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It is shown that in Ni's theory of gravity, which is identical to general relativity in the post-Newtonian limit, neutron stars of arbitrarily large mass are possible. This result is independent, within reasonable bounds, of the equation of state of matter at supernuclear densities.
Fractography and metallographic sectioning were used to investigate the influence of microstructure and strength on the fracture toughness (KIc) and fracture mechanism of an 18 Ni, 300 grade maraging steel. Increased yield strength from 1442 to 2070 MN/m squared through precipitation hardening results in a KIc loss from 143 to 55 MN/m superscript 3/2. Ti (C,N) Ti2S, and TiC inclusions in sizes from 1 to 8, 1 to 15, and 0.1 to 2 microns respectively serve as sites for void nucleation and lead to fracture by the dimpled rupture process in all strength levels considered. TiC nucleated dimples occupy more than half the fracture in all conditions. Void nucleation rate and resultant number of dimples per unit area of fracture increase with increasing yield strength. Average dimple size decreases with increasing strength and/or overaging which follows from the decreasing amount of stable void growth measured by sectioning tensile specimens. Void growth is assisted by crack branching along a path of TiC inclusions. Coalescence occurs in the highest strength materials by a combination of TiC void nucleation and premature separation at strengthening precipitates.
The rationale and application of a plated metal system, Pd2Si Pd - Ni - solder, is presented. This metallization system is particularly useful on shallow p-n junction solar cells. The advantages of such plated solar cell contacts are discussed. A process sequence for applying the metallization system is outlined. A specific example is presented, including chemical plating solution formulations and detailed process step descriptions. Electrical test data for solar cells metallized with the palladium-nickel-solder system are provided.
The isothermal oxidation of Ni-14Cr-24Al-xZr-type alloys was performed in still air at 1100, 1150, and 1200 C for times up to 200 hr. The zirconium content of the alloys varied from 0-0.63 atom percent (a/o). The oxidized surfaces were studied by optical microscopy, X-ray diffraction, and scanning electron microscopy. The base alloy was an alumina former with the zirconium-containing alloys also developing some ZrO2. The addition of zirconium above 0.066 a/o increased the rate of weight gain relative to the base alloy. Due to oxide penetratio, the weight gain increased with Zr content; however, the scale thickness did not increase. The Zr did increase the adherence of the oxide, particularly at 1200 C. The delta W/A vs. time data fit the parabolic model of oxidation. The specific diffusion mechanism operative could not be identified by analysis of the calculated activation energies. Measurements of the Al2O3 scale lattice constants yielded the same values for all alloys.
An RF-sputtered chrome oxide coating with metallic binders was developed. The chrome oxide coating has high-temperature capabilities and is wear resistant, and has some self-lubricating properties. A nichrome metallic binder was added in the coating to improve its ductility without significant loss in the hardness. The sputtering parameters were optimized to obtain a smooth coating with the maximum adherence. The coatings were applied using bias-sputter and sputter-deposit modes on the heat treated and annealed foil substrates. The coating applied on annealed foils using the sputter-deposit mode was smooth and had the best adherence. Metallurgical examinations showed that the coating was Ni-Cr + Cr2O3. The coating as applied was amorphous and it crystallized during substrate heat treatment.
Important requirements for protective coatings of Ni-Cr-Al alloys for gas turbine superalloys are resistance to oxidation accompanied by thermal cycling, resistance to thermal fatigue cracking. The resistance to oxidation accompanied by thermal cycling is discussed. The resistance to thermal fatigue cracking is also considered.
The reduction in the use of Cr in Ni base superalloys by the combined approaches of both elemental substitution and rapid solidification processing is studied. The elements Si, Zr, Y and Hf were chosen as potential partial substitutes for Cr in Waspaloy and IN 713LC sine their separate addition to other alloys has previously resulted in enhanced oxidation resistance. The roles of Cr and these replacement elements in determining the microstructure and properties are evaluated. The elements Si, Zr, and Y and Hf are used as partial replacements for Cr in the base superalloys and these resultant alloys are processed using rapid solidification techniques. The mechanical properties and oxidation resistance of the processed materials are evaluated. The microstructure is characterized using state of the art techniques (e.g. analytical transmission electron microscopy), and the mechanism by which these structures are produced is determined.
The FeMnAlC alloys may hold potential as Cr-free replacements for high strategic material iron base superalloys, but little is known about their intermediate temperature (650 C to 870 C) mechanical properties. The effects of alloying elements on the mechanical properties of model FeMnAlC alloys were studied. Results showed that modified FeMnAlC alloys had promising short term, intermediate temperature properties but had relatively poor stress rupture lives at 172 MPa and 788 C. Room temperature and 788 C tensile strength of FeMnAlC alloys were better than common cast stainless steels. Changes in room temperature tensile and 788 C tensile strength and ductility, and 788 C stress rupture life were correlated with changes in Ni, Mo, Ti, and Si levels due to alloying effects on interstitial carbon levels and carbide morphology. Fe-25Mn-5Al-2C had a very poor stress rupture life at 172 MPa and 788 C. Addition of carbide-forming elements improved the stress rupture life.
The probability of Ni-Cd battery survival was determined by researching survival data on cells fabricated from 1964-1977. A log of cell failure times were plotted against cumulative failure percentage and mean and standard deviation were determined.
Nickel-poor Fe-Ni grains smaller than 2.0 microns are common inclusions in ordinary, unequilibrated chondrites' porphyritic chondrule olivine, where the olivine grains seem to be relicts that survived chondrule formation without melting. This 'dusty' metal, whose most common occurrence is in the core of olivine grains having clear, Fe-poor rims, appears to be the product of the in situ reduction of FeO from the host olivine, with H2 or carbonaceous matter being the most likely reductants. H2 may have been implanted by solar wind or solar flare irradiation, but this requires the dissipation of nebular gas before the end of the chondrule formation process. Carbonaceous matter may have been implanted by shock. The large relict olivine grains may be nebular condensates or fragments broken from earlier chondrule generations.
Trace and minor element distributions in the iron meteorites are generally ascribed to partitioning during solidification of the parent body core or to partial melting within the parent body. A model involving fractional crystallization is considered. The model cannot account for differences between the measured values for the slopes on the log Ir-log Ni plots and the slopes predicted using experimentally determined distribution coefficients obtained in an investigation conducted by Goldstein and Friel (1978). The model has also other weaknesses. Part of the answer concerning the existing problems was provided by Narayan and Goldstein (1981, 1982). The present investigation is concerned with a further clarification of the effect of the minor elements P, S, and C on the distribution behavior of trace elements. Attention is given to measurements of the distribution coefficients for various elements (Ir, Ge, Ga, Au, Cu, Cr) in the presence of these minor elements.
A study has been made of the effect of supercooling, quenching rate, growth inhibitors, and grain refiners on the structure of levitation-melted Fe- 25 pct Ni alloys. A combination of three morphologies, dendritic, spherical, and mixed dendritic and spherical, is observed in samples superheated or supercooled by less than 175 K. At larger supercooling, however, only the spherical morphology is observed. The grain size and the grain boundary shape are found to be strongly dependent on the subgrain morphology but not on the quenching temperature. Considerable grain growth is evident in samples with spherical and mixed morphologies but not in the dendriitic samples. The average cooling rates during solidification and the heat transfer coefficients at the metal-quenching medium boundary are calculated. For samples solidified in water, molten lead, and ceramic molds, the heat transfer coefficients are 0.41, 0.52, and 0.15 w/sq cm, respectively.
Nickel-base superalloys are used in jet engine components such as disks, turbine blades, and vanes. Improvements in the fatigue behavior will allow the life to be extended or the payloads to be increased. The first part of the present investigation deals primarily with the effects of microstructural variations on the fatigue crack propagation (FCP) behavior of nickel-base alloys, while the second part is concerned with low-cycle fatigue (LCF) behavior of Ni base systems. Waspaloy at low temperature is considered, taking into account material heat treatment and test procedures, a composite plot of Waspaloy FCP data, Paris law fatigue crack propagation constants, monotonic tensile data, and overload FCP test results for Waspaloy. It is found that the FCP and overload behavior of nickel-base alloys may be markedly improved by heat treating. Attention is given to effects of cyclic deformation on microstructure and substructure, environmental damage, and an environmental/deformation model of high temperature LCF.
The corrosion of nickel base superalloy, U-700, by molten Na2MoO4 was studied in the temperature range of 750 deg to 950 deg C. After an induction period, the rate of corrosion is linear and catastrophic corrosion is observed. It is shown that the induction period is associated with the attainment of a minimum MoO3 activity in the melt, which corresponds to the equilibrium MoO3 activity for the reaction, 2MoO3(l) + Mo = 3MoO2(s). A mechanism is proposed to describe the catastrophic nature of corrosion, which involves transport of Ni++ through the melt resulting in formulation of NiO at the melt gas interface and basic fluxing of Cr2O3. The effect of the amount of Na2MoO4 on the corrosion kinetics was also studied. It is found that evaporation and the thermodynamic calculations for the Na2MoO4 - MoO3 system the activity of MoO3 is reduced considerably when dissolved in Na2MoO4, which causes a sharp decrease in the rate of evaporation of MoO3 from a Na2MoO4 - MoO3 melt.
An ongoing research program aims to characterize the solidification of several Ni- and Co-based commercial wrought type alloys. The techniques used and the data items sought are: (1) thermal analysis, liquidus, nonequilibrium solidus as a function of cooling rate, secondary reactions temperatures, incipient melting, progress of solidification as a function of temperature; (2) optical metallography, characteristic structures and secondary dendrite arm spacing as a function of cooling rate; (3) X-ray diffraction, identification of precipitates; and (4) SEM/EDAX, measure of microsegregation.
Samples of Pd(40)Ni(40)P(20) glass, produced by cooling the melt at 1 or 800 K/s, are heated in a differential scanning calorimeter to determine the crystallization kinetics. Optical microscopy shows that eutectic crystallization proceeds both by growth from the surface of the samples and by the growth of spherical regions around preexisting nuclei in the interior. A modified Kissinger (1957) analysis is used to obtain the activation energy for crystal growth (3.49 eV). The steady state homogeneous nucleation frequency at 590 K is about 10 million/cu m per sec. This is estimated to be the maximum nucleation frequency: it is too low to account for the observed population of quenched-in nuclei, which are therefore presumed to be heterogeneous. The major practical obstacle to glass formation in this system is heterogeneous nucleation.
Fifty Ni-base superalloys with concentrations of Cr, Al, Ti, Mo, W, Ta, and Cb systematically varied between two nonzero levels, were tested for cyclic oxidation resistance at 1100 and 1150 C. Oxidation resistance was interpreted in terms of the rate of specific weight change and the types of oxides formed. It is found that the resistance of the alloys to cyclic oxidation is largely determined by Al content, with a sharp increase in the oxidation resistance observed in the Al concentration range 5-8 at. pct. The effects of the other elements studied were small compared with that of aluminum. Best oxidation resistance characteristics were predicted for high Al (13 at. pct), low Cr (10 at. pct), low Ti (2 at. pct), low Cb (1 at. pct), and high Mo, W, and Ta (3 at. pct each). The effects of the refractory metals, however, are somewhat ambiguous and should be investigated further. Higher boron contents, which were unintentionally varied, were clearly detrimental even for the most resistant compositions.
A performance assessment is made for the Viking Mars Lander Program's sealed, sterilizable, 8-ampere hour Ni-Cd batteries, which use a nonwoven polypropylene separator material. Attention is given to separator wettability, the optimization of electrolyte quantity, and the reduction of plate carbonate, in view of thermal considerations and other environmental design and test requirements generated by mission characteristics. Life data based on mission experience identify, in addition to performance and degradation behavior, a series of shallow discharge reconditioning cycles and an intensive program of deep discharge reconditioning.