To improve the reliable integration of additively manufactured (AM) metal components, there is an urgent need for surface finishing methods capable of processing rough, “as-printed” surfaces. We present a new and scalable electropolishing (EP) technique for use on AM 316L stainless steel (SS) that is capable of achieving a surface roughness equivalent to a machined finish, with arithmetic mean heights ( S a ) as low as 1.0 µ m. This technique utilizes the sequential application of a new, NaCl/H 2 O pulse/pulse reverse (P/PR) EP step along with a conventional DC (direct current) EP step, where P/PR expands the capability of EP by removing roughness features > 1 µ m, which has been previously unattainable with DC EP alone without substantial material removal. This is achieved by independently varying pulse parameters, such as pulse width and height, allowing more control over electrodynamic processes at the part-electrolyte interface. Additionally, P/PR EP resulted in higher smoothing efficiency, where a higher degree of smoothing was achieved with less material removal when compared with conventional DC EP alone. This minimizes unwanted change in geometry from excessive metal dissolution.

on inert atmospheres. Preparations for studies of phases produced in the region between rare earth metals and their nitrides are reported. Data are also included on the infrared spectra of rare earth hydroxides, and onides which provide information on the type and intensity of the hydroxide bonding. A study of kinetics in high vacuum reduction or decomposition of mixed rare earth oxides is also being made. Preliminary investigations are being conducted to select the mixing agent from among ytterbium, erbium, and lutetium oxides. Papers for publication on the oxidation kinetics of cerium and lanthanum are included. (J.R.D.)

of the possibility of compliance with standards which would conform to the US Envionmental Protection Agency's (EPA) Interpretative Ruling of December, 1976. Only under a fortuitous set of regulations and events is it likely that compliance will be demonstrated. If the San Francisco Bay Area or if the vicinity of a proposed site is deemed not a non-attainment area for particulates, or if it is and trade-offs can be obtained through very diligent efforts; if ambient CO standards are being met through futher reduction of automotive pollution; and finally if NO/sub x/ offsets can be obtained through retrofitting existing PG and E facilities - a difficult task according to all parties; if all of these conditions prevail, then PG and E might demonstrate compliance. The Committee notes that it is the Staff's opinion that some of these tasks will be extremely difficult if not impossible to accomplish. The Committee recommends that the Commission approve the NOI and allow PG and E to make the decision whether or not to pursue an AFC. But for its own planning purposes, the Commission would be unwise to count on this poject.

Thermal aging models and lifetime predictions for uranium-niobium (U-Nb) alloys were created using an approach similar to those previously employed. Lifetime estimates for generic U-6Nb components were thus updated; the reported value being 800 years. This update represents a small change in lifetime vs. that of the 2012 assessment (540 years). This lifetime estimate emerged from consideration of several model fits specific to the aging datasets and properties chosen. Aging was quantified using quasi-static tensile properties measured on specimens artificially aged for up to 10 years. The major change relative to the most recent 2012 LANL assessment was that a more comprehensive body of U-Nb literature data was mined, in addition to being augmented by the latest LANL and UK AWE data. The tensile data compilation was published separately (LANL report LA-14493, December 2016). Recognizing the chemical banding of industrially produced U-6Nb, models were developed for the mid-range (6 wt.%) and extrema (4 and 8 wt.%) compositions. Lifetime estimates were calculated for all three alloy classes (4, 6, 8 wt.% nominal) and two measures of total tensile elongation (TE) to failure, namely TE-ext. — extensometer method, and TE-NCD — normalized crosshead displacement method. The conservative assumption was made that whichever composition (4, 6, or 8 wt.% Nb) and property (TE-ext or TE-NCD) was the first to cross the ductility failure threshold would limit the lifetime of the entire component. Tensile strength properties did not figure into the lifetime predictions, but could be useful as age-sensitive diagnostics and were also modeled. Of these, only first yield strength is expected to show a change at 40°C aging vs. time = 0 over the ~100-year timespan of engineering interest. Second yield strength evolves more slowly, and ultimate tensile strength slower still. Among all the models, the apparent activation energies for aging were mostly in the narrow 29– 37 kcal/mol range, which is close to that for diffusion of Nb in gamma-uranium. This agreement may be coincidental. The data from recent long-term aging studies substantially improved the model fit quality and robustness of the lifetimes. Appendices document sensitivity studies of the model fits and lifetimes with respect to using more limited datasets. These results highlight the limitations of relying solely on data from scattered literature studies and smaller datasets more generally.

In-situ time-of-flight neutron diffraction experiments were performed on uranium-niobium alloy with 6 wt% Nb to study the lattice parameter-composition relationship for the body centered cubic (bcc) alloys. Based on lattice-parameter measurements of Nb-supersaturated gamma s phase over the range of 450 - 790 degrees C, an improved Vegard's-type relationship was established for determination of Nb concentrations at elevated temperatures. Neutron diffraction data were also collected as a function of aging time over the 450 - 600 degrees C range when gamma s phase decomposed isothermally into the mixture of orthorhombic alpha-U and Nb-rich bcc phase, as well as at room-temperature on the alloys aged ex-situ at 500 degrees C up to five years. From these measurements, the average Nb concentrations in the bcc phase were determined based on the Rietveld refinements of weight fraction and mass conservation relations (lever rule). Over the 15at% - 78 at% range of Nb concentrationsthatcorrespond to different experimental aging times, the lattice parameters at constant temperatures exhibit a nonlinear S-shaped variation with Nb concentration, and the associated excess volumes of mixing can be described by a subregular solution model of the Redlich-Kister type of polynomial. Over the full range of composition the S-shaped deviation from Vegard's law can be modeled using a combination of an elastic continuum model and a perturbation to the radii of the solute atoms in the solvent, suggesting that electronic interactions between solute and solvent atoms could play an important role in the compositional dependence of lattice parameter for the gamma-phase U-Nb alloys. While Vegard's law is a straightforward and reasonably good approximation for the bcc solid solutions in the U-Nb system, the Nb concentrations determined from the weight fraction refinements of diffraction data provide internally consistent, mass-conserving estimates of solute redistribution for the monotectoid reaction. Published by Elsevier B.V.

U-Nb’s discontinuous precipitation, γmatrixbcc→αcellularorth+γcellular′bcc, is intriguing in the sense that it allows formation and growth of the metastable γ′ phase during the course of its occurrence. Previous attempts to explain the thermodynamic origin of U-Nb’s discontinuous precipitation hypothesized that the energy of α forms an intermediate common tangent with the first potential of the double-well energy of γ at the γ′ composition. In this work, we examine different possible mechanisms by which the discontinuous precipitation product in the U-Nb system can be stabilized. We put forward a mechanism by which the bulk free energy of the γ can develop a non-monotonic dependency with composition. Additionally we posit that local contributions due to lattice mismatch between the α and γ phases may be responsible for the generation of metastable states that may stabilized by thermodyna mics as well as by kinetics. Our work suggests that local misfit strain tends to play a crucial role in the growth of the discontinuous precipitation product. Depending on the magnitude of strain developed at the α/γ′ interfaces, either an increasing γ′ composition or a random distribution of γ′ compositions around the equiatomic value with respect to increasing temperature could be expected. Moreover, we show how it is possible to stabilize the discontinuous precipitation front through highly anisotropic and fast interface diffusion.

This work explored ways to data mine legacy literature and predict solid-solid precipitation in support of simpler assessment of corrosion propensity in metallic alloys. Of interest was locating the peak age watershed (maximum hardness or strength), beyond which lies the regime termed “overaging.” A diligent search of literature and reference books, discussions with SMEs, and application of various algorithms showed that none of the premises going in held up to scrutiny.

U-Nb's discontinuous precipitation, $\gamma^{bcc}_{matrix} \rightarrow \alpha^{orth}_{cellular} + \gamma'^{bcc}_{cellular}$, is intriguing in the sense that it allows formation and growth of the metastable $\gamma'$ phase during the course of its occurrence. Previous attempts to explain the thermodynamic origin of U-Nb's discontinuous precipitation hypothesized that the energy of $\alpha$ forms an intermediate common tangent with the first potential of the double-well energy of $\gamma$ at the $\gamma'$ composition. While this hypothesis is eligible and consistent with the experimental observation of gradual increase in $\gamma'$ composition at increasing temperature, it is in conflict with recent experiments whose results indicated a distribution of $\gamma'$ compositions in the vicinity of 50 at\%Nb. To shed some light onto this issue, the current work investigates the origin of U-Nb's discontinuous precipitation in view of fundamental thermodynamics and kinetics, taken from the perspective of phase-field theory. It has been showed that local misfit strain tends to play a crucial role in the formation and growth the discontinuous precipitation. Depending on the magnitude of strain developed at grain boundaries, either an increasing $\gamma'$ composition or a random distribution of $\gamma'$ composition around the equiatomic value with respect to increasing temperature could be expected.

In this work, we conducted in-situ high P-T neutron diffraction experiments on U-7.7Nb. Our results show that the tetragonal (o) phase is substantially more compressible than the monoclinic phase. As the pressure increases, this leads to increased volume collapse and stress relaxation for the reverse martensitic transformation, (o). At moderately elevated temperatures, a substantial strain-induced stabilization against transformation into a body centered cubic phase was observed in the (o) phase. We also found that the ability to retain the metastable phase, formed from rapid heating of thermally reset (o), has subtle dependence on the austenitization temperature. The present findings provide a direct test for the hypotheses proposed to explain the low-pressure shock behaviors of the U-Nb alloys.

Two low-carbon 9-Cr ferritic-martensitic steels were designed with the aim of decreasing M23C6 and maintaining or increasing MX phase fraction. A low-carbon (LC) alloy and a low-carbon, zero-niobium (0Nb) alloy were fabricated, their designs based upon the P92 alloy system. Solutionizing temperatures to maximize V and Nb in solution while avoiding delta-ferrite were determined to be 1170 degrees C for the P92 alloy and 1050 degrees C for LC and ONb, significantly lower than predicted using ThermoCal (R) modeling. As was intended, the M23C6 phase fraction was reduced for LC and ONb alloys after both heat treating and aging relative to the base P92 alloy, as determined by wide angle x-ray scattering (WAXS) analysis. Dislocation density measurements from x-ray line broadening in P92 and LC suggest these alloys had more stable dislocation substructures than ONb at lower temperature and shorter time aging conditions. While LC exhibited lower microhardness than P92 at room temperature, the tensile properties were comparable at 650 degrees C, suggesting that elevated temperature strength can be achieved with lower carbon contents. Aging studies showed that P92 had a more stable microstructure for higher temperature and longer time aging conditions. The P92 alloy also had a longer stress rupture life, implying that the M23C6 precipitate contribution to thermal stability is important. Evidence of Z-phase was discovered for the LC alloy aged 10,000 h at 650 degrees C, corresponding to decreased strength and increased ductility. Overall, the stress rupture lives of the modified heat-treatment variations of P92 and LC compare favorably to literature values for 9% Cr steels with conventional heat treatments.

In situ time-resolved synchrotron X-ray diffraction experiments were conducted to study the fine-scale phase evolution of U-6Nb. Upon rapid heating from 125 °C to 400 °C, a reverse martensitic transformation sequence, α″ → γo → γs, was observed in less than 4 seconds, which represents the first direct observation of the γo → γs transformation in diffraction-based measurements. Consistent with previous ex situ metallography experiments, our isothermal hold experiments at 526 °C, 530 °C and 565 °C reveal two distinct reactions for the phase separation, γs → α-U + γ1 (general precipitation) followed by (α-U + γ1) → α-U + γ1-2 (discontinuous precipitation). For the first-stage precipitation, the incubation time is determined to be ~ 50 and 100 seconds, respectively, for the isothermal aging at 526-530 °C and 565 °C. At this stage, the phase transformation is characterized by the simultaneous growth of α-U and γ1 at the expense of γs. As expected from the Arrhenius equation for the reaction rate, the determined times (~ 23 minutes) for the completion of the first-stage reaction at 526 ± 3 °C and 530 ± 3 °C are nearly twice longer than that at 565 ± 4 °C (~ 13 minutes). Over these periods of time, the Nb contents derived from a Vegard’s-type relationship for γ1 are in the 30.2 to 32.1 and 29.2 to 30.6 at. pct ranges, and the kinetics of the precipitation at 565 ± 4 °C can be described by the classic Avrami rate equation and one-dimensional growth of a surface or grain-boundary nucleation. During the second-stage precipitation, the γ1 phase continues to enrich in Nb as it gradually evolves toward the α + γ1-2 metastable state (up to 47 at. pct over a period of 172 minutes at 530 °C). These new and time-resolved measurements can be used to better constrain the time–temperature–transformation diagram, solute (Nb) redistribution, and transformation kinetics during the early stages of the diffusional phase transformation.

On 2 April 2018, a high explosive violent reaction (HEVR) occurred during routine pressing of a 1-in -diameter cylindrical pellet of PBX 9501 high explosive. Fragments of the die set (die body and stemples) involved in the event were sent to Sigma Division for metallurgical analysis. A handheld x-ray fluorescence alloy tester confirmed the die set material to be A2 tool steel. Light optical microscopy revealed what appear to be pre-existing flaws on the inner diameter of the die body. Scanning Electron Microscopy could neither confirm nor exclude the presence of fatigue cracking in the vicinity of these potential flaws. Energy Dispersive Spectroscopy indicated the presence of a carbon-bearing residue on fracture surfaces; nitrogen-bearing residue was also found. Optical microscopy revealed that the microstructure of the stemple and inner diameter of the die body contained large stringers and non-uniform grain size; this was distinct from the relatively clean and uniform microstructure seen at the outer diameter of the die body, and also other A2 tool steel stock (pedigree unknown and with no known connection to any HE pressing hardware) that was examined for additional comparison. Rockwell hardness testing indicated the material was heat treated properly. Metallographic analysis alone could not positively identify the root cause of the event, but, coupled with accounts provided by the operator and the successful history with the particular lot of HE involved in the event, points to ward mechanical failure of the die set due to pre -existing flaw as the most likely precipitating event. Suggestions for additional analyses and future qualification techniques are discussed.

Overall kinetics of lamellar overaging reactions in U-5.5Nb and U-7.5Nb were analyzed by Avrami-Arrhenius analyses of volume fractions measured from an extensive temperature-time (T-t) matrix of specimens. The cellular initiation site (grain boundaries, inclusions) and regimes of lamellar divergency-cum-slowing growth rate were explicitly accounted for. Avrami exponents n from T-t regimes of constant-growth rate were consistent with theory (1< n <3); those from divergent T-t regimes were smaller, n ~0.7, which is not surprising given their different growth rate behavior. The apparent activation energies Q were similar for grain-boundary and inclusion-nucleated discontinuous precipitation, indicating that their nucleation site does not alter their overall kinetics. Avrami Analysis of Isothermal Aging Kinetics

A tool named Cinema: Debye-Scherrer to visualize the results of a series of Rietveld analyses is presented. The multi-axis visualization of the high-dimensional data sets resulting from powder diffraction analyses allows identification of analysis problems, prediction of suitable starting values, identification of gaps in the experimental parameter space and acceleration of scientific insight from the experimental data. The tool is demonstrated with analysis results from 59 U-Nb alloy samples with different compositions, annealing times and annealing temperatures as well as with a high-temperature study of the crystal structure of CsPbBr3. A script to extract parameters from a series of Rietveld analyses employing the widely used GSAS Rietveld software is also described. Both software tools are available for download.

This translation of report CEA-R-5070, from the French original, was done during September-November 2018, using Google Translate, a web-based service, translate.google.com. After the initial translation through Google Translate, the text was corrected to avoid mistranslation where the author's intent was reasonably clear.

In-situ time-of-flight neutron diffraction experiments were conducted on the uranium-niobium alloy with 6 wt. % Nb (U–6Nb) at pressures up to 4.7 GPa and temperatures up to 1073 K. Upon static compression at room temperature, the monoclinic structure of U–6Nb (α″ U–6Nb) remains stable up to the highest experimental pressure. Based on the pressure-volume measurements at room temperature, the least-squares fit using the finite-strain equation of state (EOS) yields an isothermal bulk modulus of B0 = 127 ± 2 GPa for the α″-phase of U–6Nb. The calculated zero-pressure bulk sound speed from this EOS is 2.706 ± 0.022 km/s, which is in good agreement with the linear extrapolation of the previous Hugoniot data above 12 GPa for α″ U–6Nb, indicating that the dynamic response under those shock-loading conditions is consistent with the stabilization of the initial monoclinic phase of U-6Nb. Upon heating at ambient and high pressures, the metastable α″ U–6Nb exhibits complex transformation paths leading to the diffusional phase decomposition, which are sensitive to applied pressure, stress state, and temperature-time path. These findings provide new insight into the behavior of atypical systems such as U-Nb and suggest that the different U-Nb phases are separated by rather small energies and hence highly sensitive to compositional, thermal, and mechanical perturbations.

The mechanical properties of uranium-niobium alloys evolve with aging at relatively low temperatures due to subtle microstructural changes. In-situ neutron diffraction measurements during aging of a monoclinic U-6Nb alloy at temperatures to 573 K were performed to monitor these changes. Further, in-situ neutron diffraction studies during deformation of U-6Nb in the as-quenched state and after aging for two and eight hours at 473 K were completed to assess the influence of microstructural evolution on mechanical properties. With heating, large anisotropic changes in lattice parameter were observed followed by relaxation with time at the aging temperature. The lattice parameters return to nearly their initial values with cooling. The active plastic deformation mechanisms including, in order of occurrence, shape-memory de-twinning, mechanical twinning, and slip-mediated deformation do not change with prior aging. However, the resistance to motion of the as-quenched martensitic twin boundaries increases following aging, resulting in the observed increase in initial yield strength. (C) 2016 Elsevier B.V. All rights reserved.

The goal of this paper is to analyse the effect of adding Al on the non-steady pearlite growth occurring in a Fe–C–Mn system. The results are discussed in terms of the partitioning of elements across the austenite/ferrite and austenite/cementite interfaces, and the modification of the pearlite driving force related to the change in carbon activity in austenite.