Naval Surface Warfare Center

About: Naval Surface Warfare Center is a facility organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Radar & Sonar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

Nanoscale Analyses of High-Nickel Concentration Martensitic High-Strength Steels

Abstract: Austenite reversion in martensitic steels is known to improve fracture toughness. This research focuses on characterizing mechanical properties and the microstructure of low-carbon, high-nickel steels containing 4.5 and 10 wt pct Ni after a QLT-type austenite reversion heat treatment: first, martensite is formed by quenching (Q) from a temperature in the single-phase austenite field, then austenite is precipitated by annealing in the upper part of the intercritical region in a lamellarization step (L), followed by a tempering (T) step at lower temperatures. For the 10 wt pct Ni steel, the tensile strength after the QLT heat treatment is 910 MPa (132 ksi) at 293 K (20 °C), and the Charpy V-notch impact toughness is 144 J (106 ft-lb) at 188.8 K (−84.4 °C, −120 °F). For the 4.5 wt pct Ni steel, the tensile strength is 731 MPa (106 ksi) at 293 K (20 °C) and the impact toughness is 209 J (154 ft-lb) at 188.8 K (−84.4 °C, −120 °F). Light optical microscopy, scanning electron and transmission electron microscopies, synchrotron X-ray diffraction, and local-electrode atom-probe tomography (APT) are utilized to determine the morphologies, volume fractions, and local chemical compositions of the precipitated phases with sub-nanometer spatial resolution. The austenite lamellae are up to 200 nm in thickness, and up to several micrometers in length. In addition to the expected partitioning of Ni to austenite, APT reveals a substantial segregation of Ni at the austenite/martensite interface with concentration maxima of 10 and 23 wt pct Ni for the austenite lamellae in the 4.5 and 10 wt pct Ni steels, respectively. Copper-rich and M2C-type metal carbide precipitates were detected both at the austenite/martensite interface and within the bulk of the austenite lamellae. Thermodynamic phase stability, equilibrium compositions, and volume fractions are discussed in the context of Thermo-Calc calculations.

Electronic and atomic structure of Mn-doped CaF2: An x-ray-absorption near-edge structure and extended x-ray-absorption fine-structure study.

Abstract: X-ray-absorption near-edge structure (XANES) and extended-x-ray-absorption fine-structure (EXAFS) measurements have been performed on the calcium K edge and manganese K edge of ${\mathrm{CaF}}_{2}$ doped with manganese at molecular concentrations of 0.1--2.5 %. The results are compared to other measurements of the calcium K edge in ${\mathrm{CaF}}_{2}$ and the Mn K edge in various manganese compounds. Major features in the XANES spectra are tentatively identified with transitions to high-symmetry points of the ${\mathrm{CaF}}_{2}$ energy bands in a one-electron picture. Expected deviations from the structure predicted by the one-electron formalism are discussed. The EXAFS analysis shows a reduction in the manganese-fluorine distance of (3.9\ifmmode\pm\else\textpm\fi{}0.4)% as compared to the calcium-fluorine separation in the doped or undoped samples. This compares well with previous results obtained by EPR. A significant increase in disorder of the first shell around the Mn dopant ion is observed as compared to the Ca ion. The significance of this shell contraction and disorder is discussed in terms of possible defect structures in the material.

Degassing Behavior of Nanostructured Al and Its Composites

Abstract: The synthesis of bulk ultrafine-grained (UFG) and nanostructured Al via cryomilling can frequently require a degassing step prior to consolidation, partly due to the large surface area of the as-milled powders. The objective of this study is to investigate the effects associated with cryomilling with stearic acid additions (as a process-control agent) on the degassing behavior of Al powders. This objective was accomplished by completing select experiments with Al-7.5Mg, Al-6.4 wt pct Al85Ni10La5, and Al-14.3 wt pct B4C. The interaction between Al and stearic acid was determined using thermal analysis combined with Fourier transform infrared spectroscopy (FTIR). The degassing experiments were carried out under high vacuum (10−4 to ~10−6 torr) in a range from room temperature to 400 °C, with the pressure of the released gases monitored using a digital vacuum gage. The results showed that the liberation of chemisorbed water was suppressed in cryomilled Al powders and both the chemisorbed water and stearic acid were primarily released in the form of hydrogen. It was also demonstrated that under certain conditions, a nanostructure (grain size ~100 nm) can be retained following the hot vacuum degassing of cryomilled Al.

Adaptive wavelet classification of acoustic backscatter and imagery

Abstract: The utility and robustness of wavelet features is demonstrated through three practical case studies of detecting objects in multispectral electro-optical imagery, sidescan sonar imagery, and acoustic backscatter. Attention is given to choosing proper waveforms for particular applications. Using artificial neural networks (ANNs), evidence is fused from multiple-waveform types that detect local features. The wavelet waveforms and their dilation and shift parameters are adaptively computed with ANNs to maximize classification accuracy. Emphasis is placed on the acoustic backscatter case study, involving detecting a metallic man-made object from natural and synthetic specular clutter with reverberation noise. The synthetic clutter is shown to be a good model for the natural clutter, which appears promising for avoiding huge data collection efforts for natural clutter and for better delineating the classification boundary. The classifier computes the locations, sizes, and weights of Gaussian patches in time-scale space that contain the most discriminatory information. This new approach is shown to give higher classification rates than an ANN with commonly used power spectral features. The new approach also reduces the number of free parameters in the classifier based on all wavelet features, which leads to simpler implementation for applications and to potentially better generalization to test data.

Structure of melt-spun Fe-Ga based magnetostrictive alloys

Abstract: Fe/sub 1-x/Ga/sub x/ (x=0.17, 0.21, 0.25 and 0.3) alloys were rapidly quenched by the melt-spinning technique to determine the maximum Ga concentration that retains the disordered bcc (/spl alpha/-Fe) phase at room temperature. The texture of the ribbons as a function of melt-spinning parameters and annealing was also extensively studied. All of the as-spun samples were found to be crystalline. For x=0.17, only the disordered bcc phase was found and for x=0.25 and 0.3, primarily DO/sub 3/ phase was found, while for x=0.21, the phase is bcc at high wheel speed and DO/sub 3/ at low speed. For the free side of the as-spun ribbons, the easy growth axis of /spl alpha/-Fe or of DO/sub 3/ tilts about 10/spl deg/ to 20/spl deg/ from the ribbon normal and is along the ribbon length. This texture does not change significantly with wheel speed. The texture on the wheel side of the ribbon is close to random at high speed but increases with slower speed. For Fe/sub 83/Ga/sub 17/, 900/spl deg/C annealing reduces the tilt angle while 1100/spl deg/C annealing recrystallizes the grains and produces strong out of plane texture but randomizes the directionality in the plane. Annealing with sulfur addition was found to enhance the {100} texture but did not produce the desired along the longitudinal direction of the ribbon. The saturation magnetostriction, /spl lambda//sub s/, of as-spun Fe/sub 79/Ga/sub 21/ and Fe/sub 83/Ga/sub 17/ both having a disordered bcc structure and strong {100} texture was measured as 98 and 130 ppm, respectively, along the ribbon length.