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Johnson, W. L.

Publications and source records attributed to Johnson, W. L..

48 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

A conceptual approach for noncontact calorimetry in space

A concept is developed and described which allows to measure the heat capacity and the effective thermal conductivity of stable and undercooled liquid metals and alloys in an electromagnetic levitation apparatus. A proposal is made to use an ac pulse heating method which is used nowadays as a standard technique for precision measurement of low-temperature heat capacities. The ideal process parameters, including the drop diameter D, temperature T, and frequency of measurement omega, can be optimized when the following relations hold for the external and internal relaxation time constants tau-1 and tau-2, respectively: omega(tau-1) greater than 10 and omega(tau-2) less than 0.1. Then, heat capacity data can be obtained with an accuracy of better than 1 percent with D about 5 to 10 mm, T between 1200 and 1800 K, and omega between 0.1 and 1 Hz for typical metals and alloys.

Fecht, H. J.↗
NASA NTRS1985

Refractory amorphous metallic (W/0.6/ Re/0.4/)76B24 coatings on steel substrates

Refractory metallic coatings of (W/0.6/ Re/0.4/)76B24 (WReB) have been deposited onto glass, quartz, and heat-treated AISI 52100 bearing steel substrates by dc magnetron sputtering. As-deposited WReB films are amorphous, as shown by their diffuse X-ray diffraction patterns; chemically homogeneous, according to secondary ion mass spectrometry (SIMS) analysis; and they exhibit a very high (approximately 1000 C) crystallization temperature. Adhesion strength of these coatings on heat-treated AISI 52100 steel is in excess of approximately 20,000 psi and they possess high microhardness (approximately 2400 HV50). Unlubricated wear resistance of such hard and adherent amorphous metallic coatings on AISI 52100 steel is studied using the pin-on-disc method under various loading conditions. Amorphous metallic WReB coatings, about 4 microns thick, exhibit an improvement of more than two and a half orders of magnitude in the unlubricated wear resistance over that of the uncoated AISI 52100 steel.

Thakoor, A. P.↗
NASA NTRS1984

Corrosion behavior of magnetron sputter-deposited (Mo/0.6/Ru/0.4/)82B18 and Mo82B18 amorphous metal films

Amorphous metallic films of Mo49Ru33B18 and Mo82B18 have been prepared by magnetron sputtering, and their corrosion behavior was investigated and compared with amorphous liquid-quenched Mo49Ru33B18 and crystalline Mo i acidic and basic solutions. Sputtered Mo49Ru33B18 showed lower corrosion rates compared with liquid-quenched Mo49Ru33B18, owing to the superior surface smoothness and uniformity of the former. Amorphous Mo82B18 showed low corrosion rates in both acidic and basic aqueous solutions. Comparison of the corrosion properties of Mo49Ru33B18 with Mo82B18 and Mo demonstrates the roles of the alloys' constituents. Ru significantly extends the passive region to high-anodic potentials, but, at less-anodic potentials, Mo82B18 has the lowest corrosion rate.

Williams, R. M.↗
NASA NTRS1984

Containerless Solidification of Amorphous Metals

Method produces large amorphous alloys. Spheres of amorphous metal alloys formed and collected after molten samples coated and cooled in drop tube. Coated spheres cooled acoustically and cryogenically. Amorphous specimens 5mm in diameter or larger possible.

Lee, M. C.↗
NASA NTRS1983

NMR studies of electronic structure in crystalline and amorphous Zr2PdH/x/

The proton Knight shifts and spin-lattice relaxation times have been measured in crystalline and amorphous Ze2PdH(x). Core polarization from the Zr d-band dominates the proton hyperfine interactions. The density of Fermi level d-electron states is reduced in the amorphous phase relative to the electron density in crystalline Zr2PdH(x).

Bowman, R. C., Jr.↗
NASA NTRS1983

Use of Landsat data to predict the trophic state of Minnesota lakes

Near-concurrent Landsat Multispectral Scanner (MSS) and ground data were obtained for 60 lakes distributed in two Landsat scene areas. The ground data included measurement of secchi disk depth, chlorophyll-a, total phosphorous, turbidity, color, and total nitrogen, as well as Carlson Trophic State Index (TSI) values derived from the first three parameters. The Landsat data best correlated with the TSI values. Prediction models were developed to classify some 100 'test' lakes appearing in the two analysis scenes on the basis of TSI estimates. Clouds, wind, poor image data, small lake size, and shallow lake depth caused some problems in lake TSI prediction. Overall, however, the Landsat-predicted TSI estimates were judged to be very reliable for the secchi-derived TSI estimation, moderately reliable for prediction of the chlorophyll-a TSI, and unreliable for the phosphorous value. Numerous Landsat data extraction procedures were compared, and the success of the Landsat TSI prediction models was a strong function of the procedure employed.

Lillesand, T. M.↗
NASA NTRS1983

Structural difference rule for amorphous alloy formation by ion mixing

A rule is formulated which establishes a sufficient condition that an amorphous binary alloy will be formed by ion mixing of multilayered samples when the two constituent metals are of different crystalline structure, regardless of their atomic sizes and electronegativities. The rule is supported by the experimental results obtained on six selected binary metal systems, as well as by the previous data reported in the literature. The amorphization mechanism is discussed in terms of the competition between two different structures resulting in frustration of the crystallization process.

Liu, B.-X.↗
NASA NTRS1982

A two-dimensional phase separation on the spherical surface of the metallic glass Au55Pb22.5Sb22.5

Recent experiments indicate that a phase separation in a spherical sample of the metallic glass Au55Pb22.5Sb22.5 occurs near the surface of the sphere. This strongly suggests either a contribution of surface-free energy to the decomposition process or a possible influence of near surface impurities absorbed during synthesis of the sphere. The surface phase separation has been studied as a function of cooling rate of the sphere. At high cooling rates (small sphere sizes), the surface separation disappears altogether suggesting that the surface of the parent liquid droplet is initially homogeneous.

Lee, M. C.↗
NASA NTRS1982

Spheres of the metallic glass Au55 Pb22.5 Sb22.5 and their surface characteristics

Spheres of the metallic glass Au55 Pb22.5 Sb22.5 have been formed up to a size of approximately 1.5 mm in diameter. X-ray diffraction was used to establish the glassy nature of the samples and to provide evidence of two phase-separated glass regions. Scanning electron microscopy provided a direct visual observation of the two-phase amorphous network on the surface of the sphere. The physical dimensions of the phase-separated regions were observed to be cooling-rate sensitive. Energy dispersive spectroscopy indicated that the compositions of these two glassy phases were Au-rich and Pb-rich, respectively, confirming the results of Kim and Johnson (1981). In addition, the spheres exhibited an unusual surface smoothness of better than + or - 250 A

Lee, M. C.↗
NASA NTRS1982

Investigation of metallic and metallic glass hollow spheres for fusion target application

The first successful formation of submillimeter and millimeter spherical shells of tin and of a gold-lead-antimony alloy by means of the hollow-jet instability technique developed by Kendall is reported. Examination of tin specimens by SEM reveals that surface quality varies from poor to excellent. Whereas the metal is employed only as a convenient and inexpensive material, the gold alloy is important in that it is hard, has a high atomic number, and may be solidified into the amorphous state through the provision of a modest cooling rate. AuPbSb spherules up to 1.5 mm in diameter are produced using LN2 or chilled methanol as a coolant. It is found that these amorphous samples possess a superb surface smoothness compatible with fusion target requirements. It is noted that hollow spheres currently made of this alloy have an average outside diameter of 2000 microns.

Lee, M. C.↗