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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Mechanical properties of electron-beam-melted molybdenum and dilute molybdenum-rhenium alloys

A study of molybdenum and three dilute molybdenum-rhenium alloys was undertaken to determine the effects of rhenium on the low temperature ductility and other mechanical properties of molybdenum. Alloys containing 3.9, 5.9, and 7.7 atomic percent rhenium exhibited lower ductile-brittle transition temperatures than did the unalloyed molybdenum. The maximum improvement in the annealed condition was observed for molybdenum - 7.7 rhenium, which had a ductile-brittle transition temperature approximately 200 C (360 F) lower than that for unalloyed molybdenum. Rhenium additions also increased the low and high temperature tensile strengths and the high temperature creep strength of molybdenum. The mechanical behavior of dilute molybdenum-rhenium alloys is similar to that observed for dilute tungsten-rhenium alloys.

Klopp, W. D.↗
NASA NTRS1977

X-ray photoelectron spectroscopy study of radiofrequency sputtered chromium bromide, molybdenum disilicide, and molybdenum disulfide coatings and their friction properties

Radiofrequency sputtered coatings of CRB2, MOSI2, and MOS2 were examined by X-ray photoelectron spectroscopy. The effects of sputtering target history, deposition time, RF power level, and substrate bias on film composition were studied. Friction tests were run on RF sputtered surfaces of 440-C steel to correlate XPS data with lubricating properties. Significant deviations from stoichiometry and high oxide levels for all three compounds were related to target outgassing. The effect of biasing on these two factors depended on the compound. Improved stoichiometry correlated well with good friction and wear properties.

Wheeler, D. R.↗
NASA NTRS1988

Lubricating properties of molybdenum disulfide. Part 3: Performance of molybdenum disulfide-containing oils in fluid lubrication

The lubricating properties of a straight mineral oil with and without MoS2 powder were studied. Bearing testers of thrust-collar type and of journal bearing type were used for thin- and fluid-film conditions, respectively. The effectiveness of the MoS2 powder in the oil differed depending on the conditions of the rubbing surfaces. For fluid film conditions, considerable effects of the MoS2 were observed, in contrast to the thin-film cases. The addition of MoS2 powder was effective only when the lubricant film was formed between surfaces thickly enough to allow the inflow of MoS2 particles.

Soda, Norimune↗
NASA NTRS1987

Chill block melt spinning of nickel-molybdenum alloys

Samples of Ni-Mo alloys ranging in composition from pure nickel to Ni-40 at. pct molybdenum were cast by the chill block melt-spinning rapid solidification technique and examined by optical metallography, X-ray diffraction, and microhardness testing. Casting difficulties were encountered with lean alloys, but richer alloys spread more readily on the casting wheel. Alloy microstructures for 5 to 37.5 at. pct molybdenum ribbons were primarily cellular/dendritic; microstructure feature size decreased with increasing molybdenum content. Extended solubility of molybdenum in gamma-nickel, with fcc lattice parameter increasing with composition to the 1.05 power, was observed up to 37/5 at. pct molybdenum. Substoichiometric Ni-Mo (delta) nucleated on the wheel side of the ribbons of compositions 35, 37.5, and 40 at. pct molybdenum. The amount of partitionless delta-phase thus formed increased with increasing molybdenum content and quench rate. This substoichiometric delta transformed readily to a fine structure gamma-delta mixture.

Hemker, Kevin J.↗
NASA NTRS1959

Tensile Properties of Molybdenum and Tungsten from 2500 to 3700 F

Specimens of commercially pure sintered tungsten, arc-cast unalloyed molybdenum, and two arc-cast molybdenum-base alloys (one with 0.5 percent titanium, the other with 0.46 percent titanium and 0.07 percent zirconium) were fabricated from 1/2-inch-diameter rolled or swaged bars. All specimens were evaluated in short-time tensile tests in the as-received condition, and all except the molybdenum-titanium-zirconium alloy were tested after a 30-minute recrystallization anneal at 3800 F in a vacuum of approximately 0.1 micron. Results showed that the tungsten was considerably stronger than either the arc-cast unalloyed molybdenum or the molybdenum-base alloys over the 2500 to 3700 F temperature range. Recrystallization of swaged tungsten at 3800 F considerably reduced its tensile strength at 2500 F. However, above 3100 F, the as-swaged tungsten specimens recrystallized during testing, and had about the same strength as when recrystallized at 3800 F before evaluation. The ductility of molybdenum-base materials was very high at all test temperatures; the ductility of tungsten decreased sharply above about 3120 F.

Hall, Robert W.↗
NASA NTRS1972

Alloy hardening and softening in binary molybdenum alloys as related to electron concentration

An investigation was conducted to determine the effects of alloy additions of hafnium, tantalum, tungsten, rhenium, osmium, iridium, and platinum on hardness of molybdenum. Special emphasis was placed on alloy softening in these binary molybdenum alloys. Results showed that alloy softening was produced by those elements having an excess of s+d electrons compared to molybdenum, while those elements having an equal number or fewer s+d electrons that molybdenum failed to produce alloy softening. Alloy softening and alloy hardening can be correlated with the difference in number of s+d electrons of the solute element and molybdenum.

Stephens, J. R.↗
NASA NTRS1986

The role of oxygen in porous molybdenum electrodes for the alkali metal thermoelectric converter

A model for chemical reactions in porous molybdenum electrodes is presented which is based on thermochemical and kinetic data, known sodium-molybdenum-oxygen chemistry, X-ray diffraction analysis of molybdenum and molybdenum oxide electrodes, and the electrochemical behavior of the cell. Enhanced sodium transport through the electrode in its optimum performance state is found to be due to the high sodium ion conductivity of molten Na2MoO4 in the pores, and the electrical conduction to the molybdenum matrix by Na2Mo3O6. The decline of electrode performance is shown to be due to a combination of loss mechanisms for the Na-Mo-O compounds including reduction at short circuit, disproportionation of Na2Mo3O6 at open circuit, and the evaporation of Na2MoO4 at elevated temperature. It is suggested that operation of the cell at moderate voltage of about 0.5 V corresponding to maximum power may be a more stable condition for the porous electrode than open-circuit stand or short-circuit, where degradation reactions are heightened.

Williams, R. M.↗
NASA NTRS1953

Survey of Portions of the Chromium-Cobalt-Nickel-Molybdenum Quaternary System at 1,200 Degrees C

A survey was made of portions of the chromium-cobalt-nickel-molybdenum quaternary system at 1,200 degrees c by means of microscopic and x-ray diffraction studies. Since the face-centered cubic (alpha) solid solutions form the matrix of almost all practically useful high-temperature alloys, the solid solubility limits of the quaternary alpha phase were determined up to 20 percent molybdenum. The component cobalt-nickel-molybdenum, chromium-cobalt-molybdenum, and chromium-nickel-molybdenum ternary systems were also studied. The survey of these systems was confined to the determination of the boundaries of the face-centered cubic (alpha) solid solutions and of the phases coexisting with alpha at 1,200 degrees c.

Rideout, Sheldon Paul↗
NASA NTRS1971

Molybdenum-UO2 cermet irradiation at 1145 K.

Two molybdenum-uranium dioxide cermet fuel pins with molybdenum clad were fission-heated in a forced-convection helium coolant for sufficient time to achieve 5.3% burnup. The cermet core contained 20 wt % of 93.2% enriched uranium dioxide. The results were as follows: there was no visible change in the appearance of the molybdenum clad during irradiation; the maximum increase in diameter of the fuel pins was 0.8%; there was no migration of uranium dioxide along grain boundaries and no evident interaction between molybdenum and uranium dioxide; and, finally, approximately 12% of the fission gas formed was released from the cermet core into the gas plenum.

Mcdonald, G.↗