plutonium... etc. In this paper, we will describe our current development and performance testing results for LIBS instrumentation both in a fixed lab and measurements in field deployable configurations.

In-situ high energy x-ray scattering experiments enable high temporal resolution investigations of precipitation kinetics; Continuous and discontinuous precipitation are competitive near the TTT nose (~525°C); The incubation time for discontinuous precipitation increases significantly at temperatures below the TTT nose; Additional evidence for the divergent interlamellar spacing was observed at 434°C and 466°C

Tensile plastic deformation and fracture behavior of a laser powder bed fusion processed 316L stainless steel alloy was investigated in situ using high-resolution synchrotron x-ray computed microtomography (sXCT). Three different cases were studied: (1) specimen A1, near full-density with initial porosity of 0.04%, (2) specimen B1, initial lack-of-fusion (LOF) porosity of about 3% with the major axis of defects aligned nearly perpendicular to the tensile loading direction (LD), and (3) specimen B, similar to B1 but with the major axis of LOF defects aligned nearly parallel to LD. The effects of type, density, and orientation of defects in as-printed samples on plastic deformation and failure modes were studied by analyzing sXCT image sequences and quantitative defect properties. Specifically, the evolutions of porosity, size, aspect ratio, and angle of gas pores and LOF defects were characterized as a function of applied strain. Moreover, interactions between as-printed defects and deformation-induced crack propagation were investigated. The tensile behavior of specimen A1 was comparable to that of a commercial wrought plate. The quantitative in-situ sXCT results showed a void-growth phenomenon in A1 but without noticeable coalescence, resulting in a ductile cup-cone failure. Specimen B1 showed damage-driven brittle failure with limited plasticity due to early and rapid propagation of open voids. On the other hand, specimen B, with a similar amount of LOF defects as B1, showed deceivingly strong and ductile tensile behavior similar to A1 without any major crack propagations due to the favorable orientation relationship between LOF defects and the LD.

The micromechanics of plastic deformation behavior of a selective laser melt processed austenitic stainless steel were studied by investigating the evolutions of texture and intergranular strain using in situ high-energy synchrotron x-ray diffraction (sXRD). The effects of defect characteristics on tensile behavior were studied using three different samples: a near full-density sample with elliptical closed voids and two samples with lack-of-fusion (LOF) defects tensile loaded either perpendicular or parallel to their major axes. The evolutions of pole figures and inverse pole figures show that the full-density specimen develops a strong (111)/(200) fiber texture along the loading direction. For both LOF specimens, the evolution of texture is qualitatively similar to the full-density counterpart, but the development of the fiber texture was much slower, indicating a limited plasticity at a given macroscopic strain. The intergranular strain evolution in the full-density specimen is similar to that of a wrought 316L stainless steel. Conversely, a significantly different intergranular strain development was observed in a LOF specimen, where tensile strain development was observed in both the axial and transverse directions. The influence of defect type, density, and orientation on the local stress states in the steel matrix and the evolutions of intergranular strains is discussed.

Elastic mechanical properties of 316 L stainless steel samples fabricated using laser powder bed fusion were studied non-destructively through resonant ultrasound spectroscopy. Samples in five different conditions were obtained by varying the laser power from 103 W (the highest density condition) to 68 W (the lowest density condition) at constant laser speed, producing samples with a volume energy density in the 24.5-16.5 J/mm(3) range and volumetric porosity in the 0.1-10% range. The observed elastic mechanical properties are discussed taking into consideration the bulk texture developed and quantitative pore characteristics studied using high-energy high-resolution synchrotron X-ray diffraction and X-ray computed micro-tomography, respectively. Furthermore, empirical exponential relationships are provided to express the functional dependence of Young's and shear moduli with porosity.

The effect of laser power on defect characteristics, microstructure development, constituent phases, and crystallographic texture was studied on a laser powder bed fusion (L-PBF) processed 316L stainless steel. A series of specimens was additively manufactured as a function of laser power ranging from 380 to 200 W with a fixed scan speed of 300 mm/s. The density, size, shape, and orientation of pores in as-printed L-PBF cylinders were characterized using high-resolution synchrotron X-ray computed microtomography with a 0.65 mu m resolution. The changes in the texture and phases were investigated using high-energy synchrotron X-ray diffraction. The melt pool shape and grain size/orientation were also analyzed using metallography. The results show that the porosity increases linearly from 0.13 to 0.88% with the decrease in laser power. However, even with a decrease in laser power by about half and corresponding seven-fold increase in porosity, the 200W case can still be considered as nearly fully dense. On the other hand, with the same decrease in the laser power, the cellular spacing was refined from 1.5 to 0.75 mu m and the texture changed from strong (200) to random. Therefore, within an optimal porosity range, it is feasible to manipulate microstructure significantly using the control of laser power. (C) 2018 The Authors. Published by Elsevier Ltd.

Resonant ultrasound spectroscopy (RUS) was used to study the elastic mechanical properties and internal friction of two wrought magnesium alloys, AZ31B and ZK60A, from 25 degrees C to 450 degrees C. Samples in the rolled, transverse, and normal directions were characterized at 50 degrees C intervals to determine the temperature dependency of elastic moduli and stiffnesses for each direction. The temperature dependencies represented as, dE/dT, dG/dT, dB/dT, dC(11)/dT, dC(12) /dT, and dC(44)/dT are provided herein, To evaluate the RUS technique for these type of alloys, Young's modulus was also determined by conventional static tension testing and the results were compared. From the same RUS experiment, the internal friction variation with temperature was calculated for both alloys. The linear coefficients of thermal expansion for each direction over the temperature range considered were determined, as they were needed to estimate sample dimension at elevated temperature for the RUS measurements. This study shows that RUS can be a convenient and accurate technique to supply quantitative elastic mechanical data and fill the existing gaps on light metals characterization.

Using a compact hand-held laser-induced breakdown spectroscopy (LIBS) instrument, studies were conducted on specimens of uranium charged with controlled hydrogen concentrations for a qualitative evaluation of hydride corrosion. Four samples of depleted uranium with two different starting microstructures (cast and rolled) were used for this study. The hydrogen charged samples (rolled 1.8 wppm H and cast 14 wppm H by weight) are representative of the pre-corrosion states with hydrides distributed throughout the bulk. In-depth LIBS measurements were carried out, after the thick surface corrosion layer was removed, by applying 100 laser pulses from sample surface into the bulk on five different sample locations. Three additional areas on each sample were studied by laser ablation using a 12-point grid approach. The atomic emission signals of elemental uranium, carbon, hydrogen, and oxygen were identified and analyzed. All four samples showed similar uranium and carbon concentrations, as expected. Hydrogen content was consistent with each sample's specification, such that the hydrogen charged samples exhibited higher hydrogen concentration than their references. Both specimens charged with hydrogen showed elevated oxygen content as well, due to rapid oxidation of uranium and uranium hydrides. The oxidation process was facilitated by the laser ablation and plasma plume's high temperature effects on the sample combined with the glovebox environment. The uranium surface damage produced by laser ablation was quantitatively evaluated by optical microscopy.

In-situ strain neutron diffraction measurements were conducted at temperature on specimens coming from a clock-rolled alpha-uranium plate, and Elasto-Plastic Self-Consistent (EPSC) modeling was employed to interpret the findings. The modeling revealed that the active slip systems exhibit a thermally activated response, while deformation twinning remains athermal over the temperature ranges explored (25-150 degrees C). The modeling also allowed assessment of the effects of thermal residual stresses on the mechanical response during compression. These results are consistent with those from a prior study of room-temperature deformation, indicating that the thermal residual stresses strongly influence the internal strain evolution of grain families, as monitored with neutron diffraction, even though accounting for these residual stresses has little effect on the macroscopic flow curve, except in the elasto-plastic transition. (C) 2018 Elsevier B.V. All rights reserved.

rapidly solidified alloys and AM. HEXRD can probe small volumes at fast rates and provides a wide range of thermomechanical and kinetic information. This thesis presents the application of HEXRD to rapidly solidified titanium and stainless steel alloys through a series of case studies. In the first two studies, HEXRD is applied to rapidly solidified titanium and stainless steel welds. The materials are characterized for their temperature history, phase changes, kinetics, and microstructural evolution. In the next case study, HEXRD is applied to characterize phase changes in elastocaloric NiTi shape memory alloys (SMAs) under thermomechanical load. HEXRD, in conjunction with other tools, is used to explain the superior performance of the additively manufactured SMAs. In the final two case studies, HEXRD is used to measure the mechanical response of AM parts with complex geometries; namely, the octet truss lattice. Diffraction reveals a wide range of materials information about the AM microstructure including unexpected phases, texture, and mechanical response to loading. The mechanical results from HEXRD and then compared with theoretical predictions about the performance of octet truss lattices. Summarily, HEXRD is a diverse tool that is poised to address the complex characterization problems of many aspects of the additive manufacturing process.