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The copper alloyNARloy-Z (Cu-3Ag-0.5Zrwt%)has goodpotential for high heat  ux structural applications in hypersonic vehicles because of its high thermal conductivity and high-temperature strength. However, it is subject to severe oxidationat temperatures where it might be used. A Cu-30 vol%Cr protective coating produced by lowtemperature arc vapor deposition was evaluated under dynamic oxidation in an electric arc-heated wind tunnel. The emittance of the coating is greater than the emittance of the alloy, and the recombination efŽ ciency of the coating is typical of values encountered with metal alloys and metallic oxides. The coating protects the alloy under dynamic oxidation conditions, with specimens gaining less than 1 mg/cm2 over a 10-h exposure period. Protection of the alloy from oxidation results from a continuous layer of Cr2O3 that it is partially shielded from the hostile dynamic oxidation/atomic oxygen environment by a layer of CuO.

A method is presented for determining the recombination efficiency of coatings for hypersonic vehicle applications. The approach uses experimental results from arc-jet tests with an analysis to determine the efficiency for the recombination of atomic species present in the boundary layer. The analysis employs analytical solutions to the laminar boundary-layer heat-transfer equations with experimental heating-rate, temperature, and pressure measurements. The authors discuss experimental difficulties in achieving reliable materials-performance data. The utility of the method is that it provides a rapid and efficient tool for use in qualitative screening and development of materials. The effects of second-order heat-transfer terms may be as high as 50% for low-catalysis surfaces. With the second-order terms included, the maximum uncertainty in recombination-efficiency data for low-catalysis surfaces is 45%. The discussions are based on experimental data and calculations for arc-jet tests of the titanium alloy Ti-14Al-21Nb with a borosilicate-like glass coating that has a recombination efficiency of about 0.006 to 0.01. 20 refs.

Molybdenum-based alloys have the potential for meeting the materials requirements of many applications requiring strength values as high as 140 MPa at temperatures as high as 1,300 C. The addition of Re to Mo provides greater ductility and a lower ductile-to-brittle transition temperature than for unalloyed Mo. The alloy Mo-47Re (wt %) is one alloy from the Mo-Re system that is a candidate for use in hydrogen-fueled engines of hypersonic vehicles. Potential applications for the alloy in engines include heat exchanger tubes at temperatures up to 1,260 C and combustion chamber linings at temperatures to 1,370 C and hydrogen pressures to 175 ATM. The projected service life at peak temperature in such an application is about 12 h. Because of the reactivity of molybdenum and rhenium with oxygen in air at high temperatures, some means of protecting the alloy must be devised. One approach to protecting the alloy is to clad it with a non-reactive impermeable barrier layer. Platinum is proposed as a candidate for use as a cladding because of its high melting point (1,790 C) and chemical stability at high temperature. This paper presents results from a study of the oxidation performance of Pt-clad Mo-47Re. Pt-clad samples weremore » tested under static and dynamic oxidation conditions at 1,260 C. A single unclad sample was tested under dynamic oxidation conditions at 595 C. The static oxidation tests were conducted in an ambient pressure furnace with laboratory air. The dynamic oxidation tests were conducted in an electric arc-heated wind tunnel. Weight change, metallography, and microscopy results are presented to show the effects of oxidation on the alloy and interaction between the cladding and the alloy.« less

Use is made of the thermogravimetric-analysis method to ascertain the hydrogen-transport characteristics of the Timetal-21S beta-Ti alloy, at pressures of up to 50 torr over the 400-800 C temperature range. Hydrogen solubility is found to be high; the equilibrium hydrogen concentration is noted to deviate from Sievert's law at higher pressures. These deviations are likely associated with hydrogen-induced microstructural changes in the alloy, and the kinetics of hydrogen uptake reflect these changes.

Static oxidation kinetics of Ti-25Al-10Nb-3V-1Mo (atomic percent) were investigated in air over the temperature range of 650–1000°C using thermogravimetric analysis. The oxidation kinetics were complex at all exposure temperatures and displayed up to two distinct stages of parabolic oxidation. Breakaway oxidation occurred after long exposure times at high temperatures. Oxidation products were determined using x-ray diffraction techniques, electron microprobe analysis, and energy dispersive x-ray analysis. Oxide scale morphology was examined using scanning electron microscopy of the surfaces and cross-sections of oxidation specimens. The oxides during the parabolic stages were compact and multilayered, consisting primarily of TiO2 doped with Nb, a top layer of Al2O3 and a thin bottom layer of TiN. The transition between the first and second parabolic stage is linked to the formation of a TiAl layer at the oxide-metal interface. Porosity also formed in the TiO2 layer during the second stage, causing degradation of the oxide and breakaway oxidation.

Results are presented from an AES investigation of the surface characteristics of pure Ti, Ti-14Al-21Nb (alpha-2 aluminide), and Ti-33Al-6Nb-1.4Ta (gamma aluminide) under ultrahigh vacuum conditions over the 20-1000 C temperature range. The observed variations in surface composition are noted to be dramatic and indicative of a direct relationship between the amount of retained oxygen and carbon on the surface and the quantity of Al in that surface's vicinity. While TiO2 was the main surface oxide for pure Ti and the alpha-2 and gamma aluminides, only metallic peaks were observable at 600 C; at 1000 C, metallic Al and Ti were observed.

The effect of temperature, at conditions of ultrahigh vacuum, on the surface composition of the Ti-14Al-21Nb (in wt pct) alloy was investigated in samples heated to 1000 C in 100 C increments. Results of AES spectroscopy revealed that the Ti-14Al-21Nb alloy surface is extremely sensitive to temperature. At 300 C, the carbon and oxygen began to rapidly dissolve into the alloy, and at 600 C, bulk S segregated to the surface. The variation in the surface composition was extensive and different over the temperature range studied, indicating that there may be substantial changes in the hydrogen transport.

CVD coatings of boron-oxygen-silicon and aluminum-boron-oxygen and silicon compositions were applied to alpha 2 and gamma titanium-aluminide alloys, and tested under simulated earth reentry conditions to evaluate oxidation protection, recombination effifiency and total emittance under cyclic exposures between temperatures of 300 and 1255 K. The degree of oxidation protection afforded to the alloys was evaluated from the amount of specimen weight gain after a 100 hour exposure to air at atmospheric pressure and at a temperature of 1255 K. Data are presented for two types of coatings, a monolithic and a multilayer, which have recombination efficiencies from 0.005 to 0.020 after ten one-half hour long simulated reentry cycles. Total normal emittance was 0.80 or greater and weight gain was less than 10 g/sq m both coating types. Compositional and morphological changes resulting from the exposures are discussed in relation to time-dependent variations in recombination efficiency.

A program is presented that removes broadening from X-ray diffraction spectra. An instrumental spectrum can be used to describe empirically the broadening to be removed, or a Gaussian, Cauchy, or Pearson-VII distribution can be used to analytically describe it. In either case, singlet or doublet forms can be generated. The program returns the deconvoluted spectrum, the reconstructed spectrum, and a sum-of-squares difference between the original and reconstructed spectra. Deconvolution is accomplished using a combination of least-squares, background, and smoothing criteria that minimizes the effect of random counting errors.

The oxidation kinetics of commercial purity Ti-A55 exposed to laboratory air in the 593-760 C temperature range were continuously monitored by thermogravimetric analysis. The oxide thickness was measured by microscopy, and the substrate contamination was estimated from microhardness measurements. The microhardness depth profiles were converted to oxygen composition profiles using calibration depth. The oxygen diffusion coefficient in alpha-Ti appears to be approximately concentration-independent in the 1-10 at. pct oxygen range. Diffusion coefficient for oxygen in TiO2 has been estimated as a function of temperature and is found to be about 50 times the value in alpha-Ti. The metallographically prepared cross sections of the oxidized specimens revealed a 'moving boundary' in the substrate, parallel to the oxide-metal interface. This boundary was associated with a specific oxygen level of 5.0 + or - 0.5 at. pct. It occurred at a distance from the oxide-metal interface which was correlatable with temperature and time of exposure. The diffusion coefficient corresponding to the composition of this moving boundary is in excellent agreement with the effective diffusion coefficient for the substrate contamination.

Statically oxidized Inconel 617 and MA 956 superalloys were prepared with vapor deposited aluminosilicate layers and exposed to temperatures which simulated reentry conditions. The aluminosilicate layers were 1-2 microns thick. The trials consisted of exposures to 1500-2300 F heat while surface temperatures were monitored with pyrometers. Analyses were then performed of the catalytic activity, oxidation phenomena, and radiative properties after thermal cycling the specimens for 8 hr. Both alloys were found to be catalytic to the recombination processes of dissociated species in the reentry environment. The coatings reduced the catalytic activity by 40 percent for both alloys but did not change the emittance. An enhanced Cr depletion zone was detected in the Inconel samples, implying that the coating did not prevent diffusion loss of Cr. The coated MA 956, on the other hand, gained weight over the course of the trials.

Ti-6Al-2Sn-4Zr-2Mo titanium alloy is a candidate material for multiwall thermal protection system concepts for advanced space transportation system vehicles. The total oxidation kinetics for this alloy, exposed to laboratory air in the 593–760°C range, were monitored by thermogravimetric analysis. The oxide thickness was measured by microscopy and the substrate contamination was estimated from microhardness measurements. Tensile elongation was determined for selected foil specimens after exposure to simulated space shuttle reentry conditions. The variation of total weight gain with time was found to have two distinct parabolic stages separated by a transient region. This transient was due to a process which involved an increase in the parabolic growth rate constant for the oxide and a simultaneous increase in oxygen solubility at the oxide metal interface. The time dependent increase in oxygen solubility at the interface was from about 7 at. % in stage 1 to about 18 at. % in stage 2. The diffusion coefficient for oxygen in the alloy was determined as a function of temperature using the difference between the total weight gain in stage 1 and the corresponding weight gain due to oxide growth. A model for the total oxidation kinetics, accounting for the two individual components namely oxide growth and solid solution formation, is proposed. The activation energy for the diffusion of oxygen in the alpha-solid solution is shown to be roughly equal to the activation energy for the degradation of tensile elongation for the alloy in the foil gage condition.

An improved deconvolution theory is presented for the resolution enhancement in powder diffraction spectra. In powder patterns, diffracted intensity, which is conceptually located at a single 2θ position, is actually distributed over a range of 2θ because of instrumental factors, crystal defects, beam penetration, and sample flatness. The location of the peak is usually taken as the peak maximum or the peak centroid. However, when interpreting complex spectra these approaches to locating peaks are not straightforward and deconvolution can be a useful tool. The method presented herein enhances resolution without altering peak area or peak position. Comparisons are made with results of other methods, with emphasis on deconvoluting spectra that contain random error. The discussion includes treatment of discrete data and analysis of the properties of the solution.

Inconel 617 is a nickel-based superalloy being considered for heat-shield applications because of its hightemperature strength, good oxidation resistance, and high emittance of oxidized surfaces. While the effects of simulated re-entry conditions on emittance and oxidation of Inconel 617 have been studied, the combined effects of the ground-based environment with sea salt exposure and the re-entry environment have not been evaluated. Experimental results are presented to show the effects of environmental simulation including ground-based and re-entry exposure on the emittance and oxidation of Inconel 617. Specimens were exposed to simulated re-entry at a surface temperature of 1370 K in the Langley Research Center Hypersonic Materials Environmental Test System Facility with and without alternate exposures to an atmospheric seashore environment or a laboratory sea salt environment. This paper presents emittance, mass loss, oxide chemistry, and alloy composition data for the specimens.

The viability of using coated Ti-6Al-2Sn-4Zr-2Mo foils at 620°C in air was established through mechanical and thermogravimetric testing. Weight-grained and oxygen embrittlement were significantly reduced by the coatings. The residual tensile elongation of coated specimens was 2.5 times that of uncoated specimens. Comparison depth-profiling with X-ray diffraction verified the reduction of oxygen solid-solution in the α-phase for a selection of coated specimens.

A binary lattice gas model is described whose properties can be exactly transformed into those of a reference one‐component lattice gas. The model lattice contains regular lattice sites occupied by one component and decorated bond sites occupied by the second component. Multiple occupancy of sites is not allowed. All other interactions between like molecules are zero but there is a finite repulsion between unlike nearest neighbors. The complete two‐phase region of the binary system is described by means of the two‐phase behavior of the reference system. The two‐phase region in a constant temperature plane is enclosed in a closed‐loop binodal curve with two plait points. The binodal curve near the plait point is found to be of degree (1‐α′) / β while the degree of the top of the coexistence surface is 1 / β, where α′ and 1 / β are the exponents of the divergence of the constant volume heat capacity in the two‐phase region and the degree of the coexistence curve, respectively, of the reference system. The h...

The contributions of the chain length, chain structure, internal rigidity, segment potential function, and “combinatorial” configurational entropy to the properties of liquid short-chain molecules and their mixtures, as exemplified by the polyphenyl series, are all shown to be significant in terms of general models of simple chain molecules such as those of Prigogine and co-workers and of Flory. The molecular parameters of these systems can be characterized sufficiently well from thermodynamic data on the short polyphenyl isomers and g. l. c. data on benzene dissolved in them so that the application of the models with minimal empirical adjustment can be justified. Fit with experimental data is entirely satisfactory. Simpler models ordinarily used, which include only Flory-Huggins entropy of mixing and regular solution or rigid lattice approximations for the heat of mixing, may thus neglect contributions similar in magnitude to those included. The practical significance of the various contribution...

A decorated lattice model for two‐ and three‐component liquid systems proposed by Widom and extended by Clark and Neece is used to discuss the phase behavior of ternary systems. The binodal curves with their associated plait points are investigated for several systems lying within the framework of the model. Some results on the degree of the binodal curve, the heat capacity, and the composition fluctuations in the vicinity of the plait point, as found by Widom and Clark, are shown to hold in general for all systems discussed.

Because of the loss of ductility with exposure to oxidizing conditions, long time applications of titanium alloys have been limited to temperatures below 700 K and short time applications have been limited to temperatures below 815 K. Oxygen barrier coatings for shielding Ti-6Al-2Sn-4Zr-2Mo alloy from oxidation during exposure to high temperatures were studied using foil gage specimens. The coatings included micrometer-thick sputtered SiO2 and chemical-vapor-deposited silicate layers both with and without an aluminum basecoat. The oxidation rates and resistance to embrittlement of the coated specimens were significantly better than those of the uncoated specimens.

The effects of simulated reentry heating on the emittance of TD-NiCr were investigated, Groups of specimens were subjected to three different preconditioning treatments, Specimens from each group were exposed to 6, 24, and 30 half-hour simulated reentry exposure cycles in a supersonic arc tunnel at each of three conditions intended to produce surface temperatures of 1255, 1365, and 1475 K. Spectral and total normal emittance were determined at 1300 K on specimens which had been preconditioned only and specimens after completion of reentry simulation exposure. Oxide morphology and chemistry were studied by scanning electron microscopy and X-ray diffraction analysis.