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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Characterization of the microstructure of Nb-1wt.%Zr-0.1wt.%C tubes as affected by thermomechanical processing

Microstructure of Nb-1Zr-0.1C tubes were characterized as affected by extrusion temperature of the tube shell and its thermomechanical processing to tubing. Two tube shells of about 40-mm outside diameter (OD) and 25-mm inside diameter (ID) were extruded 8:1 from a vacuum arc-melted ingot at 1900 and 1550 K. Two different OD tubes of approximately 0.36-mm wall thickness were fabricated from each tube shell by a series of 26 cold drawing operations with two in process anneals. The microstructure of tube shells and the tubing before and after a 2-step heat treatment were characterized. Residue extracted chemically from each sample was also analyzed to identify the precipitates. The results concerning the effect of the initial extrusion temperature and subsequent processing on the microstructure of the tubes are presented together with a review of results from similar work on Nb-1Zr-0.1C sheet stock.

Uz, Mehmet↗
NASA NTRS1996

Simultaneous Use Of Zr And Mg Anodes In XPS

Improved x-ray source for x-ray photoelectron spectroscopy (XPS) contains both zirconium anode with beryllium window and magnesium anode with aluminum window. Previously unresolvable peaks of electron-energy spectrum become resolvable. Developed specifically for use in analyzing distributions of chemical constituents in surface layers of specimens of 2219 aluminum alloy and in determining the depths of surface oxide layers and relative proportions of aluminum and oxide in layers. Also used to study chemical constituents of surface layers in other material systems - for example, thin oxide films on silicon-based semiconductor devices, oxide films on alloys, and surface layers affecting adhesion of paints or bonding materials.

Allgeyer, D. F.↗
NASA NTRS1996

Three-color resonance ionization spectroscopy of Zr in Si

As our society becomes technologically more complex, computers are being used in greater and greater numbers of high consequence systems. Giving a machine control over the lives of humans can be disturbing, especially if the software that is run on such a machine has bugs. Formal reasoning is one of the most powerful techniques available to demonstrate the correctness of a piece of software. When reasoning about software and its development, one frequently encounters expressions that contain partial functions. As might be expected, the presence of partial functions introduces an additional dimension of difficulty to the reasoning framework. This difficulty produces an especially strong impact in the case of high consequence systems. An ability to use formal methods for constructing software is essential if we want to obtain greater confidence in such systems through formal reasoning. This is only reasonable under automation of software development and verification. However, the ubiquitous presence of partial functions prevents a uniform application to software of any tools not specifically accounting for partial functions. In this paper we will describe a framework for reasoning about software, based on the nonstrict explicit domain approach, that is applicable to a large class of software/hardware systems. In this framework the Hoare triples containing partial functions can be reasoned about automatically in a well-defined and uniform manner.

Hansen, C. S.↗
NASA NTRS2002

X-Ray and Electrostatic Levitation Undercooling Studies in Ti-Zr-Ni Quasicrystals Forming Alloys

The first undercooling nucleation measurements of electrostatic-levitated droplets of TiZrNi alloys that form the icosahedral quasicrystal phase (i-phase) are presented. The reduced undercooling for crystallization decreases with an increasing polytetrahedral order of the primary solidifying phase, supporting the existence of a developing icosahedral short-range order in the undercooled liquid. X-ray diffraction measurements made at the Advance Photon Source on levitated liquid droplets of these alloys at their liquidus temperatures, however, show no evidence for increased icosahedral order. This suggests that significant ordering only occurs below the melting temperature.

Rogers, J. R.↗
NASA NTRS2001

A-site- and/or B-site-modified PbZrTiO3 materials and (Pb, Sr, Ca, Ba, Mg) (Zr, Ti, Nb, Ta)O3 films having utility in ferroelectric random access memories and high performance thin film microactuators

A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

Roeder, Jeffrey F.↗
NASA NTRS2004

A-SITE-AND/OR B-SITE-MODIFIED PBZRTIO3 MATERIALS AND (PB, SR, CA, BA, MG) (ZR, TI,NB, TA)O3 FILMS HAVING UTILITY IN FERROELECTRIC RANDOM ACCESS MEMORIES AND HIGH PERFORMANCE THIN FILM MICROACTUATORS

A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

Roeder, Jeffrey F.↗
NASA NTRS2017

Standards for Analysis of Ce, La, Pb, Rb, Se, Sr, Y, AND Zr in Rock Samples Using Laser-induced Breakdown Spectroscopy and X-ray Fluorescence

Analytical geochemistry has long depended on the availability of robust suites of rock standards with well-characterized compositions. Standard rock powders for wet chemistry and x-ray fluorescence were initially characterized and supplied to the community by the U.S. Geological Survey, which continues to distribute a few dozen standards. Many other rock standards have subsequently been developed by organizations such as the Centre de Recherches Pétrographiques et Géochimiques (CRPG) and Brammer Standard Company, Inc.

LIBS↗
NASA NTRS2016

Microstructural and Creep Properties of Boron- and Zirconium-Containing Cobalt-Based Superalloys

The effects of micro-additions of boron and zirconium on grain-boundary (GB) structure and strength inpolycrystalline γ(f.c.c.) plus γ’(L12) strengthened Co-9.5Al-7.5W-X at. % alloys (X=0-Ternary, 0.05B, 0.01B,0.05Zr, and 0.005B-0.05Zr at. %) are studied. Creep tests performed at 850 °C demonstrate that GB strength and cohesion limit the creep resistance and ductility of the ternary B- and Zr-free alloy due to intergranular fracture. Alloys with 0.05B and 0.005B-0.05Zr both exhibit improved creep strength due to enhanced GB cohesion,compared to the baseline ternary Co-9.5Al-7.5W alloy, but alloys containing 0.01B or 0.05Zr additions displayed no benefit. Atom-probe tomography (APT) is utilized to measure GB segregation, where B and Zr are demonstrated to segregate at GBs. A Gibbsian interfacial excess of 5.57 ± 1.04 atoms nm(exp) -2 was found for B at aGB in the 0.01B alloy and 2.88 ± 0.81 and 2.40 ± 0.84 atoms nm2 for B and Zr, respectively, for the 0.005B-0.05Zr alloy. The GBs in the highest B-containing (0.05B) alloy exhibit micrometer-sized boride precipitates with adjacent precipitate denuded-zones (PDZs), whereas secondary precipitation at the GBs is absent in theother four alloys. The 0.05B alloy has the smallest room temperature yield strength, by 6%, which is attributedto the PDZs, but it exhibits the largest increase in creep strength (with an ~2.5 order of magnitude decrease inthe minimum strain rate for a given stress at 850 °C) over the baseline Co-9.5Al-7.5W alloy.

Creep↗
NASA NTRS1973

Zirconium and hafnium abundances in some lunar materials and implications of their ratios

A new rapid and precise analytical procedure for Zr and Hf has been applied to the study of lunar materials. The results indicate that the Zr/Hf ratios in lunar materials vary in a narrow range from 36.6 to 51.3 while their respective contents vary by a factor of 40. There is a strong Zr, Hf, and major element correlation. This correlation and the Zr and Hf systematics suggest that lunar materials fall into two groups. One group characterized by high Zr and Hf contents and higher Zr/Hf ratios corresponds to materials with a high KREEP content; the other characterized by low Zr and Hf contents and lower Zr/Hf ratios corresponds to materials with high Ti, Fe, Mn, and Mg contents. We believe that the modest Zr and Hf fractionation we observe is related to the extent of stabilization of the metals in the early titanium minerals and a charge disparity under extremely reduced conditions in which Zr exists as 3+, while Hf remains as 4+.

Chyi, L. L.↗
NASA NTRS1978

Some properties of low-vapor-pressure braze alloys for thermionic converters

Density, dc electrical resistivity, thermal conductivity, and linear thermal expansion are measured for arc-melted rod-shaped samples of binary eutectics of Zr, Hf, Ru, Nb, Ir, Mo, Ta, Os, Re, and W selected as very-low-pressure braze fillers for thermionic converters. The first two properties are measured at 296 K for Zr-21.7 at% Ru, Zr-13 wt% W, Zr-19 wt% W, Zr-22.3 at% Nb, Nb-66.9 at% Ru, Hf-25.3 wt% Re, Zr-25.7 at% Ta, Hf-22.5 at% W, and Nb-35 wt% Mo. The last property is measured from 293 K to 2/3 melting point for specified alloys of different compositions. Resistivities of 0.000055 to 0.000181 ohm-cm are observed with the alloys having resistivities about ten times that of the less resistive constituent metal and about three times that of the more resistive constituent metal, except for Zr-19 wt% W and Nb-35 wt% Mo (greater resistivities). Thermal expansion coefficients vary from 0.000006 to 0.0000105/K. All brazes exhibit linear thermal expansion near that of their constituent metals.

Bair, V. L.↗